{"cve":"CVE-2026-39984","nvd":{"published":"2026-04-15T04:17:40.203","modified":"2026-10-26T21:10:00.170","status":"Analyzed","description":"Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","score":5.5},"cwes":["CWE-295"],"references":["https://github.com/sigstore/timestamp-authority/releases/tag/v2.0.6","https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3"],"products":["linuxfoundation:sigstore_timestamp_authority"],"source":"nvd","synced_at":"2026-10-26T21:38:48.864438205+00:00"},"epss":{"cve":"CVE-2026-39984","score":0.00099,"percentile":0.008,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-xm5m-wgh2-rrg3","url":"https://osv.dev/vulnerability/GHSA-xm5m-wgh2-rrg3","summary":"Sigstore Timestamp Authority has Improper Certificate Validation in verifier","modified":"2026-09-10T03:50:44.895516756Z","packages":[{"ecosystem":"Go","name":"github.com/sigstore/timestamp-authority/v2","purl":"pkg:golang/github.com/sigstore/timestamp-authority/v2","ranges":["<2.0.6"],"fixed":["2.0.6"]}]},{"id":"GO-2026-5763","url":"https://osv.dev/vulnerability/GO-2026-5763","summary":"Sigstore Timestamp Authority has Improper Certificate Validation in verifier in github.com/sigstore/timestamp-authority","modified":"2026-06-26T15:44:23.064396068Z","packages":[{"ecosystem":"Go","name":"github.com/sigstore/timestamp-authority","purl":"pkg:golang/github.com/sigstore/timestamp-authority","ranges":["all versions"],"fixed":[]},{"ecosystem":"Go","name":"github.com/sigstore/timestamp-authority/v2","purl":"pkg:golang/github.com/sigstore/timestamp-authority/v2","ranges":["<2.0.6"],"fixed":["2.0.6"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}