Various PDF viewers including (1) Adobe Acrobat 5.06 and (2) Xpdf 1.01 allow remote attackers to execute arbitrary commands via shell metacharacters in an embedded hyperlink.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A664
http://www.redhat.com/support/errata/RHSA-2003-197.html
http://www.redhat.com/support/errata/RHSA-2003-196.html
http://www.mandriva.com/security/advisories?name=MDKSA-2003:071
http://www.kb.cert.org/vuls/id/200132
http://secunia.com/advisories/9038
http://secunia.com/advisories/9037
http://marc.info/?l=bugtraq&m=105777963019186&w=2
http://lists.grok.org.uk/pipermail/full-disclosure/2003-June/005719.html