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

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


== Ask Yourself Whether

* The comment contains sensitive information.
* The comment can be removed.


== Recommended Secure Coding Practices

It is recommended to remove the comment or change its style so that it is not output to the client.


== Sensitive Code Example

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

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


== Compliant Solution

[source,html]
----
      <%-- Replace 'world' with name --%>  // Compliant
      <h2>Hello world!</h2>
----


== See

* OWASP - https://owasp.org/www-project-top-ten/2017/A3_2017-Sensitive_Data_Exposure[Top 10 2017 Category A3 - Sensitive Data Exposure]
* CWE - https://cwe.mitre.org/data/definitions/615[CWE-615 - Information Exposure Through Comments]



ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Make sure that the HTML comment does not contain sensitive information.


'''
== Comments And Links
(visible only on this page)

=== is related to: S1531

=== on 29 Jul 2014, 11:38:41 Freddy Mallet wrote:
According to the discussion we had yesterday, do you confirm that we can remove those comments @Ann ? Thanks

=== on 29 Jul 2014, 15:46:41 Ann Campbell wrote:
\[~freddy.mallet] It's in my ToDo list to merge this with RSPEC-1531

=== on 30 Jul 2014, 20:35:52 Freddy Mallet wrote:
Feedback [~ann.campbell.2]:

* As obvious as this rule can be, I would add some "Noncompliant/Compliant" sections
* Even if this rule is classified in the "Security" category I would decrease the severity to "Minor" or "Major" as the risk to have an HTML comment containing a sensitive information remains low
* We should decide if we want to use bullet points or table for the See section

endif::env-github,rspecator-view[]
