wasmtime

Version	Released
`48.0.2` patch	Sep 10, 2026
`36.0.15` patch	Sep 10, 2026
`49.0.0-rc.1` pre	Sep 05, 2026
`48.0.1` patch	Aug 24, 2026
`36.0.14` patch	Aug 20, 2026
`46.0.3` patch	Aug 20, 2026
`47.0.4` patch	Aug 20, 2026
`24.0.13` patch	Aug 20, 2026
`48.0.0` major	Aug 20, 2026
`47.0.3` patch 2 CVEs	Jul 31, 2026
`46.0.2` patch 2 CVEs	Jul 31, 2026
`36.0.13` patch 1 CVE	Jul 31, 2026
`24.0.12` patch 1 CVE	Jul 31, 2026
`47.0.2` patch 4 CVEs	Jul 21, 2026
`47.0.1` patch 4 CVEs	Jul 20, 2026
`47.0.0` major 4 CVEs	Jul 20, 2026
`36.0.12` patch 2 CVEs	Jun 24, 2026
`45.0.3` patch 2 CVEs	Jun 24, 2026
`46.0.1` patch 4 CVEs	Jun 24, 2026
`24.0.11` patch 2 CVEs	Jun 24, 2026
`46.0.0` major 4 CVEs	Jun 22, 2026
`24.0.10` patch 2 CVEs	Jun 15, 2026
`44.0.3` patch 2 CVEs	Jun 15, 2026
`45.0.2` patch 2 CVEs	Jun 15, 2026
`36.0.11` patch 2 CVEs	Jun 15, 2026
`45.0.1` patch 2 CVEs	Jun 05, 2026
`44.0.2` patch 2 CVEs	May 21, 2026
`36.0.10` patch 2 CVEs	May 21, 2026
`45.0.0` major 2 CVEs	May 21, 2026
`24.0.9` patch 2 CVEs	May 21, 2026
`36.0.9` patch 2 CVEs	May 05, 2026
`36.0.8` patch 2 CVEs	Apr 30, 2026
`43.0.2` patch 2 CVEs	Apr 30, 2026
`44.0.1` patch 2 CVEs	Apr 30, 2026
`24.0.8` patch 2 CVEs	Apr 30, 2026
`44.0.0` major 2 CVEs	Apr 20, 2026
`42.0.2` patch 3 CVEs	Apr 09, 2026
`43.0.1` patch 3 CVEs	Apr 09, 2026
`36.0.7` patch 3 CVEs	Apr 09, 2026
`24.0.7` patch 2 CVEs	Apr 09, 2026
`43.0.0` major 15 CVEs	Mar 20, 2026
`42.0.1` patch 14 CVEs	Feb 25, 2026
`41.0.4` patch 14 CVEs	Feb 24, 2026
`40.0.4` patch 14 CVEs	Feb 24, 2026
`42.0.0` major 14 CVEs	Feb 24, 2026
`24.0.6` patch 7 CVEs	Feb 24, 2026
`36.0.6` patch 14 CVEs	Feb 24, 2026
`41.0.3` patch 15 CVEs	Feb 04, 2026
`41.0.2` patch 15 CVEs	Feb 03, 2026
`40.0.3` patch 17 CVEs	Jan 27, 2026

