Medium · CVSS 6.1CVE-2026-6827GHSA-VRX2-77F2-WW34

justhtml before 1.17.0 Multiple Cross-Site Scripting VulnerabilitiesCVE-2026-6827

Answer in brief

CVE-2026-6827 records a Medium severity (CVSS 6.1) vulnerability in justhtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities. The current sources do not mark it as known exploited. The current feed maps EmilStenstrom/justhtml (generic), EmilStenstrom/justhtml (generic), justhtml (pypi). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 23, 2026Updated Aug 29, 2026Source checked Oct 7, 2026First seen by HOL Aug 23, 2026Material review Aug 29, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.1
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 6.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps EmilStenstrom/justhtml (generic), EmilStenstrom/justhtml (generic), justhtml (pypi). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
EmilStenstrom/justhtmlgeneric	>=0 <1.16.0	1.16.0
EmilStenstrom/justhtmlgeneric	>=0 <1.17.0	1.17.0
justhtmlpypi	>=0 <1.17.0	1.17.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for EmilStenstrom/justhtml, EmilStenstrom/justhtml, justhtml.
Review the reported fix. Update EmilStenstrom/justhtml to 1.16.0; EmilStenstrom/justhtml to 1.17.0; justhtml to 1.17.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 29, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 23, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.