[Snort-sigs] SID 1362

# This is a template for submitting snort signature descriptions to

Rule: alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"WEB-ATTACKS xterm command attempt"; flow:to_server,established; content:"/usr/X11R6/bin/xterm";nocase; sid:1362; classtype:web-application-attack; rev:4;)

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Sid: 1362

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Summary: A web command execution attack involving the use of a
"xterm" command

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Impact: attacker might have gained an ability to execute system commands
remotely on the system

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Detailed Information: This signature triggers when a "xterm"
command is used over a plain-text (unencrypted) connection on one of
the specified web ports to the target web server. The "xterm" command
is used to launch a terminal windows on the system with X Window
system and start an interactive session. The signature looks for the
"xterm" command in the client to web server network traffic and does
not indicate whether the command was actually successful. The presence
of the "xterm" command in the URL indicates that an attacker attempted
to trick the web server into executing system in non-interactive mode
i.e. without a valid shell session. Another case when this signature
might trigger is unencrypted HTTP tunneling connection to the server
or a shell connection through an exploit of the web server.

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Attack Scenarios: An attacker launches an "xterm" as the web server
user and then tries different local exploits to gain root.

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Ease of Attack: very easy, no exploit software required

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False Positives: none known

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False Negatives: the signature will miss the xterm launched from a different location or using the local path (./)

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Corrective Action: check the web server software for vulnerabilities
and possible upgrade the system to the latest version, also
investigate the server for signs of compromise

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Contributors: Anton Chuvakin <
http://www.chuvakin.org>

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Additional References:



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