GEN:SID | 1:621 |
Message | SCAN FIN |
Summary | A tcp packet with only it's FIN flag set was detected.
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Impact | Information regarding firewall rulesets, open/closed ports, ACLs, and possibly even OS type may be disclosed. This technique can also be used to bypass certain firewalls or traffic filtering/shaping devices.
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Detailed Information | A tcp packet with only it's FIN flag set was detected. Most Windows machines will respond with an ACK-RST regardless of whether or not the port is open. Most *nix systems will respond with an ACK-RST if the port is closed and will not respond at all if the port is open. Actual responses may vary.
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Affected Systems | |
Attack Scenarios | As part of information gathering leading up to another (more directed) attack, an attacker may attempt to figure out what ports are open/closed on a remote machine.
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Ease of Attack | Intermediate. To initiate an attack of this type, an attacker either needs a tool that can send packets with only the FIN flag set or the ability to craft their own packets. The former is easy, the later requires a more advanced skillset.
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Corrective Action | Determine if this particular port would have responded as being open or closed. If open, watch for more attacks on this particular service or from the remote machine that sent the packet. If closed, simply watch for more traffic from this host. Consider filtering this type of traffic at the ingress points of your network.
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Additional References | |
Rule References | arachnids: 27
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