PYSEC-2026-525
rfc3161-client has insufficient verification for timestamp response signatures
Quick fix
PYSEC-2026-525 — rfc3161-client: upgrade to the fixed version with the command below.
pip install --upgrade 'rfc3161-client>=1.0.3'Details
### Impact
`rfc3161-client` 1.0.2 and earlier contain a flaw in their timestamp response signature verification logic. In particular, it performs chain verification against the TSR's embedded certificates up to the trusted root(s), but fails to verify the TSR's own signature against the timestamping leaf certificates. Consequently, vulnerable versions perform insufficient signature validation to properly consider a TSR verified, as the attacker can introduce _any_ TSR signature so long as the embedded leaf chains up to some root TSA.
### Patches
Users should immediately upgrade to `rfc3161-client` 1.0.3 or later.
### Workarounds
There is no workaround possible. Users should immediately upgrade to a fixed version.
Are you affected?
Enter the version of the package you're using.
Affected packages
References
- https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-6qhv-4h7r-2g9m[WEB]
- https://nvd.nist.gov/vuln/detail/CVE-2025-52556[ADVISORY]
- https://github.com/trailofbits/rfc3161-client/commit/724a184f953e3f171f85cb223871172b41b0d0dc[WEB]
- https://github.com/trailofbits/rfc3161-client[PACKAGE]
- https://pypi.org/project/rfc3161-client[PACKAGE]
- https://github.com/advisories/GHSA-6qhv-4h7r-2g9m[ADVISORY]