Wasmtime can panic when adding excessive fields to a `wasi:http/types.fields` instance
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- Passive
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 1 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-770.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| bytecodealliance | wasmtime | before 24.0.6; 25.0.0 to before 36.0.6; 37.0.0 to before 40.0.4; 41.0.0 to before 41.0.4 | 24.0.6, 36.0.6, 40.0.4, 41.0.4 | Patch available | CNA |
| — | wasmtime (crates.io) | before 24.0.6 | 24.0.6 | Patch available | GHSA-243v-98vx-264h |
| — | wasmtime (crates.io) | 25.0.0 to before 36.0.6 | 36.0.6 | Patch available | GHSA-243v-98vx-264h |
| — | wasmtime (crates.io) | 37.0.0 to before 40.0.4 | 40.0.4 | Patch available | GHSA-243v-98vx-264h |
- wasmtime Vendorbytecodealliance Affected before 24.0.6; 25.0.0 to before 36.0.6; 37.0.0 to before 40.0.4; 41.0.0 to before 41.0.4 Fixed in 24.0.6, 36.0.6, 40.0.4, 41.0.4 Patch available CNA
- wasmtime (crates.io) Vendor— Affected before 24.0.6 Fixed in 24.0.6 Patch available GHSA-243v-98vx-264h
- wasmtime (crates.io) Vendor— Affected 25.0.0 to before 36.0.6 Fixed in 36.0.6 Patch available GHSA-243v-98vx-264h
- wasmtime (crates.io) Vendor— Affected 37.0.0 to before 40.0.4 Fixed in 40.0.4 Patch available GHSA-243v-98vx-264h
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:* | before 24.0.6; 25.0.0 to before 36.0.6; 37.0.0 to before 40.0.4; 41.0.0 to before 41.0.4 | Vulnerable | bytecodealliance |
- cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:* Versions before 24.0.6; 25.0.0 to before 36.0.6; 37.0.0 to before 40.0.4; 41.0.0 to before 41.0.4 Vulnerable ·bytecodealliance
Remediation
- Fix · CNA wasmtime (bytecodealliance) Fixed in 24.0.6, 36.0.6, 40.0.4, 41.0.4
- Fix · GHSA-243v-98vx-264h wasmtime (crates.io) Fixed in 24.0.6 Advisory →
- Fix · GHSA-243v-98vx-264h wasmtime (crates.io) Fixed in 36.0.6 Advisory →
- Fix · GHSA-243v-98vx-264h wasmtime (crates.io) Fixed in 40.0.4 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Connectivity Link 1 | Affected | No fix yet |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-27572
- 2026-10-03 Alias added: GHSA-243v-98vx-264h
- 2026-10-06 EPSS moved to the 50th–90th percentile
- 2026-10-25 EPSS moved to the below the 50th percentile
References
Advisory 2
Other 7
- https://docs.rs/http/1.4.0/http/header/#limitations
- 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
- https://rustsec.org/advisories/RUSTSEC-2026-0021.html
More bytecodealliance Wasmtime vulnerabilities
- TI-2026-21632 Wasmtime is vulnerable to panic when dropping a `[Typed]Func::call_async` future CVSS 4.0MEDIUM 6.9
- TI-2023-11636 Guest-controlled out-of-bounds read/write on x86_64 in wasmtime CVSS 3.1CRITICAL 10.0
- TI-2022-18765 Wasmtime vulnerable to data leakage between instances in the pooling allocator CVSS 3.1HIGH 8.6
- TI-2022-08604 Use after free in Wasmtime CVSS 3.1CRITICAL 9.8
- TI-2022-18766 wasmtime_trap_code C API function has out of bounds write vulnerability CVSS 3.1CRITICAL 9.8
- TI-2026-27209 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access CVSS 4.0CRITICAL 9.0
Sources
- CVE-2026-27572 · CVE Program
- CVE-2026-27572 · NVD
- FIRST EPSS
- GHSA-243v-98vx-264h · GitHub Advisory Database · CC BY 4.0
- CVE-2026-27572 · Red Hat security data · CC BY 4.0
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