File: 100000158.txt

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Rule: 

--
Sid: 
100000158

-- 
Summary: 
This event is generated when an abnormally larger number of SIP INVITE messages 
is received in a short time frame.

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Impact:
This can be an indication of a denial of service attack in progress, or simply 
a poorly configured or implemented user agent.

--
Detailed Information:
This rule is used to detect overly large numbers of SIP INVITE messages coming 
into hosts on an internal network, which may indicate a denial of service 
attack in progress. Since this traffic could also be the the result of a poorly 
configured user agent, or simply a very busy SIP proxy, careful analysis of 
both the hosts receiving and sending this traffic is required before 
determining that an attack has actually taken place.

--
Affected Systems:
Any which implement the SIP protocol.

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Attack Scenarios:
An attacker could use a script to flood a system with INVITE messages, causing 
a denial of service.

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Ease of Attack:
Simple, as SIP is a public, well-documented protocol.

--
False Positives:
Known SIP proxies may receive a high volume of legitimate INVITE requests, and 
NAT devices may appear to be sending a larger number of INVITE requests than a 
regular host. It is recommended that users whitelist known SIP proxies and NAT 
devices.

--
False Negatives:
None known.

--
Corrective Action:
Use a firewall or other access-restriction device to block unwanted messages at 
your network's border.

--
Contributors:
Jiri Markl <jiri.markl@nextsoft.cz>
Sourcefire Research Team

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Additional References
Other:

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