CVE-2026-32874
UltraJSON has a Memory Leak parsing large integers allows DoS
Impact
#### Summary ujson 5.4.0 to 5.11.0 inclusive contain an accumulating memory leak in JSON parsing _large_ (outside of the range [-2^63, 2^64 - 1]) integers. #### Exploitability Any service that calls `ujson.load()`/`ujson.loads()`/`ujson.decode()` on untrusted inputs is affected and vulnerable to denial of service attacks. #### Details 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. ```python ujson.loads(str(2 ** 64 - 1)) # No leak ujson.loads(str(2 ** 64)) # Leaks ujson.loads(str(10 ** sys.get_int_max_str_digits())) # Leaks and raises ValueError ``` #### Fix The leak is fixed in `ujson 5.12.0` (4baeb950df780092bd3c89fc702a868e99a3a1d2). There are no workarounds beyond upgrading to an unaffected version. #### Credits Discovered by Cameron Criswell/Skevros using Coverage-guided fuzzing (libFuzzer + AddressSanitizer)
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | ujson | >= 5.4.0, <= 5.11.0 | 5.12.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Ultrajson Project | Ultrajson | from 5.4.0 before 5.12.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- 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
- https://github.com/advisories/GHSA-wgvc-ghv9-3pmm
- https://nvd.nist.gov/vuln/detail/CVE-2026-32874