Wasmtime: Miscompiled guest heap access enables sandbox escape on aarch64 Cranelift

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-34971: 0.32% estimated exploitation activity in the next 30 days; percentile 24.88 (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 Cranelift compilation backend contains a bug on aarch64 when performing a certain shape of heap accesses which means that the wrong address is accessed. When combined with explicit bounds checks a guest WebAssembly module this can create a situation where there are two diverging computations for the same address: one for the address to bounds-check and one for the address to load. This difference in address being operated on means that a guest module can pass a bounds check but then load a different address. Combined together this enables an arbitrary read/write primitive for guest WebAssembly when accesssing host memory. This is a sandbox escape as guests are able to read/write arbitrary host memory. This vulnerability has a few ingredients, all of which must be met, for this situation to occur and bypass the sandbox restrictions: This miscompiled shape of load only occurs on 64-bit WebAssembly linear memories, or when Config::wasmmemory64 is enabled. 32-bit…

Published by the source

9 Apr 2026, 20:23 UTC

Last modified by the source

15 Apr 2026, 20:55 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-jhxm-h53p-jm7w

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# Patch Next advisory brief: CVE-2026-34971

Advisory: Wasmtime: Miscompiled guest heap access enables sandbox escape on aarch64 Cranelift
IDs: CVE-2026-34971, GHSA-jhxm-h53p-jm7w
Record: https://patchnext.com/advisories/cve-2026-34971 (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: Critical (CVSS 9.0)
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 >= 32.0.0, < 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-jhxm-h53p-jm7w (GitHub-reviewed advisory GHSA-jhxm-h53p-jm7w lists affected ranges: crates.io wasmtime >=32.0.0 =37.0.0 =43.0.0 <=43.0.0)

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