143,993 - Pentesting IMAP

Internet Message Access Protocol

As its name implies, IMAP allows you to access your email messages wherever you are; much of the time, it is accessed via the Internet. Basically, email messages are stored on servers. Whenever you check your inbox, your email client contacts the server to connect you with your messages. When you read an email message using IMAP, you aren't actually downloading or storing it on your computer; instead, you are reading it off of the server. As a result, it's possible to check your email from several different devices without missing a thing.

By default, the IMAP protocol works on two ports:

• Port 143 - this is the default IMAP non-encrypted port

• Port 993 - this is the port you need to use if you want to connect using IMAP securely

PORT    STATE SERVICE REASON
143/tcp open  imap    syn-ack

Banner grabbing

nc -nv <IP> 143
openssl s_client -connect <IP>:993 -quiet

NTLM Auth - Information disclosure

If the server supports NTLM auth (Windows) you can obtain sensitive info (versions):

root@kali: telnet example.com 143 
* OK The Microsoft Exchange IMAP4 service is ready. 
>> a1 AUTHENTICATE NTLM 
+ 
>> TlRMTVNTUAABAAAAB4IIAAAAAAAAAAAAAAAAAAAAAAA= 
+ TlRMTVNTUAACAAAACgAKADgAAAAFgooCBqqVKFrKPCMAAAAAAAAAAEgASABCAAAABgOAJQAAAA9JAEkAUwAwADEAAgAKAEkASQBTADAAMQABAAoASQBJAFMAMAAxAAQACgBJAEkAUwAwADEAAwAKAEkASQBTADAAMQAHAAgAHwMI0VPy1QEAAAAA

Or automate this with nmap plugin imap-ntlm-info.nse

IMAP Bruteforce

Syntax

Login
    A1 LOGIN username password
Values can be quoted to enclose spaces and special characters. A " must then be escape with a \
    A1 LOGIN "username" "password"

List Folders/Mailboxes
    A1 LIST "" *
    A1 LIST INBOX *
    A1 LIST "Archive" *

Create new Folder/Mailbox
    A1 CREATE INBOX.Archive.2012
    A1 CREATE "To Read"

Delete Folder/Mailbox
    A1 DELETE INBOX.Archive.2012
    A1 DELETE "To Read"

Rename Folder/Mailbox
    A1 RENAME "INBOX.One" "INBOX.Two"

List Subscribed Mailboxes
    A1 LSUB "" *

Status of Mailbox (There are more flags than the ones listed)
    A1 STATUS INBOX (MESSAGES UNSEEN RECENT)

Select a mailbox
    A1 SELECT INBOX

List messages
    A1 FETCH 1:* (FLAGS)
    A1 UID FETCH 1:* (FLAGS)

Retrieve Message Content
    A1 FETCH 2 body[text]
    A1 FETCH 2 all
    A1 UID FETCH 102 (UID RFC822.SIZE BODY.PEEK[])

Close Mailbox
    A1 CLOSE

Logout
    A1 LOGOUT

From here

CURL

Basic navigation is possible with CURL, but the documentation is light on details so checking the source is recommended for precise details.

1. Listing mailboxes (imap command LIST "" "*")

    $ curl -k 'imaps://1.2.3.4/' --user user:pass
2. Listing messages in a mailbox (imap command SELECT INBOX and then SEARCH ALL)

    $ curl -k 'imaps://1.2.3.4/INBOX?ALL' --user user:pass

   The result of this search is a list of message indicies.

   Its also possible to provide more complex search terms. e.g. searching for drafts with password in mail body:

    $ curl -k 'imaps://1.2.3.4/Drafts?TEXT password' --user user:pass

   A nice overview of the search terms possible is located here.
3. Downloading a message (imap command SELECT Drafts and then FETCH 1 BODY[])

    $ curl -k 'imaps://1.2.3.4/Drafts;MAILINDEX=1' --user user:pass

   The mail index will be the same index returned from the search operation.

It is also possible to use UID (unique id) to access messages, however it is less conveniant as the search command needs to be manually formatted. E.g.

$ curl -k 'imaps://1.2.3.4/INBOX' -X 'UID SEARCH ALL' --user user:pass
$ curl -k 'imaps://1.2.3.4/INBOX;UID=1' --user user:pass

Also, possible to download just parts of a message, e.g. subject and sender of first 5 messages (the -v is required to see the subject and sender):

$ curl -k 'imaps://1.2.3.4/INBOX' -X 'FETCH 1:5 BODY[HEADER.FIELDS (SUBJECT FROM)]' --user user:pass -v 2>&1 | grep '^<'

Although, its probably cleaner to just write a little for loop:

for m in {1..5}; do
  echo $m
  curl "imap://1.2.3.4/INBOX;MAILINDEX=$m;SECTION=HEADER.FIELDS%20(SUBJECT%20FROM)" --user user:pass
done

Shodan

• port:143 CAPABILITY

• port:993 CAPABILITY