CVE-2026-111059: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in mljar mercury

The vulnerability CVE-2026-111059 affects the mljar mercury Python framework for sharing Jupyter notebooks as web applications. Specifically, from versions 3.0.0 up to but not including 3.2.11, the mr.Markdown component improperly neutralizes input by converting Markdown containing raw HTML directly to HTML without sanitization. This unsanitized HTML is assigned to an ipywidgets.HTML sink, enabling execution of active HTML elements such as event-handler attributes when rendered in a user's browser. This constitutes a cross-site scripting (XSS) vulnerability classified under CWE-79 and CWE-116. The vulnerability is resolved in version 3.2.11.

An attacker can inject malicious HTML and JavaScript code via Markdown input that is rendered by the vulnerable mr.Markdown component. When other users view the affected application, the injected code can execute in their browsers, potentially leading to information disclosure or session hijacking. The CVSS v3.1 base score is 6.1 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, user interaction required, scope changed, and low confidentiality and integrity impact with no availability impact.

Upgrade mljar mercury to version 3.2.11 or later, where the vulnerability is fixed by properly sanitizing raw HTML in Markdown before rendering. No other mitigations are indicated by the vendor advisory. Users should apply this official fix to prevent exploitation.