Security Bulletin:UltraJSON Malformed UTF-8 Byte Sequence Vulnerability

Summary 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...

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: Improper Input Validation

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-2026-32875

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.10 through 5.11.0 are vulnerable to buffer overflow or infinite loop through large indent handling. ujson.dumps crashes the Python interpreter segmentation fault when the product of the indent...

CVE-2026-32875: Integer Overflow or Wraparound

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.10 through 5.11.0 are vulnerable to buffer overflow or infinite loop through large indent handling. ujson.dumps crashes the Python interpreter segmentation fault when the product of the indent...