CVE-2026-39395

Cosign's verify-blob-attestation reports false positive when payload parsing fails

State: Published
Severity: 4.3 Medium
Published: Apr 7, 2026
Updated: Apr 8, 2026
Reserved: Apr 6, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	4.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N	GitHub_M

Weaknesses

CWE-754 Improper Check for Unusual or Exceptional Conditions

Affected Products

Product	Versions
cosignsigstore	>= 3.0.0, < 3.0.6Affected < 2.6.3Affected

References

https://github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6

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