The default configuration of the PJL Access value in the File System External Access settings on HP LaserJet MFP printers, Color LaserJet MFP printers, and LaserJet 4100, 4200, 4300, 5100, 8150, and 9000 printers enables PJL commands that use the device's filesystem, which allows remote attackers to read arbitrary files via a command inside a print job, as demonstrated by a directory traversal attack.
http://secunia.com/advisories/42238
http://securityreason.com/securityalert/8328
http://securitytracker.com/id?1024741
http://www.exploit-db.com/exploits/15631
http://www.itrc.hp.com/service/cki/docDisplay.do?docId=emr_na-c02004333
http://www.nruns.com/_downloads/SA-2010%20003-Hewlett-Packard.pdf
http://www.securityfocus.com/bid/44882