Emil Stenstrom justhtml up to 1.15.x Sanitization cross site scripting

Summaryinfo

A vulnerability classified as problematic has been found in Emil Stenstrom justhtml up to 1.15.x. Affected is an unknown function of the component Sanitization. The manipulation leads to cross site scripting. This vulnerability is uniquely identified as CVE-2026-6827. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Emil Stenstrom justhtml up to 1.15.x and classified as problematic. This issue affects some unknown processing of the component Sanitization. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to 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. Impacted is integrity. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-6827 since 04/21/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

Upgrading to version 1.16.0 eliminates this vulnerability.

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Productinfo

Vendor

• Emil Stenstrom

Name

• justhtml

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11
• 1.12
• 1.13
• 1.14
• 1.15

CPE 2.3info

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CPE 2.2info

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