Vulnerability Description
UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. This vulnerability is fixed in 5.13.0.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Ultrajson Project | Ultrajson | < 5.13.0 |
Related Weaknesses (CWE)
References
- https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6Patch
- https://github.com/ultrajson/ultrajson/releases/tag/5.13.0ProductRelease Notes
- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2MitigationPatchVendor Advisory
FAQ
What is CVE-2026-54911?
CVE-2026-54911 is a vulnerability with a CVSS score of 6.5 (MEDIUM). UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When ...
How severe is CVE-2026-54911?
CVE-2026-54911 has been rated MEDIUM with a CVSS base score of 6.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-54911?
Check the references section above for vendor advisories and patch information. Affected products include: Ultrajson Project Ultrajson.