Signature Detail

NETBIOS RFPoision DOS Attack

This signature detects attempts to exploit a known LSA vulnerability in Microsoft Windows NT. Attackers can send maliciously crafted packets to the LSA to choke srvsvc.dll causing services.exe to reference a bad memory location. This can crash the targeted host, resulting in a restart.

Extended Description

NT hosts are subject to a Denial of Service attack against the Local Security Authority (LSA) subsystem. The LSA system, as well as the Security Accounts Manager and certain MSRPC processes can be crashed by sending invalid data to the LsaLookupNames function of the LSA API. In order for this exploit to occur, the user must first establish a null session connection to the target host. Once a host has been impacted by this exploit, the NT system will begin to exhibit "strange behavior". Remote users will be unable to connect to the host's shares or resources, users may not be able to change their passwords, console logon to a domain will be unavailable, systems management tools such as User Manager and Server Manager will not function, and RPC dependant services using integrated security (IIS, SQL Server) will not function. Users will be unable to shutdown the server - they will receive a message stating that the current user does not have privileges to perform that function. Users connected to resources prior to the attack will still be able to access these resources. These symptoms can be delayed by disabling the automatic debug option in the Registry. To disable this, set the "Auto" value of the HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug key to "0". In this configuration, the debugger will prompt the user to continue. The symptoms of the attack will not appear until this dialog box has been cleared. This Denial of Service attack requires the machine to be "hard-booted" to reset the system to normal operation. Upon reboot, the system will function normally.

Affected Products

• Microsoft Windows NT 4.0
• Microsoft Windows NT 4.0 SP1
• Microsoft Windows NT 4.0 SP2
• Microsoft Windows NT 4.0 SP3
• Microsoft Windows NT 4.0 SP4
• Microsoft Windows NT 4.0 SP5

References

• BugTraq: 465
• CVE: CVE-1999-0721
• URL: http://support.microsoft.com/default.aspx?scid=http://support.microsoft.com:80/support/kb/articles/q231/4/57.asp&NoWebContent=1