IMAP/POP3 [110,995,143,993]

Footprinting the Service

By default, ports 110 and 995 are used for POP3, and ports 143 and 993 are used for IMAP. The higher ports (993 and 995) use TLS/SSL to encrypt the communication between the client and server. Using Nmap, we can scan the server for these ports. The scan will return the corresponding information (as seen below) if the server uses an embedded certificate.

Basic Nmap Scan on IMAP/POP3 Ports

z3tssu@htb[/htb]$ sudo nmap 10.129.14.128 -sV -p110,143,993,995 -sC

Starting Nmap 7.80 ( https://nmap.org ) at 2021-09-19 22:09 CEST
Nmap scan report for 10.129.14.128
Host is up (0.00026s latency).

PORT    STATE SERVICE  VERSION
110/tcp open  pop3     Dovecot pop3d
|_pop3-capabilities: AUTH-RESP-CODE SASL STLS TOP UIDL RESP-CODES CAPA PIPELINING
| ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US
| Not valid before: 2021-09-19T19:44:58
|_Not valid after:  2295-07-04T19:44:58
143/tcp open  imap     Dovecot imapd
|_imap-capabilities: more have post-login STARTTLS Pre-login capabilities LITERAL+ LOGIN-REFERRALS OK LOGINDISABLEDA0001 SASL-IR ENABLE listed IDLE ID IMAP4rev1
| ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US
| Not valid before: 2021-09-19T19:44:58
|_Not valid after:  2295-07-04T19:44:58
993/tcp open  ssl/imap Dovecot imapd
|_imap-capabilities: more have post-login OK capabilities LITERAL+ LOGIN-REFERRALS Pre-login AUTH=PLAINA0001 SASL-IR ENABLE listed IDLE ID IMAP4rev1
| ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US
| Not valid before: 2021-09-19T19:44:58
|_Not valid after:  2295-07-04T19:44:58
995/tcp open  ssl/pop3 Dovecot pop3d
|_pop3-capabilities: AUTH-RESP-CODE USER SASL(PLAIN) TOP UIDL RESP-CODES CAPA PIPELINING
| ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US
| Not valid before: 2021-09-19T19:44:58
|_Not valid after:  2295-07-04T19:44:58
MAC Address: 00:00:00:00:00:00 (VMware)

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 12.74 seconds

For example, from the output, we can see that the common name is mail1.inlanefreight.htb, and the email server belongs to the organization Inlanefreight, which is located in California. The displayed capabilities show us the commands available on the server and for the service on the corresponding port.

If we successfully figure out the access credentials for one of the employees, an attacker could log in to the mail server and read or even send the individual messages.

cURL

IMAP / POP3

z3tssu@htb[/htb]$ curl -k 'imaps://10.129.14.128' --user user:p4ssw0rd

* LIST (\HasNoChildren) "." Important
* LIST (\HasNoChildren) "." INBOX

If we also use the verbose (-v) option, we will see how the connection is made. From this, we can see the version of TLS used for encryption, further details of the SSL certificate, and even the banner, which will often contain the version of the mail server.

IMAP / POP3

z3tssu@htb[/htb]$ curl -k 'imaps://10.129.14.128' --user cry0l1t3:1234 -v

*   Trying 10.129.14.128:993...
* TCP_NODELAY set
* Connected to 10.129.14.128 (10.129.14.128) port 993 (#0)
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: /etc/ssl/certs
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
* TLSv1.3 (IN), TLS handshake, Server hello (2):
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
* TLSv1.3 (IN), TLS handshake, Certificate (11):
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
* TLSv1.3 (IN), TLS handshake, Finished (20):
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
* TLSv1.3 (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
* Server certificate:
*  subject: C=US; ST=California; L=Sacramento; O=Inlanefreight; OU=Customer Support; CN=mail1.inlanefreight.htb; emailAddress=cry0l1t3@inlanefreight.htb
*  start date: Sep 19 19:44:58 2021 GMT
*  expire date: Jul  4 19:44:58 2295 GMT
*  issuer: C=US; ST=California; L=Sacramento; O=Inlanefreight; OU=Customer Support; CN=mail1.inlanefreight.htb; emailAddress=cry0l1t3@inlanefreight.htb
*  SSL certificate verify result: self signed certificate (18), continuing anyway.
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* old SSL session ID is stale, removing
< * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] HTB-Academy IMAP4 v.0.21.4
> A001 CAPABILITY
< * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN
< A001 OK Pre-login capabilities listed, post-login capabilities have more.
> A002 AUTHENTICATE PLAIN AGNyeTBsMXQzADEyMzQ=
< * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY LITERAL+ NOTIFY SPECIAL-USE
< A002 OK Logged in
> A003 LIST "" *
< * LIST (\HasNoChildren) "." Important
* LIST (\HasNoChildren) "." Important
< * LIST (\HasNoChildren) "." INBOX
* LIST (\HasNoChildren) "." INBOX
< A003 OK List completed (0.001 + 0.000 secs).
* Connection #0 to host 10.129.14.128 left intact

