lib/exec/fetch.php in DokuWiki before 2006-03-09e, when conf[imconvert] is configured to use ImageMagick, allows remote attackers to execute arbitrary commands via shell metacharacters in the (1) w and (2) h parameters, which are not filtered when invoking convert.
http://www.vupen.com/english/advisories/2006/3851
http://security.gentoo.org/glsa/glsa-200609-20.xml