EmilStenstrom justhtml up to 1.11.x to_html cross site scripting

Summaryinfo

A vulnerability, which was classified as problematic, has been found in EmilStenstrom justhtml up to 1.11.x. Affected by this issue is the function to_html. This manipulation causes cross site scripting. The identification of this vulnerability is CVE-2026-8445. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in EmilStenstrom justhtml up to 1.11.x. It has been declared as problematic. Affected by this vulnerability is the function to_html. The manipulation with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect integrity. The summary by CVE is:

justhtml versions <= 1.11.0 (fixed in 1.12.0) do not sufficiently escape HTML-significant characters (angle brackets) in text nodes when converting a parsed document to Markdown via to_markdown(). While a small set of Markdown metacharacters are escaped, characters such as < and > are preserved, so untrusted input that is safe in to_html() — including entity-decoded text (e.g. &lt;script&gt;) or text from RCDATA/RAWTEXT-parsed elements like <title>, <textarea>, <noscript>, and <plaintext> — can be emitted as raw HTML in the Markdown output, enabling a sanitizer bypass and potential cross-site scripting when that output is rendered.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-8445 since 05/12/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

Upgrading to version 1.12.0 eliminates this vulnerability.

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Productinfo

Vendor

• EmilStenstrom

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

Website

• Product: https://github.com/EmilStenstrom/justhtml/

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