CVE-2026-111059
Received Received - Intake

Remote Code Execution via Unsanitized Markdown in Mercury

Publication date: 2026-10-19

Last updated on: 2026-10-19

Assigner: GitHub, Inc.

Description
Mercury is a Python framework for sharing Jupyter notebooks as web applications and dashboards. From 3.0.0 until 3.2.11, mr.Markdown converts attacker-controlled Markdown to HTML without sanitizing raw HTML before assigning it to an ipywidgets.HTML sink. Event-handler attributes and other active HTML can therefore reach the DOM and execute when another user views the application. This issue is fixed in version 3.2.11.

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Meta Information

Published
2026-10-19
Last Modified
2026-10-19
Generated
2026-10-19
AI Q&A
2026-10-19
EPSS Evaluated
N/A
NVD
CVE-2026-111059
EUVD
EUVD-2026-104453

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
mljar mercury >= 3.0.0, < 3.2.11

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
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.
CWE-116 The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

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Executive Summary

This is a Stored/DOM-based Cross-Site Scripting (XSS) flaw in the Mercury library's mr.Markdown widget. It occurs because the widget renders untrusted input as raw, unsanitized HTML, allowing malicious scripts to execute in the browser of any user viewing the application. The issue affects versions 3.0.0 to 3.2.10.

Detection Guidance

To detect this vulnerability, check if your Mercury framework version is between 3.0.0 and 3.2.11. Run: pip show mercury or pip list | grep mercury. If installed, verify if mr.Markdown is used in your application to render untrusted input.

Impact Analysis

An attacker could inject malicious scripts via untrusted input (e.g., user submissions or external APIs). When other users view the affected application, the scripts execute in their browsers, potentially stealing sessions, cookies, or spoofing the UI. The attack requires no developer mistake and can be triggered by normal application code.

Compliance Impact

This XSS vulnerability could lead to unauthorized data access or modification, violating GDPR's integrity and confidentiality principles or HIPAA's safeguards for protected health information. Organizations using vulnerable versions may face compliance risks due to potential data breaches.

Mitigation Strategies

Upgrade Mercury to version 3.2.11 or later. If using mr.Markdown, ensure raw HTML is disabled by default. Add frontend sanitization or Content-Security-Policy headers. Avoid using raw HTML for untrusted content.

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