TI-2026-05042 Aliases CVE-2026-5751 GHSA-3227-3f97-9f2q

justhtml before 1.14.0 Mutation XSS via custom sanitization policies

LOW 23CWE-79Published 2026-08-23 · Updated 2026-08-24

Key facts

Attack vector: Network
Privileges required: None
User interaction: Active
Attack complexity: Low
Attack requirements: None
Impact type: Cross-site scripting
Confidentiality · integrity · availability: None · None · None
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

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 <style>). 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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00263 18th percentileScored 2026-11-07

Fix Fixed justhtml (EmilStenstrom): 1.14.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
EmilStenstrom	justhtml	before 1.14.0	1.14.0	Patch available	CNA

justhtml VendorEmilStenstrom Affected before 1.14.0 Fixed in 1.14.0 Patch available CNA

Remediation

Fix · CNA justhtml (EmilStenstrom) Fixed in 1.14.0

Timeline

2026-10-02 Threatist record created from CVE-2026-5751
2026-10-03 Alias added: GHSA-3227-3f97-9f2q

References

Advisory 1

GitHub Security Advisory (GHSA-r758-8hxw-4845)

TI-2026-07422 justhtml before 1.12.0 Sanitizer Bypass via Markdown CVSS 4.0CRITICAL 9.3
TI-2026-08560 justhtml before 1.10.0 Denial of Service via deeply nested HTML CVSS 4.0HIGH 8.7
TI-2026-52557 justhtml before 3.11.0 XSS via selectedcontent projection CVSS 4.0MEDIUM 5.1
TI-2026-04717 justhtml before 1.13.0 XSS via code fence breakout CVSS 4.0MEDIUM 5.1
TI-2026-06871 justhtml before 1.16.0 Multiple Security Issues via Sanitization CVSS 4.0CRITICAL 9.3
TI-2026-04716 justhtml before 1.15.0 Multiple Security Issues CVSS 4.0CRITICAL 9.3

See all 10 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences