How severe is CVE-2025-52556?

CVE-2025-52556 has a CVSS 4.0 base score of 9.3, rated critical severity.

Is CVE-2025-52556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2025-52556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2025-52556 have an EU (EUVD) identifier?

Yes. CVE-2025-52556 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-18798.

When was CVE-2025-52556 published?

CVE-2025-52556 was published on 2025-06-21 and last updated on 2026-06-17.

CVE-2025-52556

CVE-2025-52556 is a critical-severity vulnerability with a CVSS 4.0 base score of 9.3. 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-347.

Key facts

Severity: Critical (CVSS 4.0 base score 9.3)
EPSS exploit prediction: 0% (4th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-18798
Weakness: CWE-347
Published: 2025-06-21
Last modified: 2026-06-17

Description

rfc3161-client is a Python library implementing the Time-Stamp Protocol (TSP) described in RFC 3161. Prior to version 1.0.3, there is a flaw in the timestamp response signature verification logic. In particular, chain verification is performed against the TSR's embedded certificates up to the trusted root(s), but fails to verify the TSR's own signature against the timestamping leaf certificates. Consequently, vulnerable versions perform insufficient signature validation to properly consider a TSR verified, as the attacker can introduce any TSR signature so long as the embedded leaf chains up to some root TSA. This issue has been patched in version 1.0.3. There is no workaround for this issue.

Frequently asked questions

What is CVE-2025-52556?: rfc3161-client is a Python library implementing the Time-Stamp Protocol (TSP) described in RFC 3161. Prior to version 1.0.3, there is a flaw in the timestamp response signature verification logic. In particular, chain verification is performed against the TSR's embedded certificates up to the trusted root(s), but fails to verify the TSR's own signature against the timestamping leaf certificates. Consequently, vulnerable versions perform insufficient signature validation to properly consider a TSR verified, as the attacker can introduce any TSR signature so long as the embedded leaf chains up to some root TSA. This issue has been patched in version 1.0.3. There is no workaround for this issue.
How severe is CVE-2025-52556?: CVE-2025-52556 has a CVSS 4.0 base score of 9.3, rated critical severity.
Is CVE-2025-52556 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (4th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2025-52556?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2025-52556 have an EU (EUVD) identifier?: Yes. CVE-2025-52556 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-18798.
When was CVE-2025-52556 published?: CVE-2025-52556 was published on 2025-06-21 and last updated on 2026-06-17.

References

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