48.0.2 patch

Sep 10, 2026

36.0.15 patch

Sep 10, 2026

49.0.0-rc.1 pre

Sep 05, 2026

48.0.1 patch

Aug 24, 2026

36.0.14 patch

Aug 20, 2026

46.0.3 patch

Aug 20, 2026

47.0.4 patch

Aug 20, 2026

24.0.13 patch

Aug 20, 2026

48.0.0 major

Aug 20, 2026

47.0.3 patch

2 CVEs

Jul 31, 2026

46.0.2 patch

2 CVEs

Jul 31, 2026

36.0.13 patch

1 CVE

Jul 31, 2026

24.0.12 patch

1 CVE

Jul 31, 2026

47.0.2 patch

4 CVEs

Jul 21, 2026

47.0.1 patch

4 CVEs

Jul 20, 2026

47.0.0 major

4 CVEs

Jul 20, 2026

36.0.12 patch

2 CVEs

Jun 24, 2026

45.0.3 patch

2 CVEs

Jun 24, 2026

46.0.1 patch

4 CVEs

Jun 24, 2026

24.0.11 patch

2 CVEs

Jun 24, 2026

46.0.0 major

4 CVEs

Jun 22, 2026

24.0.10 patch

2 CVEs

Jun 15, 2026

44.0.3 patch

2 CVEs

Jun 15, 2026

45.0.2 patch

2 CVEs

Jun 15, 2026

36.0.11 patch

2 CVEs

Jun 15, 2026

45.0.1 patch

2 CVEs

Jun 05, 2026

44.0.2 patch

2 CVEs

May 21, 2026

36.0.10 patch

2 CVEs

May 21, 2026

45.0.0 major

2 CVEs

May 21, 2026

24.0.9 patch

2 CVEs

May 21, 2026

36.0.9 patch

2 CVEs

May 05, 2026

36.0.8 patch

2 CVEs

Apr 30, 2026

43.0.2 patch

2 CVEs

Apr 30, 2026

44.0.1 patch

2 CVEs

Apr 30, 2026

24.0.8 patch

2 CVEs

Apr 30, 2026

44.0.0 major

2 CVEs

Apr 20, 2026

42.0.2 patch

3 CVEs

Apr 09, 2026

43.0.1 patch

3 CVEs

Apr 09, 2026

36.0.7 patch

3 CVEs

Apr 09, 2026

24.0.7 patch

2 CVEs

Apr 09, 2026

43.0.0 major

15 CVEs

RUSTSEC-2026-0269 GHSA-vqjp-4c8c-hfgg Aug 20, 2026

Filesystem sandbox escape when paths or symlinks contain trailing slashes

Critical

Network Low Low

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-vqjp-4c8c-hfgg For more information see the GitHub-hosted security advisory.

Fixed in


          24.0.13


          36.0.14


          46.0.3


          47.0.4

References

Updated Aug 31, 2026 · Source: OSV.dev

RUSTSEC-2026-0222 GHSA-hgjw-h833-99q9 Jul 31, 2026

Stores can mix up type indices between engines

3.8 / 10

Low

Local High High Required Unchanged Low Low Low

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hgjw-h833-99q9 For more information see the GitHub-hosted security advisory.

Fixed in


          24.0.12


          36.0.13


          46.0.2


          47.0.3

References

Updated Jul 31, 2026 · Source: OSV.dev

CVE-2026-44216 GHSA-p8xm-42r7-89xg RUSTSEC-2026-0114 May 07, 2026

wasmtime has a panic when allocating a table exceeding the size of the host's address space

Medium

Network Low Low

Impact

Wasmtime's allocation logic for a WebAssembly table contained checked arithmetic which panicked on overflow. This overflow is possible to trigger, and thus panic, when a table with an extremely large size is allocated. This is possible with the WebAssembly memory64 proposal where tables can have sizes in the 64-bit range as opposed to the previous 32-bit range which would not overflow. The panic happens when attempting to create a very large table, such as when instantiating a WebAssembly module or component.

This bug does not affect the pooling allocator which limits tables sizes to much less than the required amount to trigger the overflow. This bug is only present for the on-demand instance allocator, which is Wasmtime's default allocator. This bug also requires the memory64 WebAssembly feature to be enabled, which is on-by-default.

Panicking in the host process is considered a denial-of-service vector for Wasmtime.

Patches

Wasmtime 36.0.8, 43.0.2, and 44.0.1 have all been released which fixes this issue.

Workarounds

Embeddings can switch to using the pooling allocator to work around this issue, or the memory64 WebAssembly proposal can be disabled. Otherwise there is no workaround and users are recommended to upgrade.

Fixed in


          36.0.8


          43.0.2

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-35186 GHSA-f984-pcp8-v2p7 RUSTSEC-2026-0094 Apr 10, 2026

Wasmtime has improperly masked return value from `table.grow` with Winch compiler backend

Medium

Network High Low None

Impact

Wasmtime's Winch compiler backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally in Winch, is tagged as a 64-bit value instead of a 32-bit value. This invalid internal representation of Winch's compiler state compounds into further issues depending on how the value is consumed.

