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CVE-2025-61920

Authlib denial of service

7.5 HIGHPublic exploitEPSS 0.64%
  1. Published10 Oct 2025

Description

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Authlib< 1.6.5

Remediation

Fixed in
Authlib≥ 1.6.5

References

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Frequently asked

Is CVE-2025-61920 being actively exploited?

CVE-2025-61920 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.64%.

How severe is CVE-2025-61920?

CVE-2025-61920 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.64% probability of exploitation.

Which products are affected by CVE-2025-61920?

Affected products include Authlib.

How do I fix CVE-2025-61920?

Upgrade affected software to a fixed version, for example Authlib 1.6.5 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-61920 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.