To interact with the IMAP or POP3 server over SSL, we can use openssl, as well as ncat. The commands for this would look like this:

OpenSSL - TLS Encrypted Interaction POP3

IMAP / POP3

z3tssu@htb[/htb]$ openssl s_client -connect 10.129.14.128:pop3s

CONNECTED(00000003)
Can't use SSL_get_servername
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify error:num=18:self signed certificate
verify return:1
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify return:1
---
Certificate chain
 0 s:C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb

...SNIP...

---
read R BLOCK
---
Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384
    Session-ID: 3CC39A7F2928B252EF2FFA5462140B1A0A74B29D4708AA8DE1515BB4033D92C2
    Session-ID-ctx:
    Resumption PSK: 68419D933B5FEBD878FF1BA399A926813BEA3652555E05F0EC75D65819A263AA25FA672F8974C37F6446446BB7EA83F9
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - d7 86 ac 7e f3 f4 95 35-88 40 a5 b5 d6 a6 41 e4   ...~...5.@....A.
    0010 - 96 6c e6 12 4f 50 ce 72-36 25 df e1 72 d9 23 94   .l..OP.r6%..r.#.
    0020 - cc 29 90 08 58 1b 57 ab-db a8 6b f7 8f 31 5b ad   .)..X.W...k..1[.
    0030 - 47 94 f4 67 58 1f 96 d9-ca ca 56 f9 7a 12 f6 6d   G..gX.....V.z..m
    0040 - 43 b9 b6 68 de db b2 47-4f 9f 48 14 40 45 8f 89   C..h...GO.H.@E..
    0050 - fa 19 35 9c 6d 3c a1 46-5c a2 65 ab 87 a4 fd 5e   ..5.m<.F\.e....^
    0060 - a2 95 25 d4 43 b8 71 70-40 6c fe 6f 0e d1 a0 38   ..%.C.qp@l.o...8
    0070 - 6e bd 73 91 ed 05 89 83-f5 3e d9 2a e0 2e 96 f8   n.s......>.*....
    0080 - 99 f0 50 15 e0 1b 66 db-7c 9f 10 80 4a a1 8b 24   ..P...f.|...J..$
    0090 - bb 00 03 d4 93 2b d9 95-64 44 5b c2 6b 2e 01 b5   .....+..dD[.k...
    00a0 - e8 1b f4 a4 98 a7 7a 7d-0a 80 cc 0a ad fe 6e b3   ......z}......n.
    00b0 - 0a d6 50 5d fd 9a b4 5c-28 a4 c9 36 e4 7d 2a 1e   ..P]...\(..6.}*.

    Start Time: 1632081313
    Timeout   : 7200 (sec)
    Verify return code: 18 (self signed certificate)
    Extended master secret: no
    Max Early Data: 0
---
read R BLOCK
+OK HTB-Academy POP3 Server

OpenSSL - TLS Encrypted Interaction IMAP

IMAP / POP3

z3tssu@htb[/htb]$ openssl s_client -connect 10.129.14.128:imaps

CONNECTED(00000003)
Can't use SSL_get_servername
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify error:num=18:self signed certificate
verify return:1
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify return:1
---
Certificate chain
 0 s:C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb

...SNIP...

