CVE-2026-126406
Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-Length
CVE-2026-126406 is a medium vulnerability (CVSS 6.3) in Bytecodealliance Wasmtime, published October 29, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.25%, the 16th percentile. Fixed in wasmtime-wasi-http 36.0.20.
- Severity
- 6.3 MediumCVSS 4.0, CVE List
- Exploit chance
- 0.25%EPSS, 16th percentile
- Exploitation
- None knownNot on CISA’s or ENISA’s lists
- Fixed in
36.0.20wasmtime-wasi-http +3 more
Description
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
wasmtime-wasi-httpcrates.io | 0.0.0-0 up to 36.0.20, 37.0.0 up to 48.0.8, 49.0.0 up to 49.0.5, 50.0.0 up to 50.0.1 | 36.0.2048.0.849.0.550.0.1 |
rust-wasmtimeUbuntu:24.04:LTS | All versions, plus listed versions 10.0.1+dfsg-715.0.1+dfsg-416.0.0+dfsg-216.0.0+dfsg-3 | None known |
rust-wasmtimeUbuntu:26.10 | All versions, plus listed versions 36.0.5+dfsg-136.0.13+dfsg-1 | None known |
rust-wasmtimeUbuntu:26.04:LTS | All versions, plus listed versions 26.0.1+dfsg-326.0.1+dfsg-428.0.1+dfsg-329.0.1+dfsg-536.0.5+dfsg-1 | None known |
What each source reports
CVE List Score used
Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-Length
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.
- Record
CVE-2026-126406- CVSS 4.0
- 6.3 Medium
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 - CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-444
- Updated
- 2026-11-13
EUVDEUVD-2026-125159
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.
- Record
EUVD-2026-125159- CVSS 4.0
- 6.3 Medium
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 - Updated
- 2026-11-13
GitHub AdvisoriesGHSA-xhgr-wvjp-62fm
The wasmtime-wasi-http p2 implementation in Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0...
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.
- Record
GHSA-xhgr-wvjp-62fm- CVSS 4.0
- 6.3 Medium
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 - CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-444
- Updated
- 2026-11-13
NVD
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.
- Record
CVE-2026-126406- CVSS 4.0
- 6.3 Medium
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 - CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-444
- Updated
- 2026-11-13
OSV
Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-Length
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.
- Record
CVE-2026-126406- CVSS 4.0
- 6.3 Medium
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 - Weakness
- CWE-444
- Updated
- 2026-11-14
OSVRUSTSEC-2026-0421
wasi-http p2: outgoing content-length can be invalid or not match body
This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-h4wp-g4x3-7398 For more information see the GitHub-hosted security advisory.
- Record
RUSTSEC-2026-0421- CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-14
OSVUBUNTU-CVE-2026-126406
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.
- Record
UBUNTU-CVE-2026-126406- CVSS 4.0
- 6.3 Medium
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 - CVSS 3.1
- 3.7 Low
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-13
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, aliases, facts, published, references | OSV | |
| affected, aliases, published, references | OSV | |
| published | EUVD | |
| published | EUVD | |
| aliases, references | GitHub Advisories, NVD | |
| aliases, published | EUVD | |
| first indexed | CVE List | |
| first indexed | OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
References
github.com/bytecodealliance/wasmtime/security/advisories/GHSA-h4wp-g4x3-7398
vulncheck.com/advisories/wasmtime-before-36.0.20-http-request-smuggling-via-wasi-http-p2-content-length
nvd.nist.gov/vuln/detail/CVE-2026-126406
crates.io/crates/wasmtime-wasi-http