CVE-2026-126406 json
Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-Length
published 16d ago modified yesterday also EUVD-2026-125159 , GHSA-h4wp-g4x3-7398 , RUSTSEC-2026-0421
- cvss
- 3.7
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.2%
- EPSS 0.2% chance of exploitation in 30 days, percentile 16%
- public exploits
- 0
- none known
Summary
The wasmtime-wasi-http p2 implementation in Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 can send conflicting content-length headers, or ones not matching the body, in outgoing requests. A guest that reuses a received response's headers resource to send a bodyless request can enable request smuggling against non-compliant servers, potentially bypassing embedder destination access controls.
Patch / fix
- crates.io wasmtime-wasi-http 36.0.20, 48.0.8, 49.0.5, 50.0.1
- bytecodealliance wasmtime 36.0.20, 48.0.8, 49.0.5, 50.0.1
- github.com/bytecodealliance/wasmtime#15070 pull request
Is CVE-2026-126406 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerExploit prediction
0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-14).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 6.3 | CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N |
| CNA | 3.1 | 3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N |
| CNA | 4.0 | 6.3 | CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
| NVD | 3.1 | 3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N |
| OSV | 3.1 | 3.7 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| crates.io | wasmtime-wasi-http | >=0.0.0-0, <36.0.20 >=37.0.0, <48.0.8 >=49.0.0, <49.0.5 >=50.0.0, <50.0.1 |
36.0.20 48.0.8 49.0.5 50.0.1 |
Affected products
- bytecodealliance wasmtime
Classification
- Weakness
-
- CWE-444 Inconsistent Interpretation of HTTP Requests
References
-
github.com
/bytecodealliance/wasmtime/pull/15070
web
-
github.com
/bytecodealliance/wasmtime/security/advisories/GHSA-h4wp-g4x3-7398
vendor-advisory, advisory
-
vulncheck.com
/advisories/wasmtime-before-36.0.20-http-request-smuggling-via-wasi-http-p2-content-length
third-party-advisory
-
crates.io
/crates/wasmtime-wasi-http
package
-
rustsec.org
/advisories/RUSTSEC-2026-0421.html
advisory
Sources
- CVE List CVE-2026-126406
- NVD CVE-2026-126406
- OSV RUSTSEC-2026-0421
- Maintainer advisory GHSA-h4wp-g4x3-7398
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of bytecodealliance/wasmtime published their own advisory on GitHub. Reviewed sources take precedence over it.