Vulnerability · Published Aug 23, 2026 · Assigned by VulnCheck

CVE-2026-6827justhtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities

Medium 6.1

In plain English

A medium-severity cross-site scripting in justhtml from EmilStenstrom. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.1Medium

Exploit odds (30 days)0.3%top 82.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	justhtml	1.17.0	GHSA-vrx2-77f2-ww34

Affected products (as reported)

Vendor	Product	Versions
EmilStenstrom	justhtml	0 – before 1.17.0

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References

GitHub Security Advisory (GHSA-vrx2-77f2-ww34) vendor-advisory
VulnCheck Advisory: justhtml before 1.17.0 Multiple Cross-Site Scripting Vulnerabilities third-party-advisory