CVE-2026-121440 json
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 Forwarded Trailers Header Filter Bypass
published 24d ago modified 9d ago also EUVD-2026-115862 , GHSA-jxcf-8qw5-5c33 , RUSTSEC-2026-0377
- 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 13%
- public exploits
- 0
- none known
Summary
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 fails to check forwarded trailers against the WasiHttpHooks::is_forbidden_header hook in wasi-http p3. WASIp3 guests can forward a request or response body so its trailers skip embedder-customized forbidden header filtering, undermining header restrictions the embedder intended.
Patch / fix
- crates.io wasmtime-wasi-http 48.0.7, 49.0.4
- bytecodealliance wasmtime 48.0.7, 49.0.4
- github.com/bytecodealliance/wasmtime#14823 pull request
Is CVE-2026-121440 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 FencerVendor advisories
What the vendors themselves say about their products: affected, fixed or not affected, and what to do.
red hat product security vex CVE-2026-121440 updated cvss 3.7
wasmtime: Wasmtime: Header restriction bypass via forwarded HTTP trailers
-
Red Hat Connectivity Link 1 rhcl-1/wasm-shim-rhel9 Red Hat Enterprise Linux 10 tree-sitter 0.23.0-3.el10, virt-firmware-rs 26.4-1.el10affected: no fix available “Fix deferred”
Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 9d ago
Exploit prediction
0.22% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-12).
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 |
| 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 | >=46.0.0, <48.0.7 >=49.0.0, <49.0.4 |
48.0.7 49.0.4 |
Affected products
- bytecodealliance wasmtime
Classification
- Weakness
-
- CWE-424 Improper Protection of Alternate Path
References
-
github.com
/bytecodealliance/wasmtime/pull/14823
web
-
github.com
/bytecodealliance/wasmtime/security/advisories/GHSA-jxcf-8qw5-5c33
vendor-advisory, advisory
-
vulncheck.com
/advisories/wasmtime-46.0.0-before-48.0.7-and-49.0.0-before-49.0.4-forwarded-trailers-header-filter-bypass
third-party-advisory
-
crates.io
/crates/wasmtime-wasi-http
package
-
rustsec.org
/advisories/RUSTSEC-2026-0377.html
advisory
Sources
- CVE List CVE-2026-121440
- NVD CVE-2026-121440
- OSV RUSTSEC-2026-0377
- Maintainer advisory GHSA-jxcf-8qw5-5c33
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.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.