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Not in CISA KEV
HIGH severity

UltraJSON has a Memory Leak parsing large integers allows DoSGHSA-wgvc-ghv9-3pmm

HIGHFix: ultrajson/ultrajson@4baeb95

GHSA-wgvc-ghv9-3pmm is a high-severity (CVSS 7.5) CWE-401 vulnerability in ujson. A fix is available for ujson — see the affected versions and patch details below.

Also known asCVE-2026-32874PYSEC-2026-2291
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-wgvc-ghv9-3pmm.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs43th percentile — riskier than 43% of all scored CVEsHighest risk
0.00%0.39%0.79%1.18%0.1%0.5%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍ujson

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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.

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

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIujson≥ 5.4.0&&< 5.12.05.12.0pip install --upgrade 'ujson==5.12.0'

Affected Products

1 product · 1 configurations
Application
ultrajsonultrajson_project
≥ 5.4.0 && < 5.12.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ujson, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update ujson to 5.12.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-wgvc-ghv9-3pmm is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This IMPORTANT flaw in UltraJSON can lead to a denial of service in services that process untrusted JSON inputs. Specially crafted JSON containing excessively large integers can trigger a memory leak, consuming system resources. This affects Red Hat OpenStack Platform and Community Projects utilizing `python-ujson`.

Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Source: Red Hat security advisory for GHSA-wgvc-ghv9-3pmm (CC BY 4.0)

Frequently Asked Questions

#### 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
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