---
read R BLOCK
---
Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384
    Session-ID: 2B7148CD1B7B92BA123E06E22831FCD3B365A5EA06B2CDEF1A5F397177130699
    Session-ID-ctx:
    Resumption PSK: 4D9F082C6660646C39135F9996DDA2C199C4F7E75D65FA5303F4A0B274D78CC5BD3416C8AF50B31A34EC022B619CC633
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - 68 3b b6 68 ff 85 95 7c-8a 8a 16 b2 97 1c 72 24   h;.h...|......r$
    0010 - 62 a7 84 ff c3 24 ab 99-de 45 60 26 e7 04 4a 7d   b....$...E`&..J}
    0020 - bc 6e 06 a0 ff f7 d7 41-b5 1b 49 9c 9f 36 40 8d   .n.....A..I..6@.
    0030 - 93 35 ed d9 eb 1f 14 d7-a5 f6 3f c8 52 fb 9f 29   .5........?.R..)
    0040 - 89 8d de e6 46 95 b3 32-48 80 19 bc 46 36 cb eb   ....F..2H...F6..
    0050 - 35 79 54 4c 57 f8 ee 55-06 e3 59 7f 5e 64 85 b0   5yTLW..U..Y.^d..
    0060 - f3 a4 8c a6 b6 47 e4 59-ee c9 ab 54 a4 ab 8c 01   .....G.Y...T....
    0070 - 56 bb b9 bb 3b f6 96 74-16 c9 66 e2 6c 28 c6 12   V...;..t..f.l(..
    0080 - 34 c7 63 6b ff 71 16 7f-91 69 dc 38 7a 47 46 ec   4.ck.q...i.8zGF.
    0090 - 67 b7 a2 90 8b 31 58 a0-4f 57 30 6a b6 2e 3a 21   g....1X.OW0j..:!
    00a0 - 54 c7 ba f0 a9 74 13 11-d5 d1 ec cc ea f9 54 7d   T....t........T}
    00b0 - 46 a6 33 ed 5d 24 ed b0-20 63 43 d8 8f 14 4d 62   F.3.]$.. cC...Mb

    Start Time: 1632081604
    Timeout   : 7200 (sec)
    Verify return code: 18 (self signed certificate)
    Extended master secret: no
    Max Early Data: 0
---
read R BLOCK
* OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] HTB-Academy IMAP4 v.0.21.4

Once we have successfully initiated a connection and logged in to the target mail server, we can use the above commands to work with and navigate the server. We want to point out that the configuration of our own mail server, the research for it, and the experiments we can do together with other community members will give us the know-how to understand the communication taking place and what configuration options are responsible for this.

In the SMTP section, we have found the user robin. Another member of our team was able to find out that the user also uses his username as a password (robin:robin). We can use these credentials and try them to interact with the IMAP/POP3 services.

