JLSEC-2026-1353 Medium 6.9
Wasmtime can panic when adding excessive fields to a `wasi:http/types.fields` instance
Impact
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.
Patches
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.
Workarounds
There are no known workarounds at this time, embedders are encouraged to update to a patched version of Wasmtime.
Resources
References
- https://docs.rs/http/1.4.0/http/header/#limitations
- https://github.com/advisories/GHSA-243v-98vx-264h
- https://github.com/bytecodealliance/wasmtime/commit/301dc7162cca51def19131019af1187f45901c0a
- https://github.com/bytecodealliance/wasmtime/releases/tag/v24.0.6
- https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.6
- https://github.com/bytecodealliance/wasmtime/releases/tag/v40.0.4
- https://github.com/bytecodealliance/wasmtime/releases/tag/v41.0.4
- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-243v-98vx-264h
- https://nvd.nist.gov/vuln/detail/CVE-2026-27572
- https://rustsec.org/advisories/RUSTSEC-2026-0021.html