PHP 3 and 4 do not properly cleanse user-injected format strings, which allows remote attackers to execute arbitrary commands by triggering error messages that are improperly written to the error logs.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5359
http://www.redhat.com/support/errata/RHSA-2000-095.html
http://www.redhat.com/support/errata/RHSA-2000-088.html
http://www.linux-mandrake.com/en/security/MDKSA-2000-062.php3?dis=7.1
http://www.calderasystems.com/support/security/advisories/CSSA-2000-037.0.txt
http://www.atstake.com/research/advisories/2000/a101200-1.txt
http://archives.neohapsis.com/archives/bugtraq/2000-10/0204.html