client/cl_parse.c in the id3 Quake 3 Engine 1.32c and the Icculus Quake 3 Engine (ioquake3) revision 810 and earlier allows remote malicious servers to overwrite arbitrary write-protected cvars variables on the client, such as cl_allowdownload for Automatic Downloading and fs_homepath for the quake3 path, via a string of cvar names and values sent from the server. NOTE: this can be combined with another vulnerability to overwrite arbitrary files.
aluigi.altervista.org/adv/q3cfilevar-adv.txt
secunia.com/advisories/20401
secunia.com/advisories/20851
securityreason.com/securityalert/1171
www.securityfocus.com/archive/1/438515/100/0/threaded
www.securityfocus.com/archive/1/438660/100/0/threaded
www.securityfocus.com/bid/18685
www.vupen.com/english/advisories/2006/2569
exchange.xforce.ibmcloud.com/vulnerabilities/26889
exchange.xforce.ibmcloud.com/vulnerabilities/27486