CVE-2026-54911

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 81% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 6.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
6.5
EG Score
6.5(medium)
EPSS
19.0%
KEV
Not listed

Published

June 19, 2026

Last Modified

June 26, 2026

Advisory Details (3)

Auto-updated Jun 23, 2026
Patch available. Sources: github, github_commit, github_release.
github_release Patch Available

5.13.0

Patch available: ultrajson/ultrajson 5.13.0

https://github.com/ultrajson/ultrajson/releases/tag/5.13.0
github_commit Patch Available

commit 169eaf36b111 (ultrajson/ultrajson)

Patch available: ultrajson/ultrajson 5.13.0 (contains commit 169eaf36b111)

https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf
github Patch Available

Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps() · Advisory · ultrajson/ultrajson · GitHub

https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2

Vendor Advisories for CVE-2026-54911(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
ujson1.15 ... 5.9.0 (41 versions)5.13.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 16× in last 7d / 36× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-06 16:27 UTCEPSS rescore
  2. 2026-07-06 16:27 UTCEPSS rescore
  3. 2026-07-06 09:30 UTCEG score recompute
  4. 2026-07-06 02:23 UTCEPSS rescore
  5. 2026-07-06 02:23 UTCEPSS rescore
  6. 2026-07-05 06:46 UTCEG score recompute
  7. 2026-07-05 02:31 UTCEPSS rescore
  8. 2026-07-05 02:30 UTCEPSS rescore
  9. 2026-07-04 06:31 UTCEPSS rescore
  10. 2026-07-04 06:31 UTCEPSS rescore
  11. 2026-07-04 04:20 UTCEG score recompute
  12. 2026-07-03 01:17 UTCEG score recompute
  13. 2026-07-01 22:59 UTCEG score recompute
  14. 2026-07-01 15:07 UTCEPSS rescore
  15. 2026-06-30 23:22 UTCEPSS rescore
  16. 2026-06-30 20:42 UTCEG score recompute
  17. 2026-06-29 18:17 UTCEG score recompute
  18. 2026-06-29 14:06 UTCEPSS rescore
  19. 2026-06-29 14:06 UTCEPSS rescore
  20. 2026-06-28 15:50 UTCEG score recompute
  21. 2026-06-28 14:07 UTCEPSS rescore
  22. 2026-06-28 04:56 UTCEPSS rescore
  23. 2026-06-28 04:56 UTCEPSS rescore
  24. 2026-06-27 13:33 UTCEG score recompute
  25. 2026-06-27 03:08 UTCEPSS rescore
Show 11 more
  1. 2026-06-26 11:15 UTCEG score recompute
  2. 2026-06-25 13:49 UTCEPSS rescore
  3. 2026-06-25 08:57 UTCEG score recompute
  4. 2026-06-24 14:05 UTCEPSS rescore
  5. 2026-06-24 06:41 UTCEG score recompute
  6. 2026-06-23 21:33 UTCEPSS rescore
  7. 2026-06-23 21:33 UTCEPSS rescore
  8. 2026-06-23 04:22 UTCEG score recompute
  9. 2026-06-22 02:03 UTCEG score recompute
  10. 2026-06-20 23:44 UTCEG score recompute
  11. 2026-06-19 21:24 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-54911?
CVE-2026-54911 is a medium vulnerability published on June 19, 2026. 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…
When was CVE-2026-54911 disclosed?
CVE-2026-54911 was first published in the National Vulnerability Database on June 19, 2026, with the most recent update on June 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-54911 actively exploited?
CVE-2026-54911 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 19.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-54911?
CVE-2026-54911 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-54911?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-54911, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-54911

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