Wasmtime is vulnerable to panic when dropping a [Typed]Func::call_async future

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · 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 · score source

EPSS

• CVE-2026-27195: 0.41% estimated exploitation activity in the next 30 days; percentile 35.50 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

The affected versions of Wasmtime can panic if the host embedder drops the future returned by wasmtime::component::[Typed]Func::callasync before it resolves. Details Starting with Wasmtime 39.0.0, the component-model-async feature became the default, which brought with it a new implementation of [Typed]Func::callasync which made it capable of calling async-typed guest export functions. However, that implementation had a bug leading to a panic under certain circumstances: 1. The host embedding calls [Typed]Func::callasync on a function exported by a component, polling the returned Future once. 2. The component function yields control to the async runtime (e.g. Tokio), e.g. due to a call to host function registered using LinkerInstance::funcwrapasync which yields, or due an epoch interruption. 3. 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. 4. The host embedding…

Published by the source

24 Feb 2026, 20:44 UTC

Last modified by the source

27 Feb 2026, 20:24 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-xjhv-v822-pf94

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# Patch Next advisory brief: CVE-2026-27195

Advisory: Wasmtime is vulnerable to panic when dropping a `[Typed]Func::call_async` future
IDs: CVE-2026-27195, GHSA-xjhv-v822-pf94
Record: https://patchnext.com/advisories/cve-2026-27195 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: wasmtime 41.0.4, 40.0.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime: affected >= 39.0.0, < 40.0.4; >= 41.0.0, < 41.0.4; fixed in 41.0.4, 40.0.4

## Suggested inspection (read-only)
- crates.io wasmtime: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on wasmtime.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-xjhv-v822-pf94 (GitHub-reviewed advisory GHSA-xjhv-v822-pf94 lists affected ranges: crates.io wasmtime >=39.0.0 =41.0.0 <41.0.4)

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