Help with Threat log SCAN: Host Sweep

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Help with Threat log SCAN: Host Sweep

L1 Bithead

I am looking for assistance interpreting a report that shows “SCAN Host sweep traffic” in my threat log. There are multiple internal sources scanning multiple destination IP addresses that I do not own. The daily number of scans detected from each source is between 2 and 10. The source machine rarely scans the same destination. Is this a low level attack trying to stay under the radar or is there an explanation that does not indicate a problem on my network? I appreciate any feedback.

Type: Scan
Name: SCAN: Host Sweep
From Zone: Inside
To Zone: Outside
Source address: Internal IP address owned by me
Destination Address: various external addresses not owned by me.
Port; 99% of the time 443. Occasionally port 80 or 22222


This screen shot show traffic during one time frame. I see various Source and Destination addresses.

sample date.PNG

This screen shot is filtered by destination address. This destination address is scanned various times from different Source addresses over the course of several days.

sample destination.PNG


I'd recommend opening a Support ticket for this.

L2 Linker

I have seen these logs too.


Not been able to figure this, but, I wonder if the alert logs are generated due to source IP meeting the interval and event threshold instead of tracking it per unique source-destinat... pair when configured to alert on the Reconnaissance Protection tab.

Ideally one gets to pick and choose the tracking mechanism when you block but not for alert.


Did anyone make progress with support on this? What did they have to say?

Host sweep will detect whenever a source attempts to hit different IP addresses on the same destination port, which if you think of it is by definition internet activity (multiple IP's hit on port 443 and 80). This means that if you enable this protection on an internal Zone with internet access, it is highly likely to trigger FP's continuously for public IP's on the internet on regular internet ports (most frequently 443 and 80).

L1 Bithead

I had to reduce the interval and increase the threshold (2 secs and 1000 IPs worked for me and should be good for most scenarios). This way you won't drop normal traffic, but anything firing up more than 500 connections per second to different servers using the same port will get dropped.

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