CVE-2026-27195 Wasmtime is vulnerable to panic when dropping a `[Typed]Func::call_async` future

What is CVE-2026-27195?

CVE-2026-27195 is a medium-severity denial of service vulnerability in bytecodealliance wasmtime, published on 24 Feb 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official description

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.

Weakness: CWE-755

Which versions are affected by CVE-2026-27195?

5 open source packages ship an affected version, including wasmtime. It affects 1 product.

Products include Bytecodealliance Wasmtime.

How do I fix CVE-2026-27195?

Upgrade wasmtime to a fixed version for your release line: 40.0.4 or 41.0.4.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-27195 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27195 exists.

Other vulnerabilities in bytecodealliance wasmtime

• CVE-2026-34971 Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift Critical 9.0
• CVE-2026-34987 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access Critical 9.0
• CVE-2022-39393 Wasmtime vulnerable to data leakage between instances in the pooling allocator High 8.6
• CVE-2022-24791 Use after free in Wasmtime High 8.1
• CVE-2026-47261 Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction High 7.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-xjhv-v822-pf94, JLSEC-2026-1351, RUSTSEC-2026-0022.