A logic flaw in rfc3161-client's extraction of the leaf certificate from an unordered PKCS#7 bag allows an attacker to forge a certificate that matches the required common name and Extended Key Usage attributes. The library then verifies the authorization rules against the forged certificate while still validating the cryptographic signature against a legitimate trusted TimeStamping Authority. This bypasses the intended TSA authorization pinning and enables an attacker to impersonate a trusted TSA, potentially creating or claiming forged timestamps.

The vulnerability affects the rfc3161-client library distributed by trailofbits. Any installation of rfc3161-client prior to version 1.0.6 is susceptible. No additional product or version specifics are provided beyond the 1.0.6 release threshold.

With a CVSS score of 6.2 the weakness presents a moderate severity risk. EPSS data is not available and the vulnerability is not listed in the CISA KEV catalog, indicating a lower public exploitation footprint. The attack likely requires control over the PKCS#7 signature input, allowing an attacker to inject a crafted certificate chain that satisfies the TSA verification logic. Once the forged certificate is accepted, an attacker can forge timestamps that appear valid to downstream consumers of the timestamp service.