CVE-2026-39984

Aliases:GHSA-xm5m-wgh2-rrg3GO-2026-5763
Advisory lineage Upstream: 0 Downstream: 11
Analyzed
Published: 14 Apr 2026, 23:41
Last modified:16 Apr 2026, 14:00

Vulnerability Summary

Overall Risk (default)
low
22/100
CVSS Score
5.5 MEDIUM
v3.1 (cve.org)
EPSS Score
0.1% LOW
0% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

14 Apr 2026, 23:41
Published
Vulnerability first disclosed
16 Apr 2026, 14:00
Last Modified
Vulnerability information updated

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 Metrics

  • v3.1•MEDIUM•Score: 5.5CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS Trends

Current EPSS score: 0.10%• Percentile: 1%

Techniques & Countermeasures

  • CWE-295•Improper Certificate Validation

    The product does not validate, or incorrectly validates, a certificate.

Affected Systems

  • github.com/sigstore•timestamp-authority

    all

  • github.com/sigstore/timestamp-authority•v2

    < 2.0.6

  • linuxfoundation•sigstore_timestamp_authority

    < 2.0.6

  • sigstore•timestamp-authority

    < 2.0.6

References (4)