What is CVE-2026-39395?

CVE-2026-39395 is a medium-severity vulnerability in Sigstore Cosign, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 4.3/10. Published 2026-04-07.

How severe is CVE-2026-39395?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Sigstore Cosign

CVE-2026-39395

Cosign provides code signing and transparency for containers and binaries. Prior to 3.0.6 and 2.6.3, cosign verify-blob-attestation may erroneously report a "Verified OK" result for attestations with malformed payloads or mismatched predicate types. For old-format bundles and detached signatures, this was due to a logic flaw in the error handling of the predicate type validation. For new-format bundles, the predicate type validation was bypassed completely. This vulnerability is fixed in 3.0.6 and 2.6.3.

Published 2026-04-07 · last modified 2026-07-24.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (19.6th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 20th percentile — 19.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Sigstore Cosign — versions >= 3.0.0, < 3.0.6, < 2.6.3

Weakness classification (CWE)

CWE-754 — Improper Check for Unusual or Exceptional Conditions

References

github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6 (Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-39395?: CVE-2026-39395 is a medium-severity vulnerability in Sigstore Cosign, classified under Improper Check for Unusual or Exceptional Conditions. CVSS score: 4.3/10. Published 2026-04-07.
How severe is CVE-2026-39395?: Medium severity. CVSS v3 base score is 4.3 out of 10.