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Vulnerability of Microsoft OCS: denial of service via SIP

Synthesis of the vulnerability 

An attacker can send SIP INVITE queries in order to create a denial of service in Microsoft Office Communications Server.
Impacted products: Microsoft OCS.
Severity of this bulletin: 2/4.
Creation date: 02/12/2008.
Références of this threat: CVE-2008-5180, VIGILANCE-VUL-8277.

Description of the vulnerability 

The Microsoft Office Communications Server product implements SIP (Session Initiation Protocol) used for multimedia exchanges. This protocol defines following queries:
 - INVITE : the client requests a new session
 - ACK : the server acknowledges
 - BYE : ends a session
 - etc.

When MOCS receives a special SIP INVITE query, it does not free the associated memory.

An attacker can therefore send numerous queries in order to progressively deplete the memory.
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This computer threat announce impacts software or systems such as Microsoft OCS.

Our Vigil@nce team determined that the severity of this computer vulnerability is medium.

The trust level is of type confirmed by a trusted third party, with an origin of intranet client.

A proof of concept or an attack tool is available, so your teams have to process this alert. An attacker with a technician ability can exploit this cybersecurity alert.

Solutions for this threat 

Microsoft OCS: workaround for SIP.
A workaround is to filter access to ports 5060 to 5063:
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