Input validation error in ultrajson - CVE-2026-54911
Published: June 17, 2026
Vulnerability identifier: #VU134738
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-54911
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: ultrajson
Affected software:
ultrajson
ultrajson
Detailed vulnerability description
The vulnerability allows a remote attacker to bypass input validation and alter serialized data integrity.
The vulnerability exists due to improper input validation in ujson.dumps(), ujson.dump(), and ujson.encode() when processing malformed or truncated UTF-8 byte sequences with reject_bytes=False. A remote attacker can supply crafted byte sequences to bypass input validation and alter serialized data integrity.
The issue occurs only when the reject_bytes=False option is used.
How to mitigate CVE-2026-54911
Install security update from vendor's website.