CVE-2025-61920 | Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

Exp

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.

Published: 2025-10-10 Last update: 2025-11-03 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-61920 is rated High Exploit Risk (66.5/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.41%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2025-61920

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2025-61920

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-22 0.50% 0.41% -0.08%
2 2026-03-27 0.41% 0.50% +0.08%
3 2026-03-20 — 0.41% —

Full EPSS history (9 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-61920

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2025-61920

GitHub Security Advisory for CVE-2025-61920

GHSA-pq5p-34cr-23v9 · Severity: high · Ecosystem: pip — Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

OS Trackers for CVE-2025-61920

vendor priority summary link
debian not yet assigned CVE-2025-61920 not yet assigned priority: Debian including 1 source packages (python-authlib), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2025-61920
redhat high — https://access.redhat.com/security/cve/CVE-2025-61920
suse high — https://www.suse.com/security/cve/CVE-2025-61920/
ubuntu medium CVE-2025-61920 medium priority: Ubuntu including 1 source packages (python-authlib), 5 status rows across 5 suites (jammy, noble, plucky, questing, upstream): released 3, ignored 1, needed 1. https://ubuntu.com/security/CVE-2025-61920

Affected software / configurations for CVE-2025-61920

Vendor Product Version Raw CPE
authlib authlib < 1.6.5 cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:*

References for CVE-2025-61920

cvelogic Threat Intelligence