One example can be seen when the result of table.grow is used as the address of a load operation. The load operation is tricked into thinking the address is a 64-bit value, not a 32-bit value, which means that the final address to load from is calculated incorrectly. This can lead to a situation where the bytes before the start of linear memory can be loaded/stored to.

The primary consequence of this bug is that bytes in the host's address space can be stored/read from. This is only applicable to the 16 bytes before linear memory, however, as the only significant return value of table.grow that can be misinterpreted is -1. The bytes before linear memory are, by default, unmapped memory. Wasmtime will detect this fault and abort the process, however, because wasm should not be able to access these bytes.

Overall this this bug in Winch represents a DoS vector by crashing the host process, a correctness issue within Winch, and a possible leak of up to 16-bytes before linear memory. Wasmtime's default compiler is Cranelift, not Winch, and Wasmtime's default settings are to place guard pages before linear memory. This means that Wasmtime's default configuration is not affected by this issue, and when explicitly choosing Winch Wasmtime's otherwise default configuration leads to a DoS. Disabling guard pages before linear memory is required to possibly leak up to 16-bytes of host data.

Patches

Wasmtime 43.0.1, 42.0.2, and 36.0.7 have been released with fixes for this issue.

Workaround

There are no workarounds within the Winch compiler backend while using the affected versions. Users of Wasmtime are encouraged either to upgrade to patched versions or, if that is not possible, use the Cranelift compiler backend.

Affected versions


          43.0.0

Fixed in


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34987 GHSA-xx5w-cvp6-jv83 RUSTSEC-2026-0095 Apr 10, 2026

Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access

Critical

Network Low None None

Impact

Wasmtime with its Winch (baseline) non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox.

This vulnerability requires use of the Winch compiler (-Ccompiler=winch). By default, Wasmtime uses its Cranelift backend, not Winch. With Winch, the same incorrect assumption is present in theory on both aarch64 and x86-64. The aarch64 case has an observed-working proof of concept, while the x86-64 case is theoretical and may not be reachable in practice.

This Winch compiler bug can allow the Wasm guest to access memory before or after the linear-memory region, independently of whether pre- or post-guard regions are configured. The accessible range in the initial bug proof-of-concept is up to 32KiB before the start of memory, or ~4GiB after the start of memory, independently of the size of pre- or post-guard regions or the use of explicit or guard-region-based bounds checking. However, the underlying bug assumes a 32-bit memory offset stored in a 64-bit register has its upper bits cleared when it may not, and so closely related variants of the initial proof-of-concept may be able to access truly arbitrary memory in-process. This could result in a host process segmentation fault (DoS), an arbitrary data leak from the host process, or with a write, potentially an arbitrary RCE.

Patches

Wasmtime 43.0.1, 42.0.2, and 36.0.7 have been released with fixes for this issue.

Workaround

There are no workarounds within the Winch compiler backend while using the affected versions. Users of Wasmtime are encouraged either to upgrade to patched versions or, if that is not possible, use the Cranelift compiler backend.

Affected versions


          43.0.0

Fixed in


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-35195 GHSA-394w-hwhg-8vgm RUSTSEC-2026-0091 Apr 09, 2026

Wasmtime has out-of-bounds write or crash when transcoding component model strings

Medium

Network Low Low None

Impact

Wasmtime's implementation of transcoding strings between components contains a bug where the return value of a guest component's realloc is not validated before the host attempts to write through the pointer. This enables a guest to cause the host to write arbitrary transcoded string bytes to an arbitrary location up to 4GiB away from the base of linear memory. These writes on the host could hit unmapped memory or could corrupt host data structures depending on Wasmtime's configuration.

Wasmtime by default reserves 4GiB of virtual memory for a guest's linear memory meaning that this bug will by default on hosts cause the host to hit unmapped memory and abort the process due to an unhandled fault. Wasmtime can be configured, however, to reserve less memory for a guest and to remove all guard pages, so some configurations of Wasmtime may lead to corruption of data outside of a guest's linear memory, such as host data structures or other guests's linear memories.

Patches

Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

There is no known workaround for this issue and affected hosts/embeddings are recommended to upgrade.

