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.
Weakness
The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Ultrajson | Ultrajson_project | 5.4.0 (including) | 5.12.0 (excluding) |
| Ujson | Ubuntu | devel | * |
| Ujson | Ubuntu | esm-apps/noble | * |
| Ujson | Ubuntu | esm-apps/resolute | * |
| Ujson | Ubuntu | noble | * |
| Ujson | Ubuntu | questing | * |
| Ujson | Ubuntu | resolute | * |
| Ujson | Ubuntu | upstream | * |
Potential Mitigations
- Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
- For example, glibc in Linux provides protection against free of invalid pointers.
- When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
- To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.
References
- https://github.com/ultrajson/ultrajson/commit/4baeb950df780092bd3c89fc702a868e99a3a1d2
- https://github.com/ultrajson/ultrajson/releases/tag/5.12.0
- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-wgvc-ghv9-3pmm
- https://access.redhat.com/security/cve/CVE-2026-32874
- https://bugzilla.redhat.com/show_bug.cgi?id=2449411
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-32874.json