What is CVE-2026-121440?

CVE-2026-121440 is a low-severity vulnerability in Bytecodealliance Wasmtime, classified under CWE-424. CVSS score: 3.7/10. Published 2026-11-03.

How severe is CVE-2026-121440?

Low severity. CVSS v3 base score is 3.7 out of 10.

Vulnerability in Bytecodealliance Wasmtime

CVE-2026-121440

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.

Published 2026-11-03 · last modified 2026-11-03.

CVSS v3 metric

CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Bytecodealliance Wasmtime

Weakness classification (CWE)

CWE-424

References

github.com/bytecodealliance/wasmtime/security/advisories/GHSA-jxcf-8qw5-5c33 (vendor-advisory)
www.vulncheck.com/advisories/wasmtime-46.0.0-before-48.0.7-and-49.0.0-before-49… (third-party-advisory)

Frequently asked questions

What is CVE-2026-121440?: CVE-2026-121440 is a low-severity vulnerability in Bytecodealliance Wasmtime, classified under CWE-424. CVSS score: 3.7/10. Published 2026-11-03.
How severe is CVE-2026-121440?: Low severity. CVSS v3 base score is 3.7 out of 10.