bytecodealliance wasmtime up to 40.0.3/41.0.3 exceptional condition

Summaryinfo

A vulnerability was found in bytecodealliance wasmtime up to 40.0.3/41.0.3. It has been classified as problematic. Affected by this issue is some unknown functionality. Performing a manipulation results in exceptional condition. This vulnerability is reported as CVE-2026-27195. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in bytecodealliance wasmtime up to 40.0.3/41.0.3. It has been classified as problematic. This affects an unknown code block. The manipulation with an unknown input leads to a exceptional condition vulnerability. CWE is classifying the issue as CWE-755. The product does not handle or incorrectly handles an exceptional condition. This is going to have an impact on availability. The summary by CVE is:

Wasmtime is a runtime for WebAssembly. Starting with Wasmtime 39.0.0, the `component-model-async` feature became the default, which brought with it a new implementation of `[Typed]Func::call_async` which made it capable of calling async-typed guest export functions. However, that implementation had a bug leading to a panic under certain circumstances: First, the host embedding calls `[Typed]Func::call_async` on a function exported by a component, polling the returned `Future` once. Second, the component function yields control to the async runtime (e.g. Tokio), e.g. due to a call to host function registered using `LinkerInstance::func_wrap_async` which yields, or due an epoch interruption. Third, the host embedding drops the `Future` after polling it once. This leaves the component instance in a non-reenterable state since the call never had a chance to complete. Fourth, the host embedding calls `[Typed]Func::call_async` again, polling the returned `Future`. Since the component instance cannot be entered at this point, the call traps, but not before allocating a task and thread for the call. Fifth, the host embedding ignores the trap and drops the `Future`. This panics due to the runtime attempting to dispose of the task created above, which panics since the thread has not yet exited. When a host embedder using the affected versions of Wasmtime calls `wasmtime::component::[Typed]Func::call_async` on a guest export and then drops the returned future without waiting for it to resolve, and then does so again with the same component instance, Wasmtime will panic. Embeddings that have the `component-model-async` compile-time feature disabled are unaffected. Wasmtime 40.0.4 and 41.0.4 have been patched to fix this issue. Versions 42.0.0 and later are not affected. If an embedding is not actually using any component-model-async features then disabling the `component-model-async` Cargo feature can work around this issue. This issue can also be worked around by either ensuring every `call_async` future is awaited until it completes or refraining from using the `Store` again after dropping a not-yet-resolved `call_async` future.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-27195 since 02/18/2026. The exploitability is told to be difficult. It is possible to initiate the attack remotely. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 40.0.4 or 41.0.4 eliminates this vulnerability.

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Productinfo

Vendor

• bytecodealliance

Name

• wasmtime

Version

• 40.0.0
• 40.0.1
• 40.0.2
• 40.0.3
• 41.0.0
• 41.0.1
• 41.0.2
• 41.0.3

Website

• Product: https://github.com/bytecodealliance/wasmtime/

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