UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-c38f-wx89-p2xg UltraJSON has a Memory Leak in ujson.dump() on Write Failure
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Tue, 02 Jun 2026 18:15:00 +0000

Type Values Removed Values Added
First Time appeared Ultrajson Project
Ultrajson Project ultrajson
CPEs cpe:2.3:a:ultrajson_project:ultrajson:*:*:*:*:*:python:*:*
Vendors & Products Ultrajson Project
Ultrajson Project ultrajson
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Sat, 30 May 2026 02:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 28 May 2026 02:15:00 +0000

Type Values Removed Values Added
First Time appeared Ultrajson
Ultrajson ultrajson
Vendors & Products Ultrajson
Ultrajson ultrajson

Wed, 27 May 2026 21:00:00 +0000

Type Values Removed Values Added
Description UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.
Title UltraJSON: Memory Leak in ujson.dump() on Write Failure
Weaknesses CWE-401
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-05-30T01:49:35.278Z

Reserved: 2026-05-07T16:20:08.659Z

Link: CVE-2026-44660

cve-icon Vulnrichment

Updated: 2026-05-30T01:49:25.859Z

cve-icon NVD

Status : Analyzed

Published: 2026-05-27T21:16:17.650

Modified: 2026-06-02T18:00:03.403

Link: CVE-2026-44660

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-28T02:00:04Z

Weaknesses