Curl

curl -k 'imaps://10.129.14.128' --user user:p4ssw0rd

* LIST (\HasNoChildren) "." Important
* LIST (\HasNoChildren) "." INBOX

Curl with Verbose

IMAP / POP3

z3tssu@htb[/htb]$ curl -k 'imaps://10.129.14.128' --user cry0l1t3:1234 -v

*   Trying 10.129.14.128:993...
* TCP_NODELAY set
* Connected to 10.129.14.128 (10.129.14.128) port 993 (#0)
* successfully set certificate verify locations:
*   CAfile: /etc/ssl/certs/ca-certificates.crt
  CApath: /etc/ssl/certs
* TLSv1.3 (OUT), TLS handshake, Client hello (1):
* TLSv1.3 (IN), TLS handshake, Server hello (2):
* TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8):
* TLSv1.3 (IN), TLS handshake, Certificate (11):
* TLSv1.3 (IN), TLS handshake, CERT verify (15):
* TLSv1.3 (IN), TLS handshake, Finished (20):
* TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1):
* TLSv1.3 (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
* Server certificate:
*  subject: C=US; ST=California; L=Sacramento; O=Inlanefreight; OU=Customer Support; CN=mail1.inlanefreight.htb; emailAddress=cry0l1t3@inlanefreight.htb
*  start date: Sep 19 19:44:58 2021 GMT
*  expire date: Jul  4 19:44:58 2295 GMT
*  issuer: C=US; ST=California; L=Sacramento; O=Inlanefreight; OU=Customer Support; CN=mail1.inlanefreight.htb; emailAddress=cry0l1t3@inlanefreight.htb
*  SSL certificate verify result: self signed certificate (18), continuing anyway.
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* TLSv1.3 (IN), TLS handshake, Newsession Ticket (4):
* old SSL session ID is stale, removing
< * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] HTB-Academy IMAP4 v.0.21.4
> A001 CAPABILITY
< * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN
< A001 OK Pre-login capabilities listed, post-login capabilities have more.
> A002 AUTHENTICATE PLAIN AGNyeTBsMXQzADEyMzQ=
< * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY LITERAL+ NOTIFY SPECIAL-USE
< A002 OK Logged in
> A003 LIST "" *
< * LIST (\HasNoChildren) "." Important
* LIST (\HasNoChildren) "." Important
< * LIST (\HasNoChildren) "." INBOX
* LIST (\HasNoChildren) "." INBOX
< A003 OK List completed (0.001 + 0.000 secs).
* Connection #0 to host 10.129.14.128 left intact

OpenSSL - TLS Encrypted Interaction POP3

z3tssu@htb[/htb]$ openssl s_client -connect 10.129.14.128:pop3s

CONNECTED(00000003)
Can't use SSL_get_servername
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify error:num=18:self signed certificate
verify return:1
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify return:1
---
Certificate chain
 0 s:C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb

...SNIP...

---
read R BLOCK
---
Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384
    Session-ID: 3CC39A7F2928B252EF2FFA5462140B1A0A74B29D4708AA8DE1515BB4033D92C2
    Session-ID-ctx:
    Resumption PSK: 68419D933B5FEBD878FF1BA399A926813BEA3652555E05F0EC75D65819A263AA25FA672F8974C37F6446446BB7EA83F9
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - d7 86 ac 7e f3 f4 95 35-88 40 a5 b5 d6 a6 41 e4   ...~...5.@....A.
    0010 - 96 6c e6 12 4f 50 ce 72-36 25 df e1 72 d9 23 94   .l..OP.r6%..r.#.
    0020 - cc 29 90 08 58 1b 57 ab-db a8 6b f7 8f 31 5b ad   .)..X.W...k..1[.
    0030 - 47 94 f4 67 58 1f 96 d9-ca ca 56 f9 7a 12 f6 6d   G..gX.....V.z..m
    0040 - 43 b9 b6 68 de db b2 47-4f 9f 48 14 40 45 8f 89   C..h...GO.H.@E..
    0050 - fa 19 35 9c 6d 3c a1 46-5c a2 65 ab 87 a4 fd 5e   ..5.m<.F\.e....^
    0060 - a2 95 25 d4 43 b8 71 70-40 6c fe 6f 0e d1 a0 38   ..%.C.qp@l.o...8
    0070 - 6e bd 73 91 ed 05 89 83-f5 3e d9 2a e0 2e 96 f8   n.s......>.*....
    0080 - 99 f0 50 15 e0 1b 66 db-7c 9f 10 80 4a a1 8b 24   ..P...f.|...J..$
    0090 - bb 00 03 d4 93 2b d9 95-64 44 5b c2 6b 2e 01 b5   .....+..dD[.k...
    00a0 - e8 1b f4 a4 98 a7 7a 7d-0a 80 cc 0a ad fe 6e b3   ......z}......n.
    00b0 - 0a d6 50 5d fd 9a b4 5c-28 a4 c9 36 e4 7d 2a 1e   ..P]...\(..6.}*.

    Start Time: 1632081313
    Timeout   : 7200 (sec)
    Verify return code: 18 (self signed certificate)
    Extended master secret: no
    Max Early Data: 0
---
read R BLOCK
+OK HTB-Academy POP3 Server

OpenSSL - TLS Encrypted Interaction IMAP

z3tssu@htb[/htb]$ openssl s_client -connect 10.129.14.128:imaps

CONNECTED(00000003)
Can't use SSL_get_servername
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify error:num=18:self signed certificate
verify return:1
depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb
verify return:1
---
Certificate chain
 0 s:C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb

...SNIP...

