CVE-2026-5751

MEDIUMPre-NVD 6.16.1—
EchelonGraph scoreHIGH confidence

Score 6.1 from GitHub Security Advisory published 2026-08-23. a secondary CVSS source baseline 6.1; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
6.1EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.1Exploit: None knownExposed: 0

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

justhtml versions 1.13.0 and earlier contain a parser-differential / mutation cross-site scripting (mXSS) vulnerability when using a custom SanitizationPolicy that preserves foreign namespaces (e.g., drop_foreign_namespaces=False with allowlisted SVG/MathML elements or raw-text containers such as ). Specially crafted input can sanitize into markup that appears safe but becomes unsafe when re-parsed by a browser or another HTML parser, allowing markup injection. The default safe configuration (sanitize=True) is not affected. Fixed in 1.14.0.

CVSS v3
6.1
EG Score
6.1(high)
EG Risk
28(Track)
EG Risk 28/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity61% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
8%
KEV
Not listed

Published

August 23, 2026

Last Modified

August 26, 2026

Advisory Details (2)

Auto-updated Aug 23, 2026
Patch available. Sources: github.
generic

justhtml before 1.14.0 Mutation XSS via custom sanitization policies | Advisories | VulnCheck

https://www.vulncheck.com/advisories/justhtml-before-mutation-xss-via-custom-sanitization-policies
github Patch Available

Mutation XSS with custom foreign-namespace sanitization policies · Advisory · EmilStenstrom/justhtml · GitHub

https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-r758-8hxw-4845

Vendor Advisories for CVE-2026-5751(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
justhtml1.13.01.14.0—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 15× in last 7d / 15× 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. 2026-08-26 17:25 UTCEG score recompute
  2. 2026-08-26 17:25 UTCGHSA enrichment
  3. 2026-08-26 14:46 UTCEPSS rescore
  4. 2026-08-25 19:25 UTCEG score recompute
  5. 2026-08-25 19:25 UTCGHSA enrichment
  6. 2026-08-25 13:49 UTCEPSS rescore
  7. 2026-08-24 19:25 UTCEG score recompute
  8. 2026-08-24 19:25 UTCGHSA enrichment
  9. 2026-08-24 19:07 UTCEG score recompute
  10. 2026-08-24 19:07 UTCGHSA enrichment
  11. 2026-08-24 14:20 UTCEG score recompute
  12. 2026-08-24 14:20 UTCGHSA enrichment
  13. 2026-08-23 14:20 UTCEG score recompute
  14. 2026-08-23 13:51 UTCEG score recompute
  15. 2026-08-23 13:50 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-5751?
CVE-2026-5751 is a medium vulnerability published on August 23, 2026. justhtml versions 1.13.0 and earlier contain a parser-differential / mutation cross-site scripting (mXSS) vulnerability when using a custom SanitizationPolicy that preserves foreign namespaces (e.g., dropforeignnamespaces=False with allowlisted SVG/MathML elements or raw-text containers such as…
When was CVE-2026-5751 disclosed?
CVE-2026-5751 was first published in the National Vulnerability Database on August 23, 2026, with the most recent update on August 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-5751 actively exploited?
CVE-2026-5751 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 91.6% of all scored CVEs.
What is the CVSS score of CVE-2026-5751?
CVE-2026-5751 has a CVSS v3 base score of 6.1 (NVD).
How do I remediate CVE-2026-5751?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-5751, 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-2026-5751

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