CVE-2026-44660: ultrajson — Exploit & Fix

Description

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0037

Probability of exploitation

0.29%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-401 CWE-401

Affected Products

Vendor	Product	Versions
ultrajson_project	ultrajson	< 5.12.1

References

Advisories & Patches

https://github.com/ultrajson/ultrajson/commit/82af1d0ac01d09aa40c887b460d44b9d9f4bccd9 https://github.com/ultrajson/ultrajson/security/advisories/GHSA-c38f-wx89-p2xg https://github.com/ultrajson/ultrajson/security/advisories/GHSA-c38f-wx89-p2xg

Exploits

https://github.com/ultrajson/ultrajson/security/advisories/GHSA-c38f-wx89-p2xg https://github.com/ultrajson/ultrajson/security/advisories/GHSA-c38f-wx89-p2xg

Other References

https://github.com/ultrajson/ultrajson/releases/tag/5.12.1

Frequently Asked Questions

What is CVE-2026-44660? +

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-44660? +

CVE-2026-44660 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0037, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-44660? +

CVE-2026-44660 affects products from ultrajson_project, specifically: ultrajson. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-44660? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-44660