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No exploitation reportedFix available

CVE-2026-54911

No exploitation reported by the sources we read.

  • Published2026-06-22
  • Fixed in5.13.0
  • WeaknessCWE-20

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 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. This vulnerability is fixed in 5.13.0.

Timeline

dates in UTC
  1. 2026-06-2222:16CVE publishedNVD

Versions per branch

NVD · OSV
Ultrajson project ultrajson
BranchAffectedFixed in
5.13< 5.13.05.13.0

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
    • = < 5.13.0no fix stated

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-06-22

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

  • datahub-ingestionChainguardall versions · fixed in 1.6.0-r4
  • label-studioMinimOSall versions · fixed in 1.23.1-r0
  • openstack-glance-2025.1Chainguardall versions · fixed in 30.2.0_git20260616-r5
  • openstack-glance-2025.1-fipsChainguardall versions · fixed in 30.2.0_git20260617-r2
  • openstack-glance-2025.2Chainguardall versions · fixed in 31.1.0_git20260617-r4
  • openstack-glance-2025.2-fipsChainguardall versions · fixed in 31.1.0_git20260617-r3
  • openstack-glance-2026.1Chainguardall versions · fixed in 32.0.0_git20260625-r1
  • openstack-glance-2026.1-fipsChainguardall versions · fixed in 32.0.0_git20260617-r4

41 more package ranges on OSV.dev

Full record on NVD

Fix

  1. Update Ultrajson project ultrajson to 5.13.0

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

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionnone2026-06-23
  • CNACVSS 3.16.5known since 2026-10-23
  • CNAweakness (CWE)CWE-20known since 2026-10-23
  • FIRST EPSSEPSS score0.4 %2026-11-08
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryMODERATE2026-06-19

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Published
2026-06-22
Last Modified
2026-06-26
NVD status
Analyzed
GitHub Advisory
GHSA-3j69-69wj-xqx2

Frequently asked questions

What is CVE-2026-54911?

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. This vulnerability is fixed in 5.13.0.

Is CVE-2026-54911 actively exploited?

Active exploitation of CVE-2026-54911 has not been confirmed. Its EPSS score was 0.4% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-54911?

CVE-2026-54911 has a CVSS v3 base score of 6.5 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

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