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Low, CVSS 2.3

Wasmtime has host data leakage with 64-bit tables and Winch

CVE-2026-34945GHSA-m9w2-8782-2946

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (wasmtime 43.0.1, 42.0.2, 36.0.7), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • 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

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
2.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N · score source
EPSS
  • CVE-2026-34945: 0.32% estimated exploitation activity in the next 30 days; percentile 25.48 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests. This bug specifically arose from a mistake where the return value of table.size was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime. Patches Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-m9w2-8782-2946

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-34945

Advisory: Wasmtime has host data leakage with 64-bit tables and Winch
IDs: CVE-2026-34945, GHSA-m9w2-8782-2946
Record: https://patchnext.com/advisories/cve-2026-34945 (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: Low (CVSS 2.3)
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-m9w2-8782-2946 (GitHub-reviewed advisory GHSA-m9w2-8782-2946 lists affected ranges: crates.io wasmtime >=25.0.0 =37.0.0 =43.0.0 <=43.0.0)

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