UltraJSON up to 5.11.x on Python ujson.dumps integer overflow

Summaryinfo

A vulnerability was found in UltraJSON up to 5.11.x on Python. It has been classified as problematic. The affected element is the function ujson.dumps. The manipulation leads to integer overflow. This vulnerability is uniquely identified as CVE-2026-32875. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in UltraJSON up to 5.11.x on Python and classified as problematic. This issue affects the function ujson.dumps. The manipulation with an unknown input leads to a integer overflow vulnerability. Using CWE to declare the problem leads to CWE-190. The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. Impacted is availability. The summary by CVE is:

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Versions 5.10 through 5.11.0 are vulnerable to buffer overflow or infinite loop through large indent handling. ujson.dumps() crashes the Python interpreter (segmentation fault) when the product of the indent parameter and the nested depth of the input exceeds INT32_MAX. It can also get stuck in an infinite loop if the indent is a large negative number. Both are caused by an integer overflow/underflow whilst calculating how much memory to reserve for indentation. And both can be used to achieve denial of service. To be vulnerable, a service must call ujson.dump()/ujson.dumps()/ujson.encode() whilst giving untrusted users control over the indent parameter and not restrict that indentation to reasonably small non-negative values. A service may also be vulnerable to the infinite loop if it uses a fixed negative indent. An underflow always occurs for any negative indent when the input data is at least one level nested but, for small negative indents, the underflow is usually accidentally rectified by another overflow. This issue has been fixed in version 5.12.0.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-32875 since 03/16/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 303240 (Linux Distros Unpatched Vulnerability : CVE-2026-32875), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.12.0 eliminates this vulnerability. Applying the patch 486bd4553dc471a1de11613bc7347a6b318e37ea is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (303240). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Name

• UltraJSON

Version

• 5.0
• 5.1
• 5.2
• 5.3
• 5.4
• 5.5
• 5.6
• 5.7
• 5.8
• 5.9
• 5.10
• 5.11

License

• open-source

Website

• Product: https://github.com/ultrajson/ultrajson/

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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