---
read R BLOCK
---
Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384
    Session-ID: 2B7148CD1B7B92BA123E06E22831FCD3B365A5EA06B2CDEF1A5F397177130699
    Session-ID-ctx:
    Resumption PSK: 4D9F082C6660646C39135F9996DDA2C199C4F7E75D65FA5303F4A0B274D78CC5BD3416C8AF50B31A34EC022B619CC633
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - 68 3b b6 68 ff 85 95 7c-8a 8a 16 b2 97 1c 72 24   h;.h...|......r$
    0010 - 62 a7 84 ff c3 24 ab 99-de 45 60 26 e7 04 4a 7d   b....$...E`&..J}
    0020 - bc 6e 06 a0 ff f7 d7 41-b5 1b 49 9c 9f 36 40 8d   .n.....A..I..6@.
    0030 - 93 35 ed d9 eb 1f 14 d7-a5 f6 3f c8 52 fb 9f 29   .5........?.R..)
    0040 - 89 8d de e6 46 95 b3 32-48 80 19 bc 46 36 cb eb   ....F..2H...F6..
    0050 - 35 79 54 4c 57 f8 ee 55-06 e3 59 7f 5e 64 85 b0   5yTLW..U..Y.^d..
    0060 - f3 a4 8c a6 b6 47 e4 59-ee c9 ab 54 a4 ab 8c 01   .....G.Y...T....
    0070 - 56 bb b9 bb 3b f6 96 74-16 c9 66 e2 6c 28 c6 12   V...;..t..f.l(..
    0080 - 34 c7 63 6b ff 71 16 7f-91 69 dc 38 7a 47 46 ec   4.ck.q...i.8zGF.
    0090 - 67 b7 a2 90 8b 31 58 a0-4f 57 30 6a b6 2e 3a 21   g....1X.OW0j..:!
    00a0 - 54 c7 ba f0 a9 74 13 11-d5 d1 ec cc ea f9 54 7d   T....t........T}
    00b0 - 46 a6 33 ed 5d 24 ed b0-20 63 43 d8 8f 14 4d 62   F.3.]$.. cC...Mb

    Start Time: 1632081604
    Timeout   : 7200 (sec)
    Verify return code: 18 (self signed certificate)
    Extended master secret: no
    Max Early Data: 0
---
read R BLOCK
* OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] HTB-Academy IMAP4 v.0.21.4

Example Usage of OpenSSL IMAP Interaction

After connecting to IMAP(s) using openssl with s_client, students first need to authenticate with the LOGIN command using the credentials robin:robin:

openssl s_client -connect STMIP:imaps
tag0 LOGIN robin robin

┌─[us-academy-1]─[10.10.14.69]─[htb-ac413848@pwnbox-base]─[~]
└──╼ [★]$ openssl s_client -connect 10.129.122.133:imaps

CONNECTED(00000003)

<SNIP>

tag0 LOGIN robin robin
tag0 OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY LITERAL+ NOTIFY SPECIAL-USE] Logged in

Then, students need to list all folders/mailboxes, and select the DEV.DEPARTMENT.INT mailbox:

Code: shell

tag1 LIST "" "*"
tag2 SELECT "DEV.DEPARTMENT.INT"

IMAP / POP3

tag1 LIST "" "*"

* LIST (\Noselect \HasChildren) "." DEV
* LIST (\Noselect \HasChildren) "." DEV.DEPARTMENT
* LIST (\HasNoChildren) "." DEV.DEPARTMENT.INT
* LIST (\HasNoChildren) "." INBOX
tag1 OK List completed (0.004 + 0.000 + 0.003 secs).
tag2 SELECT "DEV.DEPARTMENT.INT"
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permitted.
* 1 EXISTS
* 0 RECENT
* OK [UIDVALIDITY 1636414279] UIDs valid
* OK [UIDNEXT 2] Predicted next UID
tag2 OK [READ-WRITE] Select completed (0.003 + 0.000 + 0.002 secs).

