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CVE-2026-6827: justhtml

Severity

5.1 (MEDIUM)

Vendor

JUSTHTML BEFORE

Affected versions

0 through before 1.16.0

Fixed version

1.16.0

Patch status

Patched

Published

2026-08-23T14:16:53.963

Modified

2026-08-23T14:16:53.963

Why it matters

This matters because the affected product may allow code execution. Prioritize systems that are internet-facing or have privileged access to other infrastructure.

Recommended admin actions

• Review during normal vulnerability triage unless the affected system is internet-facing or business-critical.
• Compare installed versions against the affected version range in the advisory.
• Review logs for suspicious activity related to the affected application or component.

Technical summary

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 , MathML ) and mutation-XSS parser-differential payloads could survive sanitization and become active HTML after reparse; SVG filter="url(…)" and preserved 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.

View the official NVD record for CVE-2026-6827

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.