Rule: -- Sid: 106 -- Summary: Backdoor.AckCmd is a Trojan Horse that uses TCP ACK segments to communicate. This Trojan may bypass firewalls that do not keep track of the session state in a TCP transaction. -- Impact: Possible theft of data and control of the targeted machine leading to a compromise of all resources the machine is connected to. This Trojan also has the ability to delete data, steal passwords and disable the machine. Other versions are capable of launching DDoS attacks. -- Detailed Information: This Trojan affects the following operating systems: Windows 95 Windows 98 Windows ME Windows NT Windows 2000 Windows XP No other systems are affected. This is a windows executable that does not make changes to the system registry. AckCmd is a "proof of concept" Trojan. SID Message --- ------- 106 ACKcmdC trojan scan This event is indicative of an attacker attempting to locate AckCmd servers. -- Attack Scenarios: This Trojan may be delivered to the target in a number of ways. This event is indicative of an existing infection being activated. Initial compromise can be in the form of a Win32 installation program that may use the extension ".jpg" or ".bmp" when delivered via e-mail for example. -- Ease of Attack: This is Trojan activity, the target machine may already be compromised. Updated virus definition files are essential in detecting this Trojan. -- False Positives: None Known -- False Negatives: None Known -- Corrective Action: Delete the file AckCmd.exe A machine reboot is required to clear the existing process from running in memory. In addition, the use of a firewall that correctly checks the state of a TCP session is recommended. -- Contributors: Original Rule Writer Max Vision <vision@whitehats.com> Sourcefire Research Team Brian Caswell <bmc@sourcefire.com> Nigel Houghton <nigel.houghton@sourcefire.com> -- Additional References: Whitehats arachNIDS http://www.whitehats.com/info/IDS485 ntsecurity.nu ACK Tunneling Trojans http://ntsecurity.nu/papers/acktunneling/ --