UltraJSON has a Memory Leak parsing large integers allows DoS

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-32874: 0.50% estimated exploitation activity in the next 30 days; percentile 42.69 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.getintmaxstrdigits() 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. 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)

Published by the source

18 Mar 2026, 13:01 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:37 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wgvc-ghv9-3pmm

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wgvc-ghv9-3pmm

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# Patch Next advisory brief: CVE-2026-32874

Advisory: UltraJSON has a Memory Leak parsing large integers allows DoS
IDs: CVE-2026-32874, GHSA-wgvc-ghv9-3pmm
Record: https://patchnext.com/advisories/cve-2026-32874 (revision 2, source checked 26 Oct 2026, 13:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ujson 5.12.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI ujson: affected >= 5.4.0, <= 5.11.0; fixed in 5.12.0

## Suggested inspection (read-only)
- `python -m pip show ujson`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ujson.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wgvc-ghv9-3pmm (OSV record GHSA-wgvc-ghv9-3pmm lists affected ranges: PyPI ujson >=5.4.0 <5.12.0 (fixed))
- Verified: https://github.com/advisories/GHSA-wgvc-ghv9-3pmm (GitHub-reviewed advisory GHSA-wgvc-ghv9-3pmm lists affected ranges: PyPI ujson >=5.4.0 <=5.11.0)

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