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Microsoft Windows SMB Signing Vulnerability

Microsoft Windows 2000 and XP allow SMB packets to be digitally signed. Systems can be set to allow, disallow, or require signing. When two hosts connect to initiate an SMB session, negotiation of the signing requirements occurs.

Due to a flaw in the negotiation process, it is possible to cause the signing of SMB packets to be disabled, even when it is required by the host. This could allow an attacker to modify SMB packets undetected by the receiving host.

This vulnerability would have to be exploited once for each established SMB session.