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[EOL/EOE] How does ScreenOS handle WinNuke attack?



Article ID: KB5444 KB Last Updated: 08 Apr 2021Version: 5.0

Note: A product listed in this article has either reached hardware End of Life (EOL) OR software End of Engineering (EOE).  Refer to End of Life Products & Milestones for the EOL, EOE, and End of Support (EOS) dates.

This article explains how ScreenOS handles WinNuke attacks.

WinNuke is a DoS attack targeting any computer on the Internet running Windows. The attacker sends a TCP segment—usually to NetBIOS port 139 with the urgent (URG) flag set—to a host with an established connection. This introduces a NetBIOS fragment overlap, which causes many machines running Windows to crash.

If you enable the WinNuke attack defense SCREEN option, the security device scans any incoming Microsoft NetBIOS session service (port 139) packets. If the device observes that the URG flag is set in one of those packets, it unsets the URG flag, clears the URG pointer, forwards the modified packet, and makes an entry in the event log noting that it has blocked an attempted WinNuke attack.

To enable protection against a WinNuke attack, do either of the following, where the specified zone is that in which the attack originates:

  1. Go to Screening > Screen (Zone: select a zone name):
  2. Select WinNuke Attack Protection
  3. Click Apply.


set zone zone screen winnuke

Modification History:
2020-09-16: Article reviewed for accuracy. Minor, non-technical edits.
2021-04087: Tagged with EOL/EOE
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