joserfc has Possible Uncontrolled Resource Consumption Vulnerability Triggered by Logging Arbitrarily Large JWT Token
Affects joserfcSource GCVE Database
Not known to be exploited · CVSS 9.2 Critical : upgrade to 1.3.5 as a priority.
Data as of 27 Oct 2026, 18:28 UTC
- Patch
- Available – fixed in 1.3.5, 1.4.2
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:HExploitation evidence
Disclosed: evidence found.
CVE published 18 Nov 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade joserfc to 1.3.5; joserfc to 1.4.2.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| PyPIjoserfc | Affected
| Fixed in
|
| PyPIjoserfc | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A fix is available in joserfc versions 1.3.5 and 1.4.2. Users should upgrade to these or later versions to remediate the vulnerability. Additionally, it is critical to deploy Python web applications behind production-grade web servers or reverse proxies (e.g., uvicorn with appropriate settings, gunicorn, nginx) that enforce strict HTTP header size limits to prevent large JWT tokens from reaching the application. Without such infrastructure, the application remains vulnerable regardless of joserfc version.
Description
The joserfc library versions 1.3.3 up to but not including 1.3.5 and 1.4.0 up to but not including 1.4.2 contain a vulnerability where logging or diagnostic tools may process arbitrarily large JWT tokens embedded in exception messages. This can lead to uncontrolled resource consumption when a maliciously crafted large JWT token is sent to a Python web application that does not have proper HTTP header size limits enforced by its web server or reverse proxy.
References
- github.com/authlib/joserfc/security/advisories/GHSA-frfh-8v73-gjg4 (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2025-65015 (opens in a new tab)
- github.com/authlib/joserfc/commit/63932f169d924caffafa761af2122b82059017f7 (opens in a new tab)
- github.com/authlib/joserfc/commit/673c8743fd0605b0e1de6452be6cba75f44e466b (opens in a new tab)
- github.com/authlib/joserfc (opens in a new tab)
- github.com/authlib/joserfc/releases/tag/1.3.5 (opens in a new tab)
- github.com/authlib/joserfc/releases/tag/1.4.2 (opens in a new tab)
- github.com/pypa/advisory-database/tree/main/vulns/joserfc/PYSEC-2026-361.yaml (opens in a new tab)
- pypi.org/project/joserfc (opens in a new tab)