Improper Certificate Validation Affecting rfc3161-client package, versions [1.0.1,1.0.6)

Affected versions of this package are vulnerable to Improper Certificate Validation through the Verifier._verify_leaf_certs logic in src/rfc3161_client/verify.py. An attacker can make a timestamp response from a trusted TSA verify as if it came from a different pinned TSA by injecting certificates into the PKCS#7 SignedData bag so the leaf-selection heuristic picks a forged certificate that matches the configured common_name and EKU while the signature still validates against the real TSA certificate. This lets an attacker impersonate the expected timestamp authority and cause applications to accept timestamps under the wrong TSA identity.

Notes

• The bypass depends on the response containing exactly one SignerInfo with issuerAndSerialNumber; code paths that reject responses with multiple signer infos or that do not use the SignedData certificate bag for leaf selection are not affected by this specific issue.
• The attacker needs a valid timestamp response from a TSA chain trusted by the verifier’s roots/intermediates set, plus the ability to inject extra certificates into that response; without a trusted underlying signature chain, verification still fails.

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• Maintainer's Advisory