At last, students need to fetch the body of email 1 that exists in the mailbox, to find out that the admin email address is the value of the sender:

Code: shell

tag3 FETCH 1 (BODY[])

IMAP / POP3

tag3 FETCH 1 (BODY[])

* 1 FETCH (BODY[] {167}
Subject: Flag
To: Robin <robin@inlanefreight.htb>
From: CTO <devadmin@inlanefreight.htb>
Date: Wed, 03 Nov 2021 16:13:27 +0200

HTB{983uzn8jmfgpd8jmof8c34n7zio}
)

Answer: {hidden}

PreviousFTP User Enumeration NextDefault Configuration

Last updated 2 months ago

z3tssu@htb[/htb]$ sudo nmap 10.129.14.128 -sV -p110,143,993,995 -sC Starting Nmap 7.80 ( https://nmap.org ) at 2021-09-19 22:09 CEST Nmap scan report for 10.129.14.128 Host is up (0.00026s latency). PORT STATE SERVICE VERSION 110/tcp open pop3 Dovecot pop3d |_pop3-capabilities: AUTH-RESP-CODE SASL STLS TOP UIDL RESP-CODES CAPA PIPELINING | ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US | Not valid before: 2021-09-19T19:44:58 |_Not valid after: 2295-07-04T19:44:58 143/tcp open imap Dovecot imapd |_imap-capabilities: more have post-login STARTTLS Pre-login capabilities LITERAL+ LOGIN-REFERRALS OK LOGINDISABLEDA0001 SASL-IR ENABLE listed IDLE ID IMAP4rev1 | ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US | Not valid before: 2021-09-19T19:44:58 |_Not valid after: 2295-07-04T19:44:58 993/tcp open ssl/imap Dovecot imapd |_imap-capabilities: more have post-login OK capabilities LITERAL+ LOGIN-REFERRALS Pre-login AUTH=PLAINA0001 SASL-IR ENABLE listed IDLE ID IMAP4rev1 | ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US | Not valid before: 2021-09-19T19:44:58 |_Not valid after: 2295-07-04T19:44:58 995/tcp open ssl/pop3 Dovecot pop3d |_pop3-capabilities: AUTH-RESP-CODE USER SASL(PLAIN) TOP UIDL RESP-CODES CAPA PIPELINING | ssl-cert: Subject: commonName=mail1.inlanefreight.htb/organizationName=Inlanefreight/stateOrProvinceName=California/countryName=US | Not valid before: 2021-09-19T19:44:58 |_Not valid after: 2295-07-04T19:44:58 MAC Address: 00:00:00:00:00:00 (VMware) Service detection performed. Please report any incorrect results at https://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 12.74 seconds

z3tssu@htb[/htb]$ curl -k 'imaps://10.129.14.128' --user cry0l1t3:1234 -v * Trying 10.129.14.128:993... * TCP_NODELAY set * Connected to 10.129.14.128 (10.129.14.128) port 993 (#0) * successfully set certificate verify locations: * CAfile: /etc/ssl/certs/ca-certificates.crt CApath: /etc/ssl/certs * TLSv1.3 (OUT), TLS handshake, Client hello (1): * TLSv1.3 (IN), TLS handshake, Server hello (2): * TLSv1.3 (IN), TLS handshake, Encrypted Extensions (8): * TLSv1.3 (IN), TLS handshake, Certificate (11): * TLSv1.3 (IN), TLS handshake, CERT verify (15): * TLSv1.3 (IN), TLS handshake, Finished (20): * TLSv1.3 (OUT), TLS change cipher, Change cipher spec (1): * TLSv1.3 (OUT), TLS handshake, Finished (20): * SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384 * Server certificate: * subject: C=US; ST=California; L=Sacramento; O=Inlanefreight; OU=Customer Support; CN=mail1.inlanefreight.htb; emailAddress=cry0l1t3@inlanefreight.htb * start date: Sep 19 19:44:58 2021 GMT * expire date: Jul 4 19:44:58 2295 GMT * issuer: C=US; ST=California; L=Sacramento; O=Inlanefreight; OU=Customer Support; CN=mail1.inlanefreight.htb; emailAddress=cry0l1t3@inlanefreight.htb * SSL certificate verify result: self signed certificate (18), continuing anyway. * TLSv1.3 (IN), TLS handshake, Newsession Ticket (4): * TLSv1.3 (IN), TLS handshake, Newsession Ticket (4): * old SSL session ID is stale, removing < * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] HTB-Academy IMAP4 v.0.21.4 > A001 CAPABILITY < * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN < A001 OK Pre-login capabilities listed, post-login capabilities have more. > A002 AUTHENTICATE PLAIN AGNyeTBsMXQzADEyMzQ= < * CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY LITERAL+ NOTIFY SPECIAL-USE < A002 OK Logged in > A003 LIST "" * < * LIST (\HasNoChildren) "." Important * LIST (\HasNoChildren) "." Important < * LIST (\HasNoChildren) "." INBOX * LIST (\HasNoChildren) "." INBOX < A003 OK List completed (0.001 + 0.000 secs). * Connection #0 to host 10.129.14.128 left intact

