CVSS 3.1
6.5 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:NCVE-2026-54911
Medium (6.5) in ultrajson project ultrajson. EPSS 0.4% chance of exploitation in the next 30 days. Fixed in ujson 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.
Severity
- EPSS
- 0.4% chance of exploitation in the next 30 days; higher than 31% of CVEs (scores of 2026-10-31)
- CWE
- CWE-20
- Published
- Modified
- Record from
- the NVD, synced
Affected
- ultrajson_project:ultrajson
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-3j69-69wj-xqx2 | PyPI | ujson | <5.13.0 | 5.13.0 |
| PYSEC-2026-2294 | PyPI | ujson | <5.13.0 | 5.13.0 |