CVE-2026-32874 UltraJSON has a Memory Leak parsing large integers allows DoS
Attackers can cause denial of service by sending JSON with large integers, leading to memory leaks in the UltraJSON library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-32874?
CVE-2026-32874 is a high-severity denial of service vulnerability in ultrajson, published on 20 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-32874?
3 open source packages ship an affected version, including ujson. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
ujson PyPI | From 5.4.0 | 5.12.0 |
ujson PyPI | From 5.4.0 | 5.12.0 |
ujson PyPI | From 5.4.0 | 5.12.0 |
Products include Ultrajson Project Ultrajson.
How do I fix CVE-2026-32874?
Upgrade ujson to 5.12.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-32874 being exploited?
There is no known exploitation of CVE-2026-32874 in the wild and no public exploit code.
Other vulnerabilities in ultrajson
Sources
Also known as DEBIAN-CVE-2026-32874, ECHO-1418-3756-d634, GHSA-wgvc-ghv9-3pmm, MINI-mq5m-2pgm-4wpx, PYSEC-2026-2291, ROOT-APP-PYPI-CVE-2026-32874 and 1 more.