Quick answers
- Is CVE-2026-44660 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-44660 being exploited in the wild.
- How severe is CVE-2026-44660?
- High severity, with a CVSS score of 7.5, published 27 May 2026.
- Which products and versions are affected?
- ujson (PyPI) <= 5.12.0, ECOSYSTEM:introduced=0,fixed=5.12.1; UltraJSON < 5.12.1, <= 5.12.0.
- Is there a fix for CVE-2026-44660?
- Yes. ujson (PyPI): upgrade to 5.12.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-44660 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-44660?
- Check whether you run ujson (PyPI) or UltraJSON at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- ujson (PyPI): upgrade to 5.12.1 or later
pip install "ujson>=5.12.1"
Technical details
A memory leak exists in UltraJSON's `objToJSONFile()` function within `src/ujson/python/objToJSON.c`. The function allocates a Python string object for serialized JSON data but fails to call `Py_DECREF()` if the subsequent `write()` call on the file-like object raises an exception. This results in a leak of the full serialized payload size for every failed write. An attacker can trigger this by inducing write failures, such as closing a network connection mid-response on a server using `ujson.dump()`. The issue is fixed in version 5.12.1. Applications using `ujson.dumps()` are unaffected.
Affected products
- UltraJSON ujson <= 5.12.0
Identifiers
- CVE-2026-44660
- GHSA-c38f-wx89-p2xg
- PYSEC-2026-2293
Timeline
- 2026-05-07: disclosed: Initial disclosure on GitHub
- 2026-05-12: advisory: GitHub Advisory published
- 2026-05-27: other: NVD published date