# CVE-2026-32874: ujson: UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+

CVE-2026-32874 is fixed in 2 products on 1 platform, first by python3-ujson 5.9.0-1ubuntu0.1~esm1, released March 19, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-32874
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0051
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 19, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | python3-ujson Ubuntu 24.04.5 LTS (noble) | 5.9.0-1ubuntu0.1~esm1 | [python3-ujson 5.9.0-1ubuntu0.1~esm1](https://patchblox.com/security/data/fix/linux/ubuntu-noble-python3-ujson-5.9.0-1ubuntu0.1-esm1.md) | Mar 19, 2026 |
| Linux | python3-ujson Ubuntu 25.10 (questing) | 5.10.0-1ubuntu0.1 | [python3-ujson 5.10.0-1ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-questing-python3-ujson-5.10.0-1ubuntu0.1.md) | Mar 19, 2026 |
| Linux | python3-ujson Ubuntu 26.04.1 LTS (resolute) | 5.11.0-3ubuntu0.1 | [python3-ujson 5.11.0-3ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-python3-ujson-5.11.0-3ubuntu0.1.md) | Mar 19, 2026 |
| Linux | ujson Debian 14 | 5.13.0-1 | [DEBIAN-CVE-2026-32874](https://patchblox.com/security/data/fix/linux/debian-cve-2026-32874.md) | Mar 20, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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