CVE-2025-65015: 
Python vulnerability analysis and mitigation

CVE-2025-65015 affects joserfc, a Python library that implements JSON Object Signing and Encryption (JOSE) standards. The vulnerability was discovered in versions >=1.3.3 and <= 1.4.1, with patches released in versions 1.3.5 and 1.4.2. The issue involves the ExceededSizeError exception messages containing non-decoded JWT token parts that could potentially cause Python logging to record arbitrarily large, forged JWT payloads (GitHub Advisory).

The vulnerability is classified as an Allocation of Resources Without Limits or Throttling (CWE-770) issue. When processing JWT tokens, the library embeds the full payload in exception messages during validation of header, payload, and signature sizes. This occurs in multiple validation methods within the codebase, specifically in joserfc/rfc7515/registry.py and joserfc/rfc7516/registry.py. The CVSS v4.0 score is 9.2 (Critical), with the vector string CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H (GitHub Advisory).

In scenarios where a web application does not reject excessively large HTTP header payloads, the vulnerability can lead to system resource exhaustion affecting disk, memory, and CPU on the application host. Additionally, it may impact external log storage, ingestion pipelines, and alerting services. The issue becomes particularly concerning when the application runs without proper web server configurations that would normally limit header sizes (GitHub Advisory).

The issue has been patched in joserfc versions 1.3.5 and 1.4.2. Users should upgrade to these patched versions. Additionally, it is recommended to deploy the library behind a robust web server or reverse proxy that correctly enforces maximum request header sizes. For example, using nginx can explicitly cap maximum header size (GitHub Advisory).