z3tssu@htb[/htb]$ openssl s_client -connect 10.129.14.128:pop3s CONNECTED(00000003) Can't use SSL_get_servername depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb verify error:num=18:self signed certificate verify return:1 depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb verify return:1 --- Certificate chain 0 s:C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb ...SNIP... --- read R BLOCK --- Post-Handshake New Session Ticket arrived: SSL-Session: Protocol : TLSv1.3 Cipher : TLS_AES_256_GCM_SHA384 Session-ID: 3CC39A7F2928B252EF2FFA5462140B1A0A74B29D4708AA8DE1515BB4033D92C2 Session-ID-ctx: Resumption PSK: 68419D933B5FEBD878FF1BA399A926813BEA3652555E05F0EC75D65819A263AA25FA672F8974C37F6446446BB7EA83F9 PSK identity: None PSK identity hint: None SRP username: None TLS session ticket lifetime hint: 7200 (seconds) TLS session ticket: 0000 - d7 86 ac 7e f3 f4 95 35-88 40 a5 b5 d6 a6 41 e4 ...~...5.@....A. 0010 - 96 6c e6 12 4f 50 ce 72-36 25 df e1 72 d9 23 94 .l..OP.r6%..r.#. 0020 - cc 29 90 08 58 1b 57 ab-db a8 6b f7 8f 31 5b ad .)..X.W...k..1[. 0030 - 47 94 f4 67 58 1f 96 d9-ca ca 56 f9 7a 12 f6 6d G..gX.....V.z..m 0040 - 43 b9 b6 68 de db b2 47-4f 9f 48 14 40 45 8f 89 C..h...GO.H.@E.. 0050 - fa 19 35 9c 6d 3c a1 46-5c a2 65 ab 87 a4 fd 5e ..5.m<.F\.e....^ 0060 - a2 95 25 d4 43 b8 71 70-40 6c fe 6f 0e d1 a0 38 ..%.C.qp@l.o...8 0070 - 6e bd 73 91 ed 05 89 83-f5 3e d9 2a e0 2e 96 f8 n.s......>.*.... 0080 - 99 f0 50 15 e0 1b 66 db-7c 9f 10 80 4a a1 8b 24 ..P...f.|...J..$ 0090 - bb 00 03 d4 93 2b d9 95-64 44 5b c2 6b 2e 01 b5 .....+..dD[.k... 00a0 - e8 1b f4 a4 98 a7 7a 7d-0a 80 cc 0a ad fe 6e b3 ......z}......n. 00b0 - 0a d6 50 5d fd 9a b4 5c-28 a4 c9 36 e4 7d 2a 1e ..P]...\(..6.}*. Start Time: 1632081313 Timeout : 7200 (sec) Verify return code: 18 (self signed certificate) Extended master secret: no Max Early Data: 0 --- read R BLOCK +OK HTB-Academy POP3 Server