Affected versions


          43.0.0

Fixed in


          24.0.7


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34988 GHSA-6wgr-89rj-399p RUSTSEC-2026-0088 Apr 09, 2026

Wasmtime has data leakage between pooling allocator instances

Low

Network High Low None

Impact

Wasmtime's implementation of its pooling allocator contains a bug where in certain configurations the contents of linear memory can be leaked from one instance to the next. The implementation of resetting the virtual memory permissions for linear memory used the wrong predicate to determine if resetting was necessary, where the compilation process used a different predicate. This divergence meant that the pooling allocator incorrectly deduced at runtime that resetting virtual memory permissions was not necessary while compile-time determine that virtual memory could be relied upon.

Exposing this bug requires specific configuration values to be used. If any of these configurations are not applicable then this bug does not happen:

The pooling allocator must be in use.
The Config::memory_guard_size configuration option must be 0.
The Config::memory_reservation configuration must be less than 4GiB.
The pooling allocator must be configured with max_memory_size the same as the memory_reservation value.

If all of these conditions are applicable then when a linear memory is reused the VM permissions of the previous iteration are not reset. This means that the compiled code, which is assuming out-of-bounds loads will segfault, will not actually segfault and can read the previous contents of linear memory if it was previously mapped.

This represents a data leakage vulnerability between guest WebAssembly instances which breaks WebAssembly's semantics and additionally breaks the sandbox that Wasmtime provides. Wasmtime is not vulnerable to this issue with its default settings, nor with the default settings of the pooling allocator, but embeddings are still allowed to configure these values to cause this vulnerability.

Patches

Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

All four conditions above must be met to be vulnerable to this bug, and users can work around this bug by adjusting any of the above conditions. For example it is strongly recommended that guard pages are configured for linear memories which would make this bug not applicable.

Affected versions


          43.0.0

Fixed in


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34983 GHSA-hfr4-7c6c-48w2 PYSEC-2026-151 RUSTSEC-2026-0090 Apr 09, 2026

Wasmtime has use-after-free bug after cloning `wasmtime::Linker`

Low

Physical High High

Impact

In version 43.0.0 of the wasmtime crate, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs.

This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host.

The typical symptom of this use-after-free bug is a segfault. It does not enable heap corruption or data leakage.

If you are using the wasmtime CLI, rather than the embedding API, you are not affected. If you are using the embedding API but are not calling wasmtime::Linker's Clone implementation, you are not affected.

Specifically, the following steps must occur to trigger the bug:

Clone a wasmtime::Linker
Drop the original linker instance
Use the new, cloned linker instance, resulting in a use-after-free

Patches

This bug has been patched in Wasmtime version 43.0.1

Workarounds

Wasmtime embedders are highly encouraged to upgrade their wasmtime crate dependency.

If upgrading is not an option, or as a temporary workaround before upgrading, you can avoid this bug by not cloning wasmtime::Linker and instead creating a new, empty wasmtime::Linker and manually reregistering the host APIs from the original linker:

use wasmtime::{Linker, Result, Store};

fn clone_linker<T>(linker: &Linker<T>, store: &mut Store<T>) -> Result<Linker<T>> {
    let mut cloned = Linker::new();
    for (module, name, item) in linker.iter(store) {
        cloned.define(module, name, item)?;
    }
    Ok(cloned)
}

References

This bug was introduced during an internal refactoring that was part of our efforts to robustly handle allocation failure in Wasmtime. This refactoring introduced an string-interning pool which had an unsound TryClone[^try-clone] implementation.

[^try-clone]: The TryClone trait is our version of the Rust standard library's Clone trait that allows for returning OutOfMemory errors.

The StringPool was introduced in https://github.com/bytecodealliance/wasmtime/pull/12536, at which time the bug in TryClone for StringPool was already present, although this code path was not yet used anywhere.
wasmtime::Linker was refactored to internally use StringPool in https://github.com/bytecodealliance/wasmtime/pull/12537, at which time the buggy code path became accessible.
This bug was originally reported to the Wasmtime maintainers as https://github.com/bytecodealliance/wasmtime/pull/12906

Affected versions


          43.0.0

Fixed in


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34971 GHSA-jhxm-h53p-jm7w RUSTSEC-2026-0096 Apr 09, 2026

Wasmtime: Miscompiled guest heap access enables sandbox escape on aarch64 Cranelift

Critical

Network Low Low None

Impact

Wasmtime's Cranelift compilation backend contains a bug on aarch64 when performing a certain shape of heap accesses which means that the wrong address is accessed. When combined with explicit bounds checks a guest WebAssembly module this can create a situation where there are two diverging computations for the same address: one for the address to bounds-check and one for the address to load. This difference in address being operated on means that a guest module can pass a bounds check but then load a different address. Combined together this enables an arbitrary read/write primitive for guest WebAssembly when accesssing host memory. This is a sandbox escape as guests are able to read/write arbitrary host memory.

