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CVE-2026-39395: Cosign's verify-blob-attestation reports false positive when payload parsing fails
- Severity: medium (CVSS 5.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-04-07 · updated 2026-07-24
- Weakness: CWE-754
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.
Affected products
- sigstore cosign: before 2.6.3; from 3.0.0 before 3.0.6 — fixed in 2.6.3, 3.0.6
How to fix
Upgrade to a fixed version: sigstore cosign 2.6.3, 3.0.6. Check the vendor advisory for mitigations.
References
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