CVE-2026-33753
MediumCVSS 6.2Exploitation Probability (EPSS)
Low risk9th percentile - higher than 9% of all known CVEs
Summary
The rfc3161-client library prior to version 1.0.6 contains an authorization bypass vulnerability in signature verification. An attacker can impersonate a trusted Time-Stamping Authority (TSA) by exploiting a flaw in extracting the leaf certificate from an unordered PKCS#7 certificate bag.
Risk Assessment
An attacker can forge timestamps, potentially compromising data integrity and trust in timestamp-based systems.
Recommendation
It is recommended to update the rfc3161-client library to version 1.0.6 or later.
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Original NVD description (English source)
rfc3161-client is a Python library implementing the Time-Stamp Protocol (TSP) described in RFC 3161. Prior to 1.0.6, an Authorization Bypass vulnerability in rfc3161-client's signature verification allows any attacker to impersonate a trusted TimeStamping Authority (TSA). By exploiting a logic flaw in how the library extracts the leaf certificate from an unordered PKCS#7 bag of certificates, an attacker can append a spoofed certificate matching the target common_name and Extended Key Usage (EKU) requirements. This tricks the library into verifying these authorization rules against the forged certificate while validating the cryptographic signature against an actual trusted TSA (such as FreeTSA), thereby bypassing the intended TSA authorization pinning entirely. This vulnerability is fixed in 1.0.6.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS