Wasmtime can panic when adding excessive fields to a wasi:http/types.fields instance

Exploitation

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

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H · score source

EPSS

• CVE-2026-27572: 0.52% estimated exploitation activity in the next 30 days; percentile 44.13 (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.

Impact Wasmtime's implementation of the wasi:http/types.fields resource is susceptible to panics when too many fields are added to the set of headers. Wasmtime's implementation in the wasmtime-wasi-http crate is backed by a data structure which panics when it reaches excessive capacity and this condition was not handled gracefully in Wasmtime. Panicking in a WASI implementation is a Denial of Service vector for embedders and is treated as a security vulnerability in Wasmtime. Patches Wasmtime 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 patch this vulnerability and return a trap to the guest instead of panicking. Workarounds There are no known workarounds at this time, embedders are encouraged to update to a patched version of Wasmtime. Resources Limitations of http::HeaderMap

Published by the source

24 Feb 2026, 21:08 UTC

Last modified by the source

27 Feb 2026, 20:25 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-243v-98vx-264h

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# Patch Next advisory brief: CVE-2026-27572

Advisory: Wasmtime can panic when adding excessive fields to a `wasi:http/types.fields` instance
IDs: CVE-2026-27572, GHSA-243v-98vx-264h
Record: https://patchnext.com/advisories/cve-2026-27572 (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 40.0.4, 36.0.6, 24.0.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime: affected < 24.0.6; >= 25.0.0, < 36.0.6; >= 37.0.0, < 40.0.4; fixed in 24.0.6, 40.0.4, 36.0.6

## 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-243v-98vx-264h (GitHub-reviewed advisory GHSA-243v-98vx-264h lists affected ranges: crates.io wasmtime >=0 =25.0.0 =37.0.0 <40.0.4)

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