{"id":"CVE-2026-39395","aliases":["BIT-cosign-2026-39395","GHSA-w6c6-c85g-mmv6","GO-2026-5694"],"url":"https://o3.security/vulnerability/CVE-2026-39395","summary":"Cosign's verify-blob-attestation reports false positive when payload parsing fails","details":"## Description\n\n`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.\n\n## Impact\n\nWhen `cosign verify-blob-attestation` is used without `--check-claims` set to `true`, an attestation that has a valid signature but a malformed or unparsable payload would be incorrectly validated. Additionally, systems relying on `--type <predicate type>` to reject attestations with mismatched types would be lead to trust the unexpected attestation type.\n\n## Patches\n\nv3.0.6, v2.6.3\n\n## Workarounds\n\nAlways set `--check-claims=true` for attestation verification.","published":"2026-04-07T20:06:28.798Z","modified":"2026-08-12T03:51:12.147593249Z","cvss":{"score":4.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/sigstore/cosign","fixedVersion":"3.0.6"},{"ecosystem":"Go","name":"github.com/sigstore/cosign","fixedVersion":"2.6.3"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39395.json"},{"type":"ADVISORY","url":"https://github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-39395"},{"type":"PACKAGE","url":"https://github.com/sigstore/cosign"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:12.147593249Z"}}