trailofbits rfc3161-client up to 1.0.5 Time-Stamp Protocol certificate validation

Summaryinfo

A vulnerability was found in trailofbits rfc3161-client up to 1.0.5. It has been declared as critical. The impacted element is an unknown function of the component Time-Stamp Protocol Handler. Such manipulation leads to certificate validation. This vulnerability is traded as CVE-2026-33753. An attack has to be approached locally. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in trailofbits rfc3161-client up to 1.0.5. It has been rated as problematic. Affected by this issue is some unknown processing of the component Time-Stamp Protocol Handler. The manipulation with an unknown input leads to a certificate validation vulnerability. Using CWE to declare the problem leads to CWE-295. The product does not validate, or incorrectly validates, a certificate. Impacted is integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-33753 since 03/23/2026. The exploitation is known to be difficult. The attack needs to be approached locally. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1587.003.

Upgrading to version 1.0.6 eliminates this vulnerability.

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Productinfo

Type

• Application Server Software

Vendor

• trailofbits

Name

• rfc3161-client

Version

• 1.0.0
• 1.0.1
• 1.0.2
• 1.0.3
• 1.0.4
• 1.0.5

Website

• Product: https://github.com/trailofbits/rfc3161-client/

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