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Vulnerability · Published Oct 23, 2026 · Assigned by GitHub_M

CVE-2026-115889Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation

Critical 9.9

In plain English

A critical-severity type confusion in wasmtime from bytecodealliance. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.9Critical
Exploit odds (30 days)0.5%top 60.4% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack tooling1Public PoC

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:13rust-wasmtimeno fix listedDEBIAN-CVE-2026-115889
Debian:14rust-wasmtime36.0.20+dfsg-1DEBIAN-CVE-2026-115889
Ubuntu:24.04:LTSrust-wasmtimeno fix listedUBUNTU-CVE-2026-115889
Ubuntu:26.04:LTSrust-wasmtimeno fix listedUBUNTU-CVE-2026-115889
Ubuntu:26.10rust-wasmtimeno fix listedUBUNTU-CVE-2026-115889

Affected products (as reported)

VendorProductVersions
bytecodealliance wasmtime < 36.0.19>= 37.0.0, < 43.0.0

Weakness: CWE-197, CWE-843 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

References