---
id: CVE-2026-115889
title: >-
  Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and
  miscompilation
summary: >-
  Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the
  Cranelift compiler backend bit-packs SSA value indices in a way that can
  silently overflow in release builds when compiling a sufficiently large or
  specially crafted…
severity: critical
cvss: 9.9
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-197
  - CWE-843
vendor: bytecodealliance
product: wasmtime
affected:
  - wasmtime < 36.0.19
  - 'wasmtime >= 37.0.0, < 43.0.0'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-26T15:40:36.390562Z'
published: '2026-10-23'
updated: '2026-10-26'
sourceUpdated: '2026-10-26T17:42:15.319Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-115889'
references:
  - url: >-
      https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm
    label: >-
      https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm
  - url: 'https://github.com/bytecodealliance/wasmtime/pull/12613'
    label: 'https://github.com/bytecodealliance/wasmtime/pull/12613'
  - url: 'https://github.com/bytecodealliance/wasmtime/pull/14818'
    label: 'https://github.com/bytecodealliance/wasmtime/pull/14818'
  - url: >-
      https://github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0
    label: >-
      https://github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0
  - url: >-
      https://github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
    label: >-
      https://github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
  - url: 'https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19'
    label: 'https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19'
  - url: 'https://github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0'
    label: 'https://github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0'
  - url: 'https://crates.io/crates/wasmtime'
  - url: 'https://rustsec.org/advisories/RUSTSEC-2026-0380.html'
  - url: 'https://github.com/bytecodealliance/wasmtime'
  - url: 'https://github.com/advisories/GHSA-897f-g5gm-fmxm'
tags:
  - cve.org
  - osv
  - rust
  - ghsa
epss: 0.00454
epssPercentile: 0.39227
aliases:
  - RUSTSEC-2026-0380
  - GHSA-897f-g5gm-fmxm
ecosystem: rust
patched:
  - wasmtime 43.0.0
ingestedAt: '2026-10-23T21:38:13.047Z'
---

## Overview

Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.

## Affected

- `wasmtime < 36.0.19`
- `wasmtime >= 37.0.0, < 43.0.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-115889)

Affected packages:

- `wasmtime >= 37.0.0, < 43.0.0`

Patched in:

- `wasmtime 43.0.0`

Source: https://osv.dev/vulnerability/RUSTSEC-2026-0380