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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History
Mon, 22 Jun 2026 22:00:00 +0000
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| 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. | |
| Title | UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps() | |
| Weaknesses | CWE-20 | |
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cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-06-22T20:53:07.019Z
Reserved: 2026-06-16T13:49:33.556Z
Link: CVE-2026-54911
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
Updated: 2026-06-22T23:45:04Z