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 21d ago modified 5d ago also GHSA-jxcf-8qw5-5c33 , RUSTSEC-2026-0377 , EUVD-2026-115862
- 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
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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
- 6d ago
Exploit prediction
0.22% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-09).
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
-
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
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