CVE-2026-32874: ultrajson_project ultrajson

Vulnerability summary

CVE-2026-32874 is a high (CVSS 7.5) vulnerability in ultrajson_project ultrajson. EPSS estimates a 0.71% chance of exploitation in the next 30 days, higher than 52.6% of scored vulnerabilities.

Timeline

1. 20-03-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

Description

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.4.0 through 5.11.0 contain an accumulating memory leak in JSON parsing large (outside of the range [-2^63, 2^64 - 1]) integers. The leaked memory is a copy of the string form of the integer plus an additional NULL byte. The leak occurs irrespective of whether the integer parses successfully or is rejected due to having more than sys.get_int_max_str_digits() digits, meaning that any sized leak per malicious JSON can be achieved provided that there is no limit on the overall size of the payload. Any service that calls ujson.load()/ujson.loads()/ujson.decode() on untrusted inputs is affected and vulnerable to denial of service attacks. This issue has been fixed in version 5.12.0.

• CWE-401Missing Release of Memory after Effective LifetimeThe product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.
• CWE-772Missing Release of Resource after Effective LifetimeThe product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.