Vulnerability · Published Mar 20, 2026 · Assigned by GitHub_M
CVE-2026-32874UltraJSON has a Memory Leak parsing large integers allows DoS
High 7.5
In plain English
A high-severity memory leak in ultrajson from ultrajson. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 44% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | py3-ujson | 5.12.0-r0 | ALPINE-CVE-2026-32874 |
| Alpine:v3.24 | py3-ujson | 5.12.0-r0 | ALPINE-CVE-2026-32874 |
| Debian:12 | ujson | no fix listed | DEBIAN-CVE-2026-32874 |
| Debian:13 | ujson | no fix listed | DEBIAN-CVE-2026-32874 |
| Debian:14 | ujson | 5.13.0-1 | DEBIAN-CVE-2026-32874 |
| PyPI | ujson | 5.12.0 | PYSEC-2026-2291 |
| PyPI | ujson | 5.12.0 | GHSA-wgvc-ghv9-3pmm |
| Ubuntu:25.10 | ujson | 5.10.0-1ubuntu0.1 | UBUNTU-CVE-2026-32874 |
| Ubuntu:26.04:LTS | ujson | 5.11.0-3ubuntu0.1 | UBUNTU-CVE-2026-32874 |
| Ubuntu:26.10 | ujson | no fix listed | UBUNTU-CVE-2026-32874 |
Affected products (as reported)
Weakness: CWE-401, CWE-772 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-wgvc-ghv9-3pmm x_refsource_CONFIRM
- https://github.com/ultrajson/ultrajson/commit/4baeb950df780092bd3c89fc702a868e99a3a1d2 x_refsource_MISC
- https://github.com/ultrajson/ultrajson/releases/tag/5.12.0 x_refsource_MISC
- https://access.redhat.com/security/cve/CVE-2026-32874 vdb-entry, x_refsource_REDHAT
- RHBZ#2449411 issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-32874.json x_sadp-csaf-vex