Request smuggling in Wasmtime wasi-http through conflicting headers
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- High
- Attack requirements
- Present
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Partial Red Hat: 2 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.
Summary
Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 is affected. The wasi-http component lets a guest set multiple conflicting content-length headers (CWE-444), so the host sends HTTP requests with mismatched lengths. A malicious guest can use this to smuggle requests through servers or intermediaries that do not reject such requests.
Written with Claude Haiku 5.5 from the sources below · 2026-11-04
Description from the CNA
Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 contains a request smuggling vulnerability in wasi-http that allows guests to set multiple conflicting content-length headers. Malicious guests can make the host send HTTP requests with conflicting content-length values to smuggle requests through servers or intermediaries that do not reject them.
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 36.0.19; 37.0.0 to before 48.0.7; 49.0.0 to before 49.0.4 | 36.0.19, 48.0.7, 49.0.4 | Patch available | CNA |
- wasmtime Vendorbytecodealliance Affected before 36.0.19; 37.0.0 to before 48.0.7; 49.0.0 to before 49.0.4 Fixed in 36.0.19, 48.0.7, 49.0.4 Patch available CNA
CPE names Threatist (inferred) · 1
Inferred from how NVD named this product before; not given by a source.
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:*:*:* | — | — | bytecodealliance |
- cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:*:*:* Versions — — ·bytecodealliance
Remediation
Upgrade Wasmtime to 36.0.19, 48.0.7, or 49.0.4. Red Hat lists Red Hat Connectivity Link 1 and Red Hat Enterprise Linux 10 as affected without a fix, with no plan available.
Written with Claude Haiku 5.5 from the sources below · 2026-11-04
- Fix · CNA wasmtime (bytecodealliance) Fixed in 36.0.19, 48.0.7, 49.0.4
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Connectivity Link 1 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-11-03 Threatist record created from CVE-2026-121441
- 2026-11-03 Alias added: GHSA-9ccp-mgf6-9v48
- 2026-11-03 CISA SSVC decision points changed
- 2026-11-03 Priority changed: MEDIUM → LOW
- 2026-11-04 Affected versions changed · Red Hat
- 2026-11-04 CVSS score added · Red Hat
References
More bytecodealliance vulnerabilities
- TI-2026-85541 WAMR fast interpreter loader heap overflow via constant deduplication mismatch CVSS 4.0HIGH 8.8
- TI-2024-16741 An issue in bytecodealliance wasm-micro-runtime before v.b3f728c and fixed in commit… CVSS 3.1HIGH 8.8
- TI-2024-22658 An out-of-bound memory read vulnerability was discovered in Bytecode Alliance… CVSS 3.1HIGH 7.5
- TI-2024-18300 wasm-micro-runtime (aka WebAssembly Micro Runtime or WAMR) 06df58f is vulnerable to NULL… CVSS 3.1HIGH 7.5
- TI-2023-26034 An heap overflow vulnerability was discovered in Bytecode alliance wasm-micro-runtime… CVSS 3.1HIGH 7.5
- TI-2025-33969 WebAssembly Micro Runtime's `--addr-pool` option allows all IPv4 addresses when subnet mask is not specified CVSS 4.0MEDIUM 6.9
Sources
- CVE-2026-121441 · CVE Program
- CVE-2026-121441 · NVD
- FIRST EPSS
- GHSA-9ccp-mgf6-9v48 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-121441 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences