Security implications of Markdown transformations

For the next version of O2 and TeamMentor I really would like to move to a Markdown world, where the content is stored as markdown and we use a C# markdown transformer to create the HTML.

At the moment there seems to be two good C# markdown APIs:

• MarkdownSharp (which O2 already supports)
• MarkdownDeep  (you can try it live here)

My questions are:

• What are the security implications of these engines?
• How good are they at handling malicious input?
• Has there been a Thread-Model / Security review done?
• Is XSS possible?
• What other vulnerabilities exists?
• How can they be used securely?