Using HTML-style comments in a page that will be generated or interpolated server-side before being served to the user increases the risk of exposing data that should be kept private. For instance, a developer comment or line of debugging information that's left in a page could easily (and has) inadvertently expose:

• Version numbers and host names
• Full, server-side path names
• Sensitive user data

Because every other language has its own native comment format, there is no justification for using HTML-style comments in anything other than a pure HTML or XML file.

Noncompliant Code Example

  <%
      out.write("<!-- ${username} -->");  // Noncompliant
  %>
  <!-- <% out.write(userId) %> -->  // Noncompliant
  <!-- #{userPhone} -->  // Noncompliant
  <!-- ${userAddress} --> // Noncompliant

  <!-- Replace 'world' with name --> // Noncompliant
  <h2>Hello world!</h2>

Compliant Solution

  <%-- Replace 'world' with name %>  // Compliant
  <h2>Hello world!</h2>

See

• MITRE, CWE-615 - Information Exposure Through Comments