CVE-2026-39984: Sigstore Timestamp Authority has Improper Certificate Validation in verifier
CVE-2026-39984 · Severity: medium · CVSS 5.5 · Published 2026-04-15
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.
Yes. github.com/sigstore/timestamp-authority/v2 (Go): upgrade to 2.0.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-39984?
Check whether you run github.com/sigstore/timestamp-authority (Go), github.com/sigstore/timestamp-authority/v2 (Go) or Linuxfoundation Sigstore Timestamp Authority at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
github.com/sigstore/timestamp-authority/v2 (Go): upgrade to 2.0.6 or later
go get github.com/sigstore/timestamp-authority/v2@v2.0.6