Rule:

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Sid:
274

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Summary:
This event is generated when an attempt is made to issue a Denial of Service attack that works against some modems.

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Impact:
The system may be disconnected from it's dial-up connection.

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Detailed Information:
An ICMP Echo Request is sent to a target system with a payload that includes "+++ath".  The "+++" is an attention sequence that allows a user to enter commands to the modem.  "ath" is the modem hangup command. An ICMP Echo Reply includes the same payload as the associated request. On some modems, when the machine tries to reply to this packet, "+++ath" will be interpreted as a command and the modem will hangup.  The remote address can be spoofed.

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Affected Systems:
unknown

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Attack Scenarios:
A user can remotely cause a modem to disconnect.

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Ease of Attack:
Simple.

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False Positives:
None known.

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False Negatives:
None known.

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Corrective Action:
Set a guard time on the modem. Contact the modem manufacturer for details. A guard time will cause the modem to wait after receiving "+++". Any further input during this wait, including "ath", will be disregarded. 

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Contributors:
Original Rule Writer Unknown
Sourcefire Vulnerability Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>
Snort documentation contributed by Steven Alexander<alexander.s@mccd.edu>

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Additional References:

CVE:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=3DCAN-1999-1228

Security Focus:
http://www.securityfocus.com/archive/1/10706

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