POP (Post Office Protocol) #

At a Glance #

Default Ports

POP3: 110
POP3S (POP3 over TLS or SSL): 995

POP, or POP3 (POP version 3), is an application-layer protocol used by email clients to retrieve messages from a mail server. It provides access via IP to mailboxes maintained on a server.

Because POP was designed for temporary Internet connection, clients connect, retrieve messages, store them on the client, and finally delete them from the server. Clients also have the option to leave messages on the server. By contrast, IMAP was designed to normally leave all messages on the server allowing multiple client applications as online and offline modes. ¹

Telnet #

telnet 10.0.0.3 110

Netcat #

nc -n 10.0.0.3 110

openssl ² #

openssl s_client -crlf -connect 10.0.0.3:995

Parameters

s_client: SSL/TLS client program.
-crlf: translate a line feed from the terminal into CR+LF.

NTLM Information Disclosure #

See SMTP NTLM Information Disclosure

pop3-ntlm-info NSE Script #

nmap -p 110,995 --script pop3-ntlm-info 10.0.0.3

Capabilities #

POP3 capabilities are defined in RFC2449. The CAPA command allows a client to ask a server what commands it supports and possibly any site-specific policy.

pop3-capabilities NSE Script #

nmap -p 110,995 --script pop3-capabilities 10.0.0.3

Commands #

USER    Username or mailbox.
PASS    Server/mailbox-specific password.
STAT    Number of messages in the mailbox.
LIST    [ message# ] Messages summary.
RETR    [ message# ] Retrieve selected message.
DELE    [ message# ] Delete selected message.
RSET    Reset the session. Undelete deleted messages.
NOOP    No-op. Keeps connection open.
QUIT    End session.

Note: Server responses will start either with a successful (+OK) or failed status -ERR.

POP3 Exploits Search #

Refer to Exploits Search

Contributors to Wikimedia projects. “Post Office Protocol - Wikipedia.” Wikipedia, the Free Encyclopedia, Wikimedia Foundation, Inc., 9 Sept. 2001, https://en.wikipedia.org/wiki/Post_Office_Protocol. ↩︎
OpenSSL Foundation, Inc. “/Docs/Manmaster/Man1/Openssl.Html.” OpenSSL.Org, https://www.openssl.org/docs/manmaster/man1/openssl.html. ↩︎