This vulnerability has a few ingredients, all of which must be met, for this situation to occur and bypass the sandbox restrictions:

This miscompiled shape of load only occurs on 64-bit WebAssembly linear memories, or when Config::wasm_memory64 is enabled. 32-bit WebAssembly is not affected.
Spectre mitigations or signals-based-traps must be disabled. When spectre mitigations are enabled then the offending shape of load is not generated. When signals-based-traps are disabled then spectre mitigations are also automatically disabled.

The specific bug in Cranelift is a miscompile of a load of the shape load(iadd(base, ishl(index, amt))) where amt is a constant. The amt value is masked incorrectly to test if it's a certain value, and this incorrect mask means that Cranelift can pattern-match this lowering rule during instruction selection erroneously, diverging from WebAssembly's and Cranelift's semantics. This incorrect lowering would, for example, load an address much further away than intended as the correct address's computation would have wrapped around to a smaller value insetad.

Patches

Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

This bug only affects users of Cranelift on aarch64. Cranelift on other platforms is not affected. Additionally this only affects 64-bit WebAssembly linear memories, so if Config::wasm_memory64 is disabled then hosts are not affected. Note that Config::wasm_memory64 is enabled by default. If spectre mitigations are enabled, which are enabled by default, then hosts are not affected by this issue.

Affected versions


          43.0.0

Fixed in


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34946 GHSA-q49f-xg75-m9xw RUSTSEC-2026-0089 Apr 09, 2026

Wasmtime has host panic when Winch compiler executes `table.fill`

Medium

Network Low Low

Impact

Wasmtime's Winch compiler contains a vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic.

The specific issue is that a historical refactoring, #11254, changed how compiled code referenced tables within the table.* instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table.

Patches

Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

Users of Cranelift are not affected by this issue, but for users of Winch there is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

Affected versions


          43.0.0

Fixed in


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34945 GHSA-m9w2-8782-2946 RUSTSEC-2026-0086 Apr 09, 2026

Wasmtime has host data leakage with 64-bit tables and Winch

Low

Network Low Low None

Impact

Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests.

This bug specifically arose from a mistake where the return value of table.size was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime.

Patches

Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

Users of Cranelift are not affected by this issue, but users of Winch have no workarounds other than disabling the Config::wasm_memory64 proposal.

Affected versions


          43.0.0

Fixed in


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34944 GHSA-qqfj-4vcm-26hv RUSTSEC-2026-0087 Apr 09, 2026

Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64

Medium

Local Low Low

On x86-64 platforms with SSE3 disabled Wasmtime's compilation of the f64x2.splat WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages disabled it's possible for out-of-sandbox data to be loaded, but this data is not visible to WebAssembly guests.

Details

The f64x2.splat operator, when operating on a value loaded from a memory (for example with f64.load), compiles with Cranelift to code on x86-64 without SSE3 that loads 128 bits (16 bytes) rather than the expected 64 bits (8 bytes) from memory. When the address is in-bounds for a (correct) 8-byte load but not an (incorrect) 16-byte load, this can load beyond memory by up to 8 bytes. This can result in three different behaviors depending on Wasmtime's configuration:

If guard pages are disabled then this extra data will be loaded. The extra data is present in the upper bits of a register, but the upper bits are not visible to WebAssembly guests. Actually witnessing this data would require a different bug in Cranelift, of which none are known. Thus in this situation while it's something we're patching in Cranelift it's not a security issue.
If guard pages are enabled, and signals-based-traps are enabled, then this operation will result in a safe WebAssembly trap. The trap is incorrect because the load is not out-of-bounds as defined by WebAssembly, but this mistakenly widened load will load bytes from an unmapped guard page, causing a segfault which is caught and handled as a Wasm trap. In this situation this is not a security issue, but we're patching Cranelift to fix the WebAssembly behavior.
If guard pages are enabled, and signals-based-traps are disabled, then this operation results in an uncaught segfault. Like the previous case with guard pages enabled this will load from an unmapped guard page. Unlike before, however, signals-based-traps are disabled meaning that signal handlers aren't configured. The resulting segfault will, by default, terminate the process. This is a security issue from a DoS perspective, but does not represent an arbitrary read or write from WebAssembly, for example.

