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TI-2026-25334 Aliases CVE-2026-32874GHSA-wgvc-ghv9-3pmm

UltraJSON has a Memory Leak parsing large integers allows DoS

Priority LOW 39CWE-401Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-401.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00508 43rd percentileScored 2026-11-07
Fix Fixed ultrajson (ultrajson): 5.12.0ujson (PyPI): 5.12.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
ultrajsonultrajson5.4.0 to before 5.12.05.12.0Patch availableCNA
—ujson (PyPI)5.4.0 to before 5.12.05.12.0Patch availableGHSA-wgvc-ghv9-3pmm
  • ultrajson Vendorultrajson Affected 5.4.0 to before 5.12.0 Fixed in 5.12.0 Patch available CNA
  • ujson (PyPI) Vendor— Affected 5.4.0 to before 5.12.0 Fixed in 5.12.0 Patch available GHSA-wgvc-ghv9-3pmm

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:ultrajson_project:ultrajson:*:*:*:*:*:python:*:*5.4.0 to before 5.12.0Vulnerableultrajson
  • cpe:2.3:a:ultrajson_project:ultrajson:*:*:*:*:*:python:*:* Versions 5.4.0 to before 5.12.0 Vulnerable ·ultrajson

Remediation

  • Fix · CNA ultrajson (ultrajson) Fixed in 5.12.0
  • Fix · GHSA-wgvc-ghv9-3pmm ujson (PyPI) Fixed in 5.12.0 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

Not affected: 3 products
  • Red Hat OpenStack Platform 16.2
  • Red Hat OpenStack Platform 17.1
  • Red Hat OpenStack Platform 18.0

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-32874
  2. 2026-10-03 Alias added: GHSA-wgvc-ghv9-3pmm
  3. 2026-10-25 EPSS moved to the below the 50th percentile
  4. 2026-10-25 Priority changed: MEDIUM → LOW

References

Patch 1

Advisory 2

Other 2

  • TI-2026-32560 UltraJSON: Memory Leak in ujson.dump() on Write Failure CVSS 4.0HIGH 8.7
  • TI-2026-25335 UltraJSON has an integer overflow handling large indent leads to buffer overflow or infinite loop CVSS 3.1HIGH 7.5
  • TI-2022-13160 Incorrect handling of invalid surrogate pair characters in ujson CVSS 3.1HIGH 7.5
  • TI-2026-39683 UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps() CVSS 3.1MEDIUM 6.5
  • TI-2022-13161 Double free of buffer during string decoding in ujson CVSS 3.1MEDIUM 5.9
  • TI-2021-20961 UltraJSON (aka ujson) through 5.1.0 has a stack-based buffer overflow in… CVSS 3.1MEDIUM 5.5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences