Bug 2491538 (CVE-2026-54911) - CVE-2026-54911 UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()
Summary: CVE-2026-54911 UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rew...
Keywords:
Status: NEW
Alias: CVE-2026-54911
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-06-22 22:01 UTC by OSIDB Bzimport
Modified: 2026-07-13 15:18 UTC (History)
23 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-06-22 22:01:28 UTC 
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.
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