z3tssu@htb[/htb]$ openssl s_client -connect 10.129.14.128:imaps CONNECTED(00000003) Can't use SSL_get_servername depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb verify error:num=18:self signed certificate verify return:1 depth=0 C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb verify return:1 --- Certificate chain 0 s:C = US, ST = California, L = Sacramento, O = Inlanefreight, OU = Customer Support, CN = mail1.inlanefreight.htb, emailAddress = cry0l1t3@inlanefreight.htb ...SNIP... --- read R BLOCK --- Post-Handshake New Session Ticket arrived: SSL-Session: Protocol : TLSv1.3 Cipher : TLS_AES_256_GCM_SHA384 Session-ID: 2B7148CD1B7B92BA123E06E22831FCD3B365A5EA06B2CDEF1A5F397177130699 Session-ID-ctx: Resumption PSK: 4D9F082C6660646C39135F9996DDA2C199C4F7E75D65FA5303F4A0B274D78CC5BD3416C8AF50B31A34EC022B619CC633 PSK identity: None PSK identity hint: None SRP username: None TLS session ticket lifetime hint: 7200 (seconds) TLS session ticket: 0000 - 68 3b b6 68 ff 85 95 7c-8a 8a 16 b2 97 1c 72 24 h;.h...|......r$ 0010 - 62 a7 84 ff c3 24 ab 99-de 45 60 26 e7 04 4a 7d b....$...E`&..J} 0020 - bc 6e 06 a0 ff f7 d7 41-b5 1b 49 9c 9f 36 40 8d .n.....A..I..6@. 0030 - 93 35 ed d9 eb 1f 14 d7-a5 f6 3f c8 52 fb 9f 29 .5........?.R..) 0040 - 89 8d de e6 46 95 b3 32-48 80 19 bc 46 36 cb eb ....F..2H...F6.. 0050 - 35 79 54 4c 57 f8 ee 55-06 e3 59 7f 5e 64 85 b0 5yTLW..U..Y.^d.. 0060 - f3 a4 8c a6 b6 47 e4 59-ee c9 ab 54 a4 ab 8c 01 .....G.Y...T.... 0070 - 56 bb b9 bb 3b f6 96 74-16 c9 66 e2 6c 28 c6 12 V...;..t..f.l(.. 0080 - 34 c7 63 6b ff 71 16 7f-91 69 dc 38 7a 47 46 ec 4.ck.q...i.8zGF. 0090 - 67 b7 a2 90 8b 31 58 a0-4f 57 30 6a b6 2e 3a 21 g....1X.OW0j..:! 00a0 - 54 c7 ba f0 a9 74 13 11-d5 d1 ec cc ea f9 54 7d T....t........T} 00b0 - 46 a6 33 ed 5d 24 ed b0-20 63 43 d8 8f 14 4d 62 F.3.]$.. cC...Mb Start Time: 1632081604 Timeout : 7200 (sec) Verify return code: 18 (self signed certificate) Extended master secret: no Max Early Data: 0 --- read R BLOCK * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] HTB-Academy IMAP4 v.0.21.4

┌─[us-academy-1]─[10.10.14.69]─[htb-ac413848@pwnbox-base]─[~] └──╼ [★]$ openssl s_client -connect 10.129.122.133:imaps CONNECTED(00000003) <SNIP> tag0 LOGIN robin robin tag0 OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY LITERAL+ NOTIFY SPECIAL-USE] Logged in

tag1 LIST "" "*" * LIST (\Noselect \HasChildren) "." DEV * LIST (\Noselect \HasChildren) "." DEV.DEPARTMENT * LIST (\HasNoChildren) "." DEV.DEPARTMENT.INT * LIST (\HasNoChildren) "." INBOX tag1 OK List completed (0.004 + 0.000 + 0.003 secs). tag2 SELECT "DEV.DEPARTMENT.INT" * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permitted. * 1 EXISTS * 0 RECENT * OK [UIDVALIDITY 1636414279] UIDs valid * OK [UIDNEXT 2] Predicted next UID tag2 OK [READ-WRITE] Select completed (0.003 + 0.000 + 0.002 secs).

tag3 FETCH 1 (BODY[]) * 1 FETCH (BODY[] {167} Subject: Flag To: Robin <robin@inlanefreight.htb> From: CTO <devadmin@inlanefreight.htb> Date: Wed, 03 Nov 2021 16:13:27 +0200 HTB{983uzn8jmfgpd8jmof8c34n7zio} )