How severe is CVE-2026-33753?

CVE-2026-33753 has a CVSS 3.x base score of 6.2, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-33753 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (9th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33753?

CVE-2026-33753 affects Trailofbits Rfc3161-client. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33753?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-33753 have an EU (EUVD) identifier?

Yes. CVE-2026-33753 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-20480.

When was CVE-2026-33753 published?

CVE-2026-33753 was published on 2026-04-08 and last updated on 2026-06-17.

CVE-2026-33753

CVE-2026-33753 is a medium-severity vulnerability in Trailofbits Rfc3161-client with a CVSS 3.x base score of 6.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-295.

Key facts

Severity: Medium (CVSS 3.x base score 6.2)
EPSS exploit prediction: 0% (9th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-20480
Weakness: CWE-295
Affected product: Trailofbits Rfc3161-client
Published: 2026-04-08
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-33753?: 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.
How severe is CVE-2026-33753?: CVE-2026-33753 has a CVSS 3.x base score of 6.2, rated medium severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-33753 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (9th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33753?: CVE-2026-33753 affects Trailofbits Rfc3161-client. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33753?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33753 have an EU (EUVD) identifier?: Yes. CVE-2026-33753 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-20480.
When was CVE-2026-33753 published?: CVE-2026-33753 was published on 2026-04-08 and last updated on 2026-06-17.

References

https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-3xxc-pwj6-jgrj

Affected products (1)

cpe:2.3:a:trailofbits:rfc3161-client:*:*:*:*:*:*:*:*

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