- Description:
- An attacker crafts malicious Markdown input that, when parsed by Parsedown, generates HTML containing embedded JavaScript or other harmful HTML elements.
- This malicious HTML is then rendered by the application in a user's browser without proper output encoding.
- The attacker leverages Markdown features like links, images, or raw HTML (if enabled or bypassed sanitization) to inject the malicious code.
- Impact:
- Cross-Site Scripting (XSS) vulnerability.
- Execution of arbitrary JavaScript in the victim's browser.
- Session hijacking, cookie theft, account takeover.
- Defacement of the webpage.
- Redirection to malicious websites.
- Data theft or manipulation.
- Parsedown Component Affected:
- Core Parsing Engine (Handles Markdown syntax conversion to HTML).
- Specifically, the parsing logic for links, images, and potentially inline/block HTML elements if not handled with sufficient security considerations in the application's context.
- Risk Severity: High
- Mitigation Strategies:
- Context-Aware Output Encoding: Encode HTML entities in the output generated by Parsedown before rendering it in the browser. Use appropriate encoding functions for the output context (HTML body, attributes, etc.).
- Content Security Policy (CSP): Implement a strict CSP to limit the sources of scripts and other resources, reducing the impact of XSS.
- HTML Sanitization (Output): Sanitize the HTML output from Parsedown using a robust HTML sanitization library (e.g., HTMLPurifier) to remove or neutralize potentially harmful HTML tags and attributes after Parsedown processing.
- Regular Security Audits and Penetration Testing: Include XSS testing in security assessments.