---
title: "CVE-2025-52556: rfc3161-client has insufficient verification for timestamp response signatures"
url: https://erroneo.us/security/cve/CVE-2025-52556/
description: "CVE-2025-52556 (rfc3161-client (PyPI)): rfc3161-client is a Python library implementing the Time-Stamp Protocol (TSP) described in RFC 3161. Prior to…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-06-21
date_modified: 2025-06-27
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-52556"
kev: false
cvss: 9.3
epss: 0.00169
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-52556: rfc3161-client has insufficient verification for timestamp response signatures

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.2% , percentile 6: FIRST’s model estimates a 0.2% chance of exploitation activity in the next 30 days, higher than 6% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes rfc3161-client (PyPI) <= 1.0.2, fixed in 1.0.3 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- PyPI `rfc3161-client` <= 1.0.2 → fixed: 1.0.3

## Affected products (CVE record)

- trailofbits rfc3161-client: < 1.0.3

## Severity

- GitHub_M CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`
- GitHub CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.17% probability of exploitation activity in the next 30 days; percentile 6.

## Sources

- [GitHub Advisory GHSA-6qhv-4h7r-2g9m](https://github.com/advisories/GHSA-6qhv-4h7r-2g9m)
- [CVE.org record CVE-2025-52556](https://www.cve.org/CVERecord?id=CVE-2025-52556)
- [NVD entry CVE-2025-52556](https://nvd.nist.gov/vuln/detail/CVE-2025-52556)
- [github.com](https://github.com/trailofbits/rfc3161-client/security/advisories/GHSA-6qhv-4h7r-2g9m)
- [github.com](https://github.com/trailofbits/rfc3161-client/commit/724a184f953e3f171f85cb223871172b41b0d0dc)

---
Source page: https://erroneo.us/security/cve/CVE-2025-52556/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt