Configuring An Ftp Inspection Policy Map For Additional Inspection Control - Cisco FirePOWER ASA 5500 series Configuration Manual

Chapter 25 Configuring Application Layer Protocol Inspection
•
•
•
•
•
•
•

Configuring an FTP Inspection Policy Map for Additional Inspection Control

FTP command filtering and security checks are provided using strict FTP inspection for improved
security and control. Protocol conformance includes packet length checks, delimiters and packet format
checks, command terminator checks, and command validation.
Blocking FTP based on user values is also supported so that it is possible for FTP sites to post files for
download, but restrict access to certain users. You can block FTP connections based on file type, server
name, and other attributes. System message logs are generated if an FTP connection is denied after
inspection.
If you want FTP inspection to allow FTP servers to reveal their system type to FTP clients, and limit the
allowed FTP commands, then create and configure an FTP map. You can then apply the FTP map when
you enable FTP inspection according to the
To create an FTP map, perform the following steps:
(Optional) Add one or more regular expressions for use in traffic matching commands according to the
Step 1
"Creating a Regular Expression" section on page
commands described in
(Optional) Create one or more regular expression class maps to group regular expressions according to
Step 2
the
(Optional) Create an FTP inspection class map by performing the following steps.
Step 3
A class map groups multiple traffic matches. Traffic must match all of the match commands to match
the class map. You can alternatively identify match commands directly in the policy map. The
difference between creating a class map and defining the traffic match directly in the inspection policy
map is that the class map lets you create more complex match criteria, and you can reuse class maps.
To specify traffic that should not match the class map, use the match not command. For example, if the
match not command specifies the string "example.com," then any traffic that includes "example.com"
does not match the class map.
OL-10088-01
Size of RETR and STOR commands—These are checked against a fixed constant. If the size is
greater, then an error message is logged and the connection is closed.
Command spoofing—The PORT command should always be sent from the client. The TCP
connection is denied if a PORT command is sent from the server.
Reply spoofing—PASV reply command (227) should always be sent from the server. The TCP
connection is denied if a PASV reply command is sent from the client. This prevents the security
hole when the user executes "227 xxxxx a1, a2, a3, a4, p1, p2."
TCP stream editing—The security appliance closes the connection if it detects TCP stream editing.
Invalid port negotiation—The negotiated dynamic port value is checked to see if it is less than 1024.
As port numbers in the range from 1 to 1024 are reserved for well-known connections, if the
negotiated port falls in this range, then the TCP connection is freed.
Command pipelining—The number of characters present after the port numbers in the PORT and
PASV reply command is cross checked with a constant value of 8. If it is more than 8, then the TCP
connection is closed.
The security appliance replaces the FTP server response to the SYST command with a series of Xs.
to prevent the server from revealing its system type to FTP clients. To override this default behavior,
use the no mask-syst-reply command in the FTP map.
Step 3.
"Creating a Regular Expression Class Map" section on page
"Configuring Application Inspection" section on page
21-6. See the types of text you can match in the match
21-8.
Cisco Security Appliance Command Line Configuration Guide
FTP Inspection
25-5.
25-27