Crass versions prior to 1.0.7 contain a vulnerability where processing a stylesheet with a large number of adjacent CSS comments causes excessive recursion, leading to a SystemStackError. This occurs when the default behavior of discarding comments is used (i.e., :preserve_comments option is false). The issue is fixed in version 1.0.7, which eliminates recursion when discarding comments. As a workaround, enabling the :preserve_comments option prevents the recursion and the error.