Wasmtime's default configuration is case (2) in this case. That means that Wasmtime, by default, incorrectly executes this WebAssembly instruction but does not have insecure behavior.

Impact

If signals-based-traps are disabled and guard pages are enabled then guests can trigger an uncaught segfault in the host, likely aborting the host process. This represents, for example, a DoS vector for WebAssembly guests.

This bug does not affect Wasmtime's default configuration and requires signals-based-traps to be disabled. This bug only affects the x86-64 target with the SSE3 feature disabled and the Cranelift backend (Wasmtime's default backend).

Patches

Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

This bug only affects x86-64 hosts where SSE3 is disabled. If SSE3 is enabled or if a non-x86-64 host is used then hosts are not affect. Otherwise there are no known workarounds to this issue.

Affected versions


          43.0.0

Fixed in


          24.0.7


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34943 GHSA-m758-wjhj-p3jq RUSTSEC-2026-0085 Apr 09, 2026

Wasmtime has a possible panic when lifting `flags` component value

Medium

Network High High

Impact

Wasmtime contains a possible panic which can happen when a flags-typed component model value is lifted with the Val type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into Val, not when using the flags! macro. This additionally only affects flags-typed values which are part of a WIT interface.

This has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector.

Patches

Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

There is no workaround for this bug if a host meets the criteria to be affected. To be affected a host must be using wasmtime::component::Val and possibly work with a flags type in the component model.

Affected versions


          43.0.0

Fixed in


          24.0.7


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34942 GHSA-jxhv-7h78-9775 RUSTSEC-2026-0092 Apr 09, 2026

Wasmtime: Panic when transcoding misaligned utf-16 strings

Medium

Network Low Low

Impact

Wasmtime's implementation of transcoding strings into the Component Model's utf16 or latin1+utf16 encodings improperly verified the alignment of reallocated strings. This meant that unaligned pointers could be passed to the host for transcoding which would trigger a host panic. This panic is possible to trigger from malicious guests which transfer very specific strings across components with specific addresses.

Host panics are considered a DoS vector in Wasmtime as the panic conditions are controlled by the guest in this situation.

Patches

Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

There is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

Affected versions


          43.0.0

Fixed in


          24.0.7


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

CVE-2026-34941 GHSA-hx6p-xpx3-jvvv RUSTSEC-2026-0093 Apr 09, 2026

Wasmtime: Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding

Medium

Network Low Low

Summary

Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units.

This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16.

A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled.

Impact

This is an out-of-bounds memory access. Any user running untrusted wasm components that use cross-component string passing (with UTF-16 source and latin1+utf16 destination encodings) is affected.

With guard pages: Denial of service. The host process crashes with SIGBUS/SIGSEGV.
Without guard pages: Potential information disclosure. The guest can read host memory beyond its linear memory allocation.

Patches

Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime. Workarounds

There is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

Affected versions


          43.0.0

Fixed in


          24.0.7


          36.0.7


          42.0.2


          43.0.1

References

Updated Sep 10, 2026 · Source: OSV.dev

Mar 20, 2026

42.0.1 patch

14 CVEs

Feb 25, 2026

41.0.4 patch

14 CVEs

Feb 24, 2026

40.0.4 patch

14 CVEs

Feb 24, 2026

42.0.0 major

14 CVEs

Feb 24, 2026

24.0.6 patch

7 CVEs

Feb 24, 2026

36.0.6 patch

14 CVEs

Feb 24, 2026

41.0.3 patch

15 CVEs

Feb 04, 2026

41.0.2 patch

15 CVEs

Feb 03, 2026

40.0.3 patch

17 CVEs

Jan 27, 2026

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