Описание
UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()
Summary
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.
Details
The expected behavior is that for x being any bytes string, x == ujson.loads(ujson.dumps(x, reject_bytes=False)).encode(errors="surrogatepass") should always either be true or ujson.dumps() will throw an exception. In reality, some strings which should've been errors are silently rewritten as other strings:
- Invalid continuation bytes are replaced with valid ones:
b'\xcf\x13'->b'\xcf\x93' - Unterminated sequence completes the sequence:
b'\xc3'->b'\xc3\x80' - ... or leads to reading past the end of string:
b'\xf0\x90\x94'->b"\xf0\x90\x94\x80inxcontrib'"
Impact
An application relying on reject_bytes=False for UTF-8 handling may experience:
- Data integrity issues
- Experience validation bypass if said validation occurs before serialisation
Remediation
The missing/broken UTF-8 validation checks were added/fixed in https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf. We recommend upgrading to UltraJSON 5.13.0.
Workarounds
Decoding bytes to strings in Python before passing them to ujson.dumps() avoids this issue.
Ссылки
- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2
- https://nvd.nist.gov/vuln/detail/CVE-2026-54911
- https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf
- https://github.com/pypa/advisory-database/tree/main/vulns/ujson/PYSEC-2026-2294.yaml
- https://github.com/ultrajson/ultrajson/releases/tag/5.13.0
Пакеты
ujson
<= 5.12.1
5.13.0
Связанные уязвимости
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.
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.
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.
UltraJSON is a fast JSON encoder and decoder written in pure C with bi ...