PYSEC-2026-2294

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 rejectbytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different...

CVE-2026-54911

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 rejectbytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different...

CVE-2026-54911

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 rejectbytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different...

EUVD-2026-38362

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 rejectbytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different...

UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()

Summary ujson.dumps or ujson.dump or ujson.encode have a rejectbytes=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...