Vulnerability 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 Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Linuxfoundation | Sigstore Timestamp Authority | < 2.0.6 |
Related Weaknesses (CWE)
References
- https://github.com/sigstore/timestamp-authority/releases/tag/v2.0.6ProductRelease Notes
- https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgMitigationVendor Advisory
FAQ
What is CVE-2026-39984?
CVE-2026-39984 is a vulnerability with a CVSS score of 5.5 (MEDIUM). 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. VerifyTimesta...
How severe is CVE-2026-39984?
CVE-2026-39984 has been rated MEDIUM with a CVSS base score of 5.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-39984?
Check the references section above for vendor advisories and patch information. Affected products include: Linuxfoundation Sigstore Timestamp Authority.