CVE-2026-54911
Published:June 22, 2026
Updated:June 29, 2026
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.
Affected Packages
ujson (CONDA):
Affected version(s) >=1.33 <5.13.0Fix Suggestion:
Update to version 5.13.0https://github.com/ultrajson/ultrajson.git (GITHUB):
Affected version(s) >=2.0.0 <5.13.0Fix Suggestion:
Update to version 5.13.0ujson (PYTHON):
Affected version(s) >=1.4 <5.13.0Fix Suggestion:
Update to version 5.13.0Related Resources (4)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.9
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
LOW
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
6.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
Improper Input Validation
EPSS
Base Score:
0.27