VulnerabilityAnalyzed

CVE-2026-54911

This leads to input validation bypass and data integrity issues.

MEDIUM 6.5EPSS 0.37%

Does this matter?

Lower severity and a low EPSS score (0.37%). Track it; it rarely justifies an emergency change on its own.

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 3.1: 6.5 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
EPSS: 0.37% probability · 31th percentile
CISA KEV: Not listed
Weakness: CWE-20
Affected: ultrajson project/ultrajson
Source: security-advisories@github.com

References

https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcfPatch
https://github.com/ultrajson/ultrajson/releases/tag/5.13.0Product, Release Notes
https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2Mitigation, Patch, Vendor Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.