How severe is CVE-2025-61920?

CVE-2025-61920 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2025-61920 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-61920?

CVE-2025-61920 affects Authlib. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-61920?

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

Does CVE-2025-61920 have an EU (EUVD) identifier?

Yes. CVE-2025-61920 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-33768.

When was CVE-2025-61920 published?

CVE-2025-61920 was published on 2025-10-10 and last updated on 2026-06-17.

CVE-2025-61920

CVE-2025-61920 is a high-severity vulnerability in Authlib with a CVSS 3.x base score of 7.5. 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-20.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (44th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-33768
Weakness: CWE-20
Affected product: Authlib
Published: 2025-10-10
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-61920?: 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.
How severe is CVE-2025-61920?: CVE-2025-61920 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2025-61920 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (44th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-61920?: CVE-2025-61920 affects Authlib. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-61920?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-61920 have an EU (EUVD) identifier?: Yes. CVE-2025-61920 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-33768.
When was CVE-2025-61920 published?: CVE-2025-61920 was published on 2025-10-10 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:*

More vulnerabilities in Authlib

CVE-2026-28802 — Critical (CVSS 9.8): Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7,…
CVE-2026-27962 — Critical (CVSS 9.1): Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header…
CVE-2026-28498 — High (CVSS 7.5): Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level…
CVE-2025-59420 — High (CVSS 7.5): Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.4, Authlib’s JWS…
CVE-2024-37568 — High (CVSS 7.5): lepture Authlib before 1.3.1 has algorithm confusion with asymmetric public keys. Unless an algorithm is specified in a…
CVE-2026-28490 — Medium (CVSS 6.5): Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a cryptographic…

All CVEs affecting Authlib →

Other CWE-20 (Improper Input Validation) vulnerabilities

CVE-2026-48316 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48281 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48277 — Critical (CVSS 10.0): ColdFusion versions 2025.9, 2023.20 and earlier are affected by an Improper Input Validation vulnerability that could…
CVE-2026-48055 — Critical (CVSS 10.0): Streambert is a cross-platform Electron Desktop App to stream and download any video media. In versions 2.4.0 and…
CVE-2026-34910 — Critical (CVSS 10.0): A malicious actor with access to the network could exploit an Improper Input Validation vulnerability found in UniFi OS…
CVE-2026-33587 — Critical (CVSS 10.0): Lack of user input sanitisation in Open Notebook v1.8.3 allows the application user to execute Python code (and…

Browse all CWE-20 (Improper Input Validation) vulnerabilities →