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TCP connect() Scanning<br />Theconnect() system call provided by your operating system is used to open a connection to every interesting port on the machine. If the port is listening, connect() will succeed, otherwise the port isn't reachable.<br />Advantage<br />Don’t need Special Privileges<br />Speed<br />Disadvantage<br />Easily detectable and filterable<br />
Advantages of syn scan<br />The TCP SYN scan never actually creates a TCP session, so isn't logged by the destination host's applications<br />Since an application session is never opened, the SYN scan is also less stressful to the application service.<br />Disadvantages of syn scan<br /><ul><li>The TCP SYN scan requires that nmap have privileged access to the system. Without privileged access, nmap can't create the raw packets necessary for this half-open connection process.</li></li></ul><li>Fin scan<br />
Least traffic scan<br />Steath Scanning - The FIN Scan (-sF), Xmas Tree Scan (-sX), and Null Scan (-sN)<br />Requires Privileged Access: YESIdentifies TCP Ports: YESIdentifies UDP Ports: NO<br />These are called "stealth" scans because they send a single frame to a TCP port without any TCP handshaking or additional packet transfers<br />NMAP response for These SCAN<br />Closed<br />Open|Filtered<br />The open|filtered result is combined because firewalls often drop these frames without a response<br />
Undetectable scan<br />The XMAS scan determines which ports are open by sending packets with invalid flag settings to a target device. It is considered a stealth scan because it may be able to bypass some firewalls and IDSes more easily than the SYN scans. The Nmap XMAS scan sends packets with the Finish (FIN), Push (PSH), and Urgent (URG) flags set.<br />Because this flag combination is invalid and should never occur in normal traffic, there is no established convention for dealing with these types of packets. Different TCP stacks will respond in different ways. Typically, closed ports will respond with a RST/ACK, and open ports will drop the packet and not respond. However, some TCP stacks will respond with RST packets from all ports, even open ports, and some systems will not respond to any packets. Personal firewalls and packet filters will also alter responses to this scan<br />
why vulnerability scan<br />Although network scanning identiﬁes active hosts, ports, services, and applications, vulnerability scanning goes one step further to identify weaknesses and vulnerabilities on a system that may be exploited by an attacker<br />
Is Nessus ideal open-source vulnerability scanner<br />Its goal to detect<br />Vulnerabilities that allow a remote cracker to control or access sensitive data on a system.<br />Misconfiguration<br />Default passwords, a few common passwords, and blank/absent passwords on some system accounts. Nessus can also call Hydra (an external tool) to launch a dictionary attack.<br />
Nessus Operation<br /> In typical operation, Nessus begins by doing a port scan with one of its four internal port scanners to determine which ports are open on the target and then tries various exploits on the open ports. The vulnerability tests, available as subscriptions, are written in NASL (Nessus Attack Scripting Language), a scripting language optimized for custom network interaction.<br />
Difference between nessus professional and home feed <br />Commercial organizations which use the Nessus vulnerability scanner must purchase a Professional Feed subscription to scan their network, obtain support, updates to their database of vulnerability checks and compliance auditing<br />A 'Home Feed' is available for free to home users, but can not be used professionally.<br />There are more features of Proffessional Feed than home feed<br />
Features of Professional feed Nessus<br />The newest Nessusplugins as soon as they are released <br />Policy Compliance Checks - to make sure every host on your network complies with your local security policy. <br />Perform an unlimited amount of complete PCI-DSS audits <br />Conduct operating system, application and SQL database configuration audits against CERT, CIS, DISA STIGs, GLBA, HIPAA, NIST SCAP FDCC, NSA and PCI standards. <br />Conduct content audits such as adult content, personally identifiable information (credit cards, SSN, etc.) corporate spreadsheets, and much more. <br />Perform web application audits of custom and embedded applications to test for cross site scripting, SQL injection and much more. <br />SCADA checks to detect and audit SCADA devices <br />Virtual Appliance - access to a download of the Tenable Appliance which includes Nessus 4 and works with VMware ESX, Server, Workstation and Fusion. <br />Access to operational and technical assistance from Tenable's experienced support staff with regards to the deployment and use of their scanners, as well as the writing of audit policies for the compliance checks or content checks.<br />