Input validation error in ultrajson - CVE-2026-54911

Vulnerability identifier: #VU134738

CSH Severity: Medium

CVSS v4: 6.9 [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]

CVE-ID: CVE-2026-54911

CWE-ID: CWE-20

Exploitation vector: Remote access

Exploit availability: No public exploit available

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.

ultrajson
openEuler
python-ujson
python-ujson-debuginfo
python-ujson-debugsource
python-ujson-help
python3-ujson

Install security update from vendor's website.

ultrajson - update to 5.13.0
python-ujson - addressed in versions 4.0.2-3, 5.1.0-6, 5.1.0-7
python-ujson-debuginfo - addressed in versions 4.0.2-3, 5.1.0-6, 5.1.0-7
python-ujson-debugsource - addressed in versions 4.0.2-3, 5.1.0-6, 5.1.0-7
python-ujson-help - addressed in versions 4.0.2-3, 5.1.0-6, 5.1.0-7
python3-ujson - addressed in versions 4.0.2-3, 5.1.0-6, 5.1.0-7

• https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2
• https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf

• Input validation error in ultrajson
• openEuler 24.03 LTS SP3 update for python-ujson
• openEuler 24.03 LTS SP1 update for python-ujson
• openEuler 20.03 LTS SP4 update for python-ujson