Skip to content
Patch Next
Sign inAdd to your agent

← Actionable
Critical, CVSS 9.9amended

Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation

CVE-2026-115889GHSA-897f-g5gm-fmxm

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (wasmtime 43.0.0, 36.0.19), 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.

Add to your agent

Affected packages

  • crates.io wasmtime

    Affected
    < 36.0.19>= 37.0.0, < 43.0.0
    Fixed in
    43.0.0, 36.0.19

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.9 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
EPSS
  • CVE-2026-115889: 0.45% estimated exploitation activity in the next 30 days; percentile 39.45 (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.

Summary In Wasmtime prior to v43, the Cranelift compiler backend bit-packs its SSA value indices in a way that can result in silent overflow in release builds, and result in incorrect value references in the IR resulting in arbitrary miscompilation. A very large Wasm function body, or one that is specially crafted to use many SSA values, can use this to force type-confusion or other arbitrary side-effects and escape the sandbox. Cranelift was changed in Wasmtime v43 to use a full u32 index, with checks if that limit is exceeded, and so is no longer susceptible to this bug. Impact A Wasmtime engine with default settings (using the Cranelift backend) on any architecture/platform could experience a sandbox escape from a specially-crafted Wasm module. Patches Wasmtime v36.0.19 has been released which fixes this issue.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-897f-g5gm-fmxm

  2. Revision 3 · amended ·

    Amended from ghsa record GHSA-897f-g5gm-fmxm

  3. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  4. Revision 1 · created ·

    Published from osv record RUSTSEC-2026-0380

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-2026-115889

Advisory: Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
IDs: CVE-2026-115889, GHSA-897f-g5gm-fmxm
Record: https://patchnext.com/advisories/rustsec-2026-0380 (revision 4, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: wasmtime 43.0.0, 36.0.19. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime: affected < 36.0.19; >= 37.0.0, < 43.0.0; fixed in 43.0.0, 36.0.19

## 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://osv.dev/vulnerability/RUSTSEC-2026-0380 (OSV record RUSTSEC-2026-0380 lists affected ranges: crates.io wasmtime >=0.0.0-0 =37.0.0 <43.0.0 (fixed))
- Verified: https://github.com/advisories/GHSA-897f-g5gm-fmxm (GitHub-reviewed advisory GHSA-897f-g5gm-fmxm lists affected ranges: crates.io wasmtime >=0 =37.0.0 <43.0.0)

Commands are suggestions: review each one before running it.

Loading voting…