Crass is a Ruby CSS parser that's fully compliant with the CSS Syntax Level 3 specification. Prior to 1.0.7, when the `:preserve_comments` option is not enabled, which is the default, Crass discards CSS comments by recursively consuming the next token. An attacker-provided stylesheet containing a very large number of adjacent comments can cause excessive recursion and trigger a `SystemStackError`, denying service to the parsing application. Preserving comments avoids this recursive path. This issue is fixed in version 1.0.7.

Affected: RubyGems: crass

### Impact

When the `:preserve_comments` option is not enabled (which is the default behavior), Crass discards CSS comments by recursively consuming the next token. An attacker who provides a stylesheet containing a very large number of adjacent comments can cause excessive recursion and trigger a `SystemStackError`.

### Patches

This is fixed in Crass 1.0.7, which no longer recurses when discarding comments.

### Workarounds

Set the `:preserve_comments` option to `true` if this is acceptable to your use case (recursion doesn't occur when comments are preserved).