6.5

CVE-2026-54911: ultrajson_project ultrajson Improper Input Validation

CVSS: 6.5v3.1MediumAnalyzed
AliasesGHSA-3j69-69wj-xqx2PYSEC-2026-2294UBUNTU-CVE-2026-54911
Published 22-06-2026Last modified 23-06-2026
Open JSON

Vulnerability summary

CVE-2026-54911 is a medium (CVSS 6.5) Improper Input Validation vulnerability in ultrajson_project ultrajson. EPSS estimates a 0.37% chance of exploitation in the next 30 days, higher than 29.6% of scored vulnerabilities.

Overall risk
26/100
0100
Medium · default modelHow is this calculated?
CVSS score
6.5/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.37%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 0 · Related 1
CGA-F367-HJWV-Q5GJ

Timeline

  1. 22-06-2026
    PublishedVulnerability first disclosed.
  2. 23-06-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

6 scores · 6 sources · 1 version

EPSS trend

Probability

0.37%

Chance of exploitation in the next 30 days

Percentile

30%

Versus all other CVEs

30-day change

0.00 pp

From 0.37% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.37%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard25 products
  • datahub-ingestion< 1.6.0-r4
  • openstack-glance-2025.1< 30.2.0_git20260616-r5
  • openstack-glance-2025.1-fips< 30.2.0_git20260617-r2
  • openstack-glance-2025.2< 31.1.0_git20260617-r4
  • openstack-glance-2025.2-fips< 31.1.0_git20260617-r3
Ubuntu3 products
  • collada2gltfAll versions (No fix recorded)
  • pandasAll versions (No fix recorded)
  • ujsonAll versions (No fix recorded)
Debian1 product
  • ujsonAll versions (No fix recorded) | < 5.13.0-1
PyPI1 product
  • ujson< 5.13.0
Ultrajson1 product
Ultrajson_project1 product

6 vendors · 32 products

References

10 links