Executive brief
Sigstore Java, a library used for verifying the authenticity of software artifacts, contains a flaw where it fails to properly check the timing of digital signatures against security certificates. In practice, this could allow a malicious actor who has previously stolen a user's temporary signing key to reuse an old, expired certificate to sign new files without authorization. This undermines the security guarantees of the signing process, potentially allowing unauthorized software to appear as if it were legitimately signed.
Technical details
A regression in sigstore-java version 2.0.0, introduced in PR #1008, removed the mandatory verification of the 'integratedTime' from Rekor V1 Log Entries against the validity window of Fulcio certificates. This violates the Sigstore verification specification, which requires that the time of entry into the transparency log falls within the certificate's lifetime. An attacker with access to a previously exfiltrated temporary private key could exploit this to sign artifacts using an old certificate that should no longer be trusted. The issue is resolved in version 2.1.0 by re-implementing the integrated time check in the KeylessVerifier component.
Affected products
- sigstore sigstore-java 2.0.0
Timeline
- 2025-07-17: other: Vulnerability introduced in PR #1008
- 2026-05-07: patched: Fix merged in PR #1185
- 2026-05-26: disclosed
- 2026-06-30: advisory
References
- https://github.com/sigstore/sigstore-java/security/advisories/GHSA-qqw8-7c2r-jxch
- https://github.com/sigstore/sigstore-java/pull/1008
- https://github.com/sigstore/sigstore-java/pull/1185
- https://github.com/sigstore/sigstore-java/commit/4b7a49ebb1813f5b1ff113bcad63246358222d61
- https://github.com/sigstore/sigstore-java/commit/b529335728fc5cfb574161b4b3c06859a8a2aa88
- https://api.github.com/repos/sigstore/sigstore-java/security-advisories/GHSA-qqw8-7c2r-jxch