All vulnerabilities
CVE-2026-115889GHSA-897f-g5gm-fmxmRUSTSEC-2026-0380

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

bytecodealliance wasmtimerustLibraries & packages
Open in ThreatlineRecord JSON
CVSS
9.9Critical
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)No scoreNo FIRST EPSS score in this snapshot yet
Fixed in36.0.19Also 43.0.0GitHub
Published23 Oct 2026Updated 23 Oct 2026CVE List

What fixes it

  • 36.0.19wasmtime, rustGitHub
  • 43.0.0wasmtime, rustGitHub
  • 36.0.19wasmtime, crates.ioOSVcargo update -p wasmtime --precise 36.0.19
  • 43.0.0wasmtime, crates.ioOSVcargo update -p wasmtime --precise 43.0.0

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Reports 1

1 outlet mention it. Reports are not confirmation; each links to its source.

Description

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.

Text from GitHub Advisory Database

Affected versions 6

  • wasmtime, rust< 36.0.19GitHub
  • wasmtime, rust>= 37.0.0, < 43.0.0GitHub
  • wasmtimeaffected: < 36.0.19CVE List
  • wasmtimeaffected: >= 37.0.0, < 43.0.0CVE List
  • wasmtime, crates.iofrom first release, fixed in 36.0.19OSV
  • wasmtime, crates.iofrom 37.0.0, fixed in 43.0.0OSV

References 9