Rule:

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Sid:
1444

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Summary
This event is generated when a TFTP GET request is made.  This is an 
indication that someone is attempting to download a file on the server.

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Impact
A TFTP GET requests allows a remote attacker to download files on the 
TFTP server.  If the TFTP server allows anonymous TFTP GET requests it 
is possible to download any of the published files on the server..

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Detailed Information
This rule will generate an event on in-bound TFTP GET requests.  A TFTP 
GET request is generated when an attempt to download a file from the 
server is initiated.

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Attack Scenarios
Attackers may use TFTP to upload and download files from server that are
properly or improperly configured.  Normally attackers attempt to locate
TFTP servers using automated scanners and tools.  Once a TFTP server is 
located an attempt to write files and get files from the TFTP server is 
made.  Depending on the results of those tests attackers may attempt to 
further exploit that system, by overwriting system files or downloading 
password files to access the system.

Cisco ONS platforms allow unauthenticated access to files via TFTP. This
event may be generated when an attempt is made to access files on a 
Cisco device using TFTP.

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Ease of Attack
Simple: Numerous tools and automated scripts exist for scanning large
subnets for improperly configured TFTP servers.

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False Positives
Legitimate TFTP GET requests for polling routers or other network
devices may trigger this rule.  

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False Negatives
None known

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Corrective Action
The TFTP server should be configured to only allow GET requests from
trusted locations.

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Contributors
Original rule writer unknown
Sourcefire Research Team
Matthew Watchinski <Matt.Watchinski@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References

CVE:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-1999-0183

Arachnids:
http://www.whitehats.com/info/IDS148

Bugtraq:
http://www.securityfocus.com/bid/9699

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