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

bytecodealliance wasmtime · CVE-2026-115889 EUVD-2026-109186 GHSA-897F-G5GM-FMXM
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Assessment: Track

SSVC decision points: exploitation none, automatable no, technical impact total, deployment low.

What is it?

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.

Evidence

No coverage recorded yet.

Exploitation

  • Public proof of concept
  • Exploited in the wild
  • Listed as known exploited
CVSS
9.9
EPSS
–
First seen
3 h ago
Status
corroborated

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