CVE & CISA-KEV Catalog

CVE-2026-54911

MEDIUM
6.5
CVSS v3
NVD

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.

CWE-20Improper Input Validation

How to fix

Remediation Available
ultrajsonNVD
Affected:< 5.13.0Fixed in:5.13.0CVE-2026-54911derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork
Attack ComplexityLow
Privileges RequiredNone
User InteractionNone
ScopeUnchanged

Impact

ConfidentialityLow
IntegrityLow
AvailabilityNone

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

Exploit Intelligence

0.27%probability of exploitation in 30 days
19thpercentile

Low risk: more likely to be exploited than 19% of all known CVEs.

References

Release Notes1

Related Vulnerabilities

Other CWE-20 (Improper Input Validation) vulnerabilities, ordered by exploit likelihood. View all

CVESeverityCVSSEPSSExploitedFix
CVE-2024-3400Critical10.0100%KEV + Ransom-
CVE-2021-45105Medium5.9100%-Fix
CVE-2021-44228Critical10.0100%KEV + RansomFix
CVE-2021-21985Critical9.8100%KEV + RansomFix
CVE-2018-7600Critical9.8100%KEV + RansomFix
CVE-2020-3452High7.5100%KEVFix
Embed a live status badge for CVE-2026-54911
CVE-2026-54911 severity badge

Markdown

[![CVE-2026-54911](https://tridentstack.com/cve/badge/CVE-2026-54911.svg)](https://tridentstack.com/cve/CVE-2026-54911)

HTML

<a href="https://tridentstack.com/cve/CVE-2026-54911"><img src="https://tridentstack.com/cve/badge/CVE-2026-54911.svg" alt="CVE-2026-54911"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-26.