CVE-2018-18385

Asciidoctor in versions < 1.5.8 allows remote attackers to cause a denial
of service (infinite loop). The loop was caused by the fact that
Parser.next_block was not exhausting all the lines in the reader as the
while loop expected it would. This was happening because the regular
expression that detects any list was not agreeing with the regular
expression that detects a specific list type. So the line kept getting
pushed back onto the reader, hence causing the loop.