CVE-2026-6827
Received Received - Intake

justhtml Multiple Security Vulnerabilities Before 1.17.0

Publication date: 2026-08-23

Last updated on: 2026-08-23

Assigner: VulnCheck

Description
justhtml before 1.17.0 contains multiple security issues in sanitization, serialization, and programmatic DOM handling. When custom policies preserve foreign namespaces (SVG/MathML), dangerous content such as HTML integration points (SVG <foreignObject>, MathML <annotation-xml encoding="text/html">) and mutation-XSS parser-differential payloads could survive sanitization and become active HTML after reparse; SVG filter="url(...)" and preserved <style> could leave resource-loading CSS (@import, background-image:url()). Programmatic script/style/Comment nodes could serialize into active markup. Additional hardening fixes address sanitize-pipeline cache mutation and DOM parent/child cycles that could cause infinite loops. Most issues affect advanced or custom configurations rather than the default JustHTML(..., sanitize=True) safe path.

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Meta Information

Published
2026-08-23
Last Modified
2026-08-23
Generated
2026-08-23
AI Q&A
2026-08-23
EPSS Evaluated
N/A
NVD
CVE-2026-6827
EUVD
EUVD-2026-64655

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
justhtml justhtml to 1.17.0 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

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Executive Summary

CVE-2026-6827 affects justhtml versions before 1.17.0 with multiple XSS vulnerabilities due to improper sanitization, serialization, and DOM handling. When custom policies preserve foreign namespaces like SVG or MathML, dangerous content such as HTML integration points or mutation-XSS payloads can bypass sanitization and become active HTML after re-parsing. SVG filter attributes and preserved style tags may enable CSS-based attacks. Programmatic script/style/comment nodes could serialize into executable markup. Additional issues include cache mutation and DOM cycles causing infinite loops.

Detection Guidance

Check justhtml version with npm list justhtml or grep in package.json. Inspect custom sanitization policies for preserved SVG/MathML namespaces. Monitor for unusual DOM parsing behavior or infinite loops in sanitization pipelines.

Impact Analysis

This vulnerability allows attackers to execute malicious scripts in user browsers through XSS attacks. It can lead to data theft, session hijacking, or defacement of web pages. The impact is higher in advanced or custom configurations where foreign namespaces like SVG or MathML are preserved. Default safe configurations with sanitize=True are not affected.

Compliance Impact

This vulnerability primarily enables Cross-Site Scripting (XSS) attacks, which could lead to unauthorized data access or manipulation. For GDPR, this may violate principles of data protection by design and default (Article 25) if user data is compromised. HIPAA compliance could be impacted if protected health information is exposed or altered through XSS in healthcare applications.

Mitigation Strategies

Upgrade justhtml to version 1.17.0 or later. Avoid preserving SVG, MathML, or style tags for untrusted input. Disable programmatic DOM mutations with untrusted content. Use default sanitize=True configuration for ordinary HTML parsing.

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