Wasmtime has host panic when Winch compiler executes table.fill

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-34946: 0.36% estimated exploitation activity in the next 30 days; percentile 29.58 (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 Winch compiler contains a vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring, #11254, changed how compiled code referenced tables within the table. instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. Patches Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are…

Published by the source

9 Apr 2026, 20:23 UTC

Last modified by the source

24 Apr 2026, 21:03 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-q49f-xg75-m9xw

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# Patch Next advisory brief: CVE-2026-34946

Advisory: Wasmtime has host panic when Winch compiler executes `table.fill`
IDs: CVE-2026-34946, GHSA-q49f-xg75-m9xw
Record: https://patchnext.com/advisories/cve-2026-34946 (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 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: wasmtime 43.0.1, 42.0.2, 36.0.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime: affected >= 25.0.0, < 36.0.7; >= 37.0.0, < 42.0.2; >= 43.0.0, <= 43.0.0; fixed in 36.0.7, 43.0.1, 42.0.2

## 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-q49f-xg75-m9xw (GitHub-reviewed advisory GHSA-q49f-xg75-m9xw lists affected ranges: crates.io wasmtime >=25.0.0 =37.0.0 =43.0.0 <=43.0.0)

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