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Fencer Vulns
high 7.5

CVE-2025-61920 json

Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

published 2025-10-10 12 mo ago modified 2026-10-19 20 d ago also EUVD-2025-33768 , GHSA-pq5p-34cr-23v9 , PYSEC-2026-1203

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 50%
public exploits
0
none known

Summary

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.5, Authlib’s JOSE implementation accepts unbounded JWS/JWT header and signature segments. A remote attacker can craft a token whose base64url‑encoded header or signature spans hundreds of megabytes. During verification, Authlib decodes and parses the full input before it is rejected, driving CPU and memory consumption to hostile levels and enabling denial of service. Version 1.6.5 patches the issue. Some temporary workarounds are available. Enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.

Patch / fix

  • pypi authlib 1.6.5
  • authlib authlib 1.6.5
  • python-authlib Debian 12 1.2.0-1+deb12u1
  • python-authlib Debian 13 1.6.0-1+deb13u1
  • python-authlib Debian 14 1.6.5-1

debian advisories DEBIAN-CVE-2025-61920

  • python-authlib Ubuntu Pro 22.04 LTS 0.15.5-1ubuntu0.1~esm1
  • python-authlib Ubuntu Pro 24.04 LTS 1.3.0-1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2025-61920

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-Authlib SLE Module for Python 3 15 SP7, SLE Module for Python 3 15 SP6, openSUSE Leap 15.6 1.3.1-150600.3.6.1

suse advisories SUSE-SU-2025:3754-1

  • python-Authlib openSUSE Tumbleweed 1.6.5-1.1

opensuse advisories openSUSE-SU-2025:15629-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-61920 updated cvss 7.5

authlib: Authlib Denial of Service

  • Red Hat Quay 3.9 quay 3.9-1764254756, quay 3.9-1765382758
    fixed: vendor fix “Users unable to upgrade may manually enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.” RHSA-2025:23061
  • Red Hat Quay 3.10 quay 3.10.17-1764168428, quay 3.10.17-1765384144
    fixed: vendor fix “Users unable to upgrade may manually enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.” RHSA-2025:23064
  • Red Hat Quay 3.12 quay 3.12-1765361593
    fixed: vendor fix “Users unable to upgrade may manually enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.” RHSA-2025:23028
  • Red Hat Quay 3.13 quay v3.13.10-1765782391
    fixed: vendor fix “Users unable to upgrade may manually enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.” RHSA-2025:23176
  • Red Hat Quay 3.14 quay 1773097621
    fixed: vendor fix “Users unable to upgrade may manually enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.” RHSA-2026:4215
  • Red Hat Quay 3.9 quay 3.9-1764254756, quay 3.14-1764254756, quay 3.14-1765382758, quay 8.10-1764254756, quay 8.10-1765382758, quay 3.9.17-1764254756, +2 more Red Hat Quay 3.10 quay 3.14-1764168428, quay 3.14-1765384144, quay 8.10-1764168428, quay 3.10.17-1764168428, quay 3.10.17-1765384144, quay v3.10.16-1764168428, +1 more Red Hat Quay 3.12 quay 3.14-1765361593, quay 8.10-1765361593, quay 3.12.13-1765361593, quay v3.12.0-1765361593 Red Hat Quay 3.13 quay v3.13.10-1765782391 Red Hat Quay 3.14 quay 1771008628, quay 1771265622, quay 1773097298, quay 1773097302, quay 1773097311, quay 1773097327, +3 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
12 mo ago

Exploit prediction

0.64% chance of exploitation in the next 30 days, higher than 50% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/authlib/authlib/security/advisories/GHSA-pq5p-34cr-23v9 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi authlib
<1.6.5
1.6.5

Affected products

  • authlib authlib

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.