Rule:

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Sid:
1971

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Summary:
Someone has attempted a format string attack that is successful against 
the SITE EXEC command on vulnerable versions of WU-FTPD.


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Impact:
Severe; remote root compromise possible if user is running a version of 
WU-FTPD prior to 2.6.2 as root.


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Detailed Information:
This attack is a format string attack against the implementation of the 
SITE EXEC command in Washington University's ftp daemon.  This 
vulnerability was widespread, due to the widespread use of wu-ftpd in 
many of the Linux distributions. 

This is an input validation problem, as wu-ftpd is not checking the user
input that is passed directly into a format string for a printf/sprintf 
function. With specific malicious data, it is possible to overwrite the 
return address of the stack.  If properly done, when the function 
attempts to return, it will return to the overwritten return address of 
the function and it is possible to execute arbitrary commands.

If running a vulnerable version of WU-FTPD as an anonymous ftp server, 
this increases the exploitability dramatically, as the exploit must run 
after a "user" has logged into the server.  Running the server allowing 
anonymous logins means that any user, anywhere can log into the ftp 
server and run the command.

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Affected Systems:
	Multiple vendor distributions of wuftpd  2.6.1 and earlier.  

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Attack Scenarios:
Attacker logs into an anonymous ftp server, checks to see if the SITE 
EXEC command is implemented, and if it is, exploits the format string 
attack, and executing arbitrary commands on the server. In most default 
implementations of WU-FTPD the daemon was running as root and allowed 
anonymous login.  If this is the case, the attacker would now have root 
access to the system.   

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Ease of Attack:
Simple. Exploit scripts are available.

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False Positives:
None Known

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False Negatives:
None Known

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Corrective Action:
Patch all instances of WU-FTPD to the latest version, 2.6.2, as well 
disallow anonymous access to the server.

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Contributors:
Sourcefire Vulnerability Research Team
Brian Caswell <bmc@sourcefire.com>
Mike Poor <mike.poor@sourcefire.com>

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Additional References:


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