CVE-2026-32874
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.48%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.48% probability · 40th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-401, CWE-772
- Affected
- ultrajson project/ultrajson
- Source
- security-advisories@github.com
References
- https://github.com/ultrajson/ultrajson/commit/4baeb950df780092bd3c89fc702a868e99a3a1d2Patch
- https://github.com/ultrajson/ultrajson/releases/tag/5.12.0Product, Release Notes
- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-wgvc-ghv9-3pmmVendor Advisory
- https://access.redhat.com/security/cve/CVE-2026-32874
- https://bugzilla.redhat.com/show_bug.cgi?id=2449411
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-32874.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.