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[Archive] IDP Signature Pattern for SMTP:COMMAND:HELP



Article ID: KB4449 KB Last Updated: 13 Aug 2010Version: 4.0
IDP Signature Pattern for SMTP:COMMAND:HELP


The signature (SMTP:COMMAND:HELP) will look for the following pattern:

[( |\x09\x)*\[help\].*] in the [smtp-command-line]


The [( |\x09\x)*\[help\].*] pattern literally means:

Look for zero or more spaces or tab characters followed by a case-insensitive help and then followed by anything along a SMTP command line. Since a tab character is difficult to differentiate from multiple spaces, we typically use the hexadecimal equivalent.

\x09 is a tab that you cannot see on the command line. It is either ( ) or (\x 09 \x) followed by a star, which means the line must begin with zero or more spaces or tabs, and then the command HELP.

SMTP is not an interactive protocol. Anyone sending HELP in the middle of a server-to-server communication means that they are trying to send SMTP by hand. It is not desirable to allow this, and it may be best to close connection for this type of traffic.

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