Wasmtime HTTP Response Splitting via wasi-http
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- 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 versions 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contain a response splitting flaw in wasi-http p3 that allows guests to set unvalidated content-length headers. A malicious wasip3 guest can splice an existing body into a new response with an incorrect content-length, enabling response splitting or injection attacks. The weakness is classified as CWE-444, Inconsistent Interpretation of HTTP Requests.
Written with Claude Haiku 5.5 from the sources below · 2026-11-04
Description from the CNA
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contains a response splitting vulnerability in wasi-http p3 that allows guests to set unvalidated content-length headers. Malicious wasip3 guests can splice an existing body into a new response with an incorrect content-length to perform response splitting or injection attacks.
Why it matters now
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| bytecodealliance | wasmtime | 46.0.0 to before 48.0.7; 49.0.0 to before 49.0.4 | 48.0.7, 49.0.4 | Patch available | CNA |
- wasmtime Vendorbytecodealliance Affected 46.0.0 to before 48.0.7; 49.0.0 to before 49.0.4 Fixed in 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 48.0.7 or 49.0.4. Red Hat rates the issue Moderate, and no fix is currently available for Red Hat Connectivity Link 1 or Red Hat Enterprise Linux 10.
Written with Claude Haiku 5.5 from the sources below · 2026-11-04
- Fix · CNA wasmtime (bytecodealliance) Fixed in 48.0.7, 49.0.4
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
bytecodealliance wasmtime 48.0.7, 49.0.4
2 records Highest priority Priority LOW 2 LOW
Other records, highest priority first
- TI-2026-84322 Wasmtime forwarded trailers skip forbidden header filteringPriority LOW 27
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: Fix deferred |
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
Timeline
- 2026-11-03 Threatist record created from CVE-2026-121439
- 2026-11-03 Alias added: GHSA-4v2q-64x5-xvrc
- 2026-11-04 Affected versions changed · Red Hat
- 2026-11-04 CVSS score added · Red Hat
- 2026-11-05 Priority changed: MEDIUM → LOW
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-2026-121439 · CVE Program
- CVE-2026-121439 · NVD
- FIRST EPSS
- GHSA-4v2q-64x5-xvrc · GitHub Advisory Database · CC BY 4.0
- CVE-2026-121439 · 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