CVE-2017-15705

A denial of service vulnerability was identified that exists in Apache
SpamAssassin before 3.4.2. The vulnerability arises with certain unclosed
tags in emails that cause markup to be handled incorrectly leading to scan
timeouts. In Apache SpamAssassin, using HTML::Parser, we setup an object
and hook into the begin and end tag event handlers In both cases, the
“open” event is immediately followed by a “close” event - even if the tag
does not close in the HTML being parsed. Because of this, we are missing
the “text” event to deal with the object normally. This can cause carefully
crafted emails that might take more scan time than expected leading to a
Denial of Service. The issue is possibly a bug or design decision in
HTML::Parser that specifically impacts the way Apache SpamAssassin uses the
module with poorly formed html. The exploit has been seen in the wild but
not believed to have been purposefully part of a Denial of Service attempt.
We are concerned that there may be attempts to abuse the vulnerability in
the future.

Bugs

• <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=908969&gt;
• <https://bugs.launchpad.net/ubuntu/+source/spamassassin/+bug/1796863&gt;