CVE-2026-27572
Wasmtime can panic when adding excessive fields to a `wasi:http/types.fields` instance
Impact
### 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 * [Limitations of `http::HeaderMap`](https://docs.rs/http/1.4.0/http/header/#limitations)
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rust | wasmtime | < 24.0.6 | 24.0.6 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Bytecodealliance | Wasmtime | before 24.0.6 from 25.0.0 before 36.0.6 from 37.0.0 before 40.0.4 from 41.0.0 before 41.0.4 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://docs.rs/http/1.4.0/http/header/#limitations
- 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://github.com/advisories/GHSA-243v-98vx-264h
- https://nvd.nist.gov/vuln/detail/CVE-2026-27572
- https://rustsec.org/advisories/RUSTSEC-2026-0021.html