CVE-2026-39984 (GCVE-0-2026-39984)

Vulnerability from cvelistv5 – Published: 2026-04-14 23:41 – Updated: 2026-04-16 14:00
VLAI
Title
Sigstore Timestamp Authority has Improper Certificate Validation in verifier
Summary
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.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-16 14:00 UTC
CWE
  • CWE-295 - Improper Certificate Validation
Assigner
References
Impacted products
Show details on NVD website
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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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