CVE-2026-27572: Bytecodealliance Wasmtime

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

Wasmtime is a runtime for WebAssembly. Prior to versions 24.0.6, 36.0.6, 4.0.04, 41.0.4, and 42.0.0, Wasmtime's implementation of the `wasi:http/types.fields` resource is susceptible to panics when too many fields are added to the set of headers. Wasmtime's implementation in the `wasmtime-wasi-http` crate is backed by a data structure which panics when it reaches excessive capacity and this condition was not handled gracefully in Wasmtime. Panicking in a WASI implementation is a Denial of Service vector for embedders and is treated as a security vulnerability in Wasmtime. Wasmtime 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 patch this vulnerability and return a trap to the guest instead of panicking. There are no known workarounds at this time. Embedders are encouraged to update to a patched version of Wasmtime.

Affected products

• Bytecodealliance Wasmtime: before 24.0.6 (fixed in 24.0.6); from 25.0.0, before 36.0.6 (fixed in 36.0.6); from 37.0.0, before 40.0.4 (fixed in 40.0.4); from 41.0.0, before 41.0.4 (fixed in 41.0.4)

Published 2026-02-24. Last modified 2026-06-17.