CVE-2026-33753

6.2 MEDIUM 0.2% exploit odds Fix listed Crypto Library

What it is

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.

At a glance

Exploitability: Can be exploited locally on the machine without logging in. High risk of data tampering.
Exploit odds: 0.2% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-04-08 16:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-07-24 23:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.2% in the next 30 days (EPSS).
Severity: 6.2 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-04-08 16:16 UTC
Last modified: 2026-07-24 23:10 UTC
Exploit probability: 0.2% · EPSS, next 30 days
Weakness: CWE-295 · Improper certificate validation
Record status: Analyzed

Affected

Trailofbits rfc3161-client < 1.0.6

Attack profile CVSS 3.1 · 6.2

Attack vector: Local
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Raw vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Is it in your code?

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Read https://cve-list.com/agent/cve/CVE-2026-33753.md and follow it. Check whether this project is affected by CVE-2026-33753. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record