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Public proof of conceptFix available

CVE-2026-44660

A public proof of concept exists; no exploitation attested.

  • Published2026-05-27
  • Fixed in5.12.1
  • WeaknessCWE-401

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.

Timeline

dates in UTC
  1. 2026-05-2721:16CVE publishedNVD

Versions per branch

NVD · OSV
Ultrajson project ultrajson
BranchAffectedFixed in
5.12< 5.12.15.12.1

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As GitHub_M, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • ultrajson
    Affected
    • = < 5.12.1no fix stated

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-05-27

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • label-studioMinimOSall versions · fixed in 1.23.1-r0
  • label-studioChainguardall versions · fixed in 1.23.0-r5
  • pandasUbuntu:20.04:LTSall versions · no fixed version listed
  • pandasUbuntu:18.04:LTSall versions · no fixed version listedand 1 other package
  • pandasUbuntu:16.04:LTSall versions · no fixed version listedand 1 other package
  • pandasUbuntu:14.04:LTSall versions · no fixed version listed
  • python-ujsonSUSE:Linux Enterprise Server for SAP applications 16.0all versions · fixed in 5.10.0-160000.3.1
  • python-ujsonSUSE:Linux Enterprise Server for SAP Applications 15 SP6all versions · fixed in 1.35-150100.3.13.1

29 more package ranges on OSV.dev

Vendor advisories

  • CVE-2026-44660 Red Hat Product Security25 products fixed · 6 known affected

    python-ujson: UltraJSON: Memory leak leading to Denial of Service

    exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 as a component of Exploit Intelligence · rhelai3/bootc-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3 · rhelai3/bootc-gaudi-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3 · +3 more

  • RHSA-2026:87410 Red Hat Product Security3 products fixed

    Red Hat Security Advisory: RHOAI 2.25.12 - Red Hat OpenShift AI

  • RHSA-2026:84734 Red Hat Product Security3 products fixed

    Red Hat Security Advisory: RHOAI 3.4.5 - Red Hat OpenShift AI

  • RHSA-2026:60520 Red Hat Product Security13 products fixed

    Red Hat Security Advisory: RHOAI 3.4.4 - Red Hat OpenShift AI

  • RHSA-2026:51347 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: General availability of the satellite/iop-host-inventory-rhel9 container image

  • RHSA-2026:51195 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: General availability of the satellite/iop-host-inventory-rhel9 container image

1 more advisory

Full record on NVD

Fix

  1. Update Ultrajson project ultrajson to 5.12.1
  2. Vendor fix Red Hat Product Security RHSA-2026:87410 · 3 productsFor Red Hat OpenShift AI 2.25.12 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
  3. Vendor fix Red Hat Product Security RHSA-2026:84734 · 3 productsFor Red Hat OpenShift AI 3.4.5 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
  4. Vendor fix Red Hat Product Security RHSA-2026:60520 · 13 productsFor Red Hat OpenShift AI 3.4.4 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
  5. Vendor fix Red Hat Product Security RHSA-2026:51347 · 1 productFor Red Hat Lightspeed in Satellite installation see the Red Hat Satellite documentation.
  6. Vendor fix Red Hat Product Security RHSA-2026:42644 · 4 productsFor Red Hat OpenShift AI 2.25.9 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
  7. Workaround from the vendor Red Hat Product Security RHSA-2026:87410 · 205 productsMitigation 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.

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CISA-ADPSSVC decisionpoc2026-05-30
  • CNACVSS 4.08.7known since 2026-10-23
  • NVDCVSS 3.17.5read 2026-10-23
  • CNAweakness (CWE)CWE-401known since 2026-10-23
  • FIRST EPSSEPSS score0.4 %2026-11-08
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryHIGH2026-05-12

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2026-05-27
Last Modified
2026-06-17
NVD status
Analyzed
GitHub Advisory
GHSA-c38f-wx89-p2xg

Frequently asked questions

What is CVE-2026-44660?

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.

Is CVE-2026-44660 actively exploited?

A proof-of-concept exploit exists for CVE-2026-44660, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-44660?

CVE-2026-44660 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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