The squidclamav_check_preview_handler function in squidclamav.c in SquidClamav 5.x before 5.8 and 6.x before 6.7 passes an unescaped URL to a system command call, which allows remote attackers to cause a denial of service (daemon crash) via a URL with certain characters, as demonstrated using %0D or %0A.
https://bugs.gentoo.org/show_bug.cgi?id=428778
http://www.securityfocus.com/bid/54663
http://www.openwall.com/lists/oss-security/2012/08/16/4
http://www.openwall.com/lists/oss-security/2012/08/16/2
http://squidclamav.darold.net/news.html