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VulnerabilityPublished

CVE-2026-33753: trailofbits rfc3161-client · Improper Certificate Validation

Affects trailofbits rfc3161-clientSource CVE Database V5

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Not known to be exploited · CVSS 6.2 Medium : upgrade to 1.0.6 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score
6.2Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.0.6
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 8 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade trailofbits rfc3161-client to 1.0.6.

Affected software

ProductAffectedFixed in
trailofbitsrfc3161-clientAffected
  • <1.0.6
Fixed in
  • 1.0.6
PyPIrfc3161-clientpkg:pypi/rfc3161-clientOther threatsAffected
  • <1.0.6
Fixed in
  • 1.0.6

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade rfc3161-client to version 1.0.6 or later, where this vulnerability is fixed. Patch status is not explicitly stated beyond this version update, so users should verify they are running 1.0.6 or newer. No other mitigations are indicated by the vendor advisory.

Description

CVE-2026-33753 is an authorization bypass vulnerability in the rfc3161-client Python library prior to version 1.0.6. The flaw arises from improper certificate validation during signature verification, allowing an attacker to impersonate a trusted Time-Stamping Authority (TSA). This is achieved by exploiting a logic error in extracting the leaf certificate from an unordered PKCS#7 certificate bag, enabling the attacker to append a spoofed certificate that meets the required common_name and Extended Key Usage (EKU) criteria. The library then incorrectly validates authorization rules against the forged certificate while verifying the cryptographic signature against a legitimate TSA certificate, bypassing TSA authorization pinning. The vulnerability has a CVSS 3.1 score of 6.2 (medium severity) and is fixed in version 1.0.

References

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