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Scanner Starts Fast But Slows to a Crawl

Don | Last updated: Apr 03, 2015 03:33PM UTC

I have a small website for which I'm attempting an active scan. There are about 120 items in the scan queue. It starts out quite fast for the first few minutes. But after about 10-15 minutes, the scan requests slow to a crawl. I've configured the scan queue to process 20 active threads, and am running Burp Suite via command line using the -Xmx2014m option. Looking at the Burp Suite server performance statistics I see no obvious reason for why it's so slow: server capacity: 4gb RAM (40% utilized) CPU's at 4 cores (0% utilized) java.exe - ~400mb of memory consumed / CPU utilization at 0% Yet the requests begin to slow to a crawl. I checked the web server it's targeting and its CPU utilization is 40% and memory at 50%. Any ideas why the scanning starts fast and eventually slow to a crawl?

PortSwigger Agent | Last updated: Apr 08, 2015 07:57AM UTC

It's hard to identify anything obvious that could be causing this problem. It might be worth some further investigation on memory usage. The output at Help / Diagnostics includes a real-time snapshot of memory usage, as viewed from within the Java process. Also, check whether Burp shows any relevant alerts in the alerts tab. If this only happens with one application, then it's possible that some accumulated state in the application causes it to respond more slowly. Perhaps there are network-level defenses that kick in and throttle your traffic. Another avenue to investigate is the pattern of requests being made by Burp. You can use an extension like Custom Logger to view the requests that are being made. This might identify a pattern, or point towards a particular scanned URL that triggers the problem.

Burp User | Last updated: Apr 09, 2015 09:09PM UTC

Looking at the diagnostics, I don't see anything that would point to an obvious problem. See memory usage below. There are no alerts in the Alerts tab. I'll investigate the customer logger. Additionally, when I do performance testing on the sites with something other than Burp Suite, they seem to respond without issues. So I'm back to trying to identigy what within Burp Suite is causing it to process so slowly. Total memory 451,411,968 Max memory 954,728,448 Free memory 104,717,856

PortSwigger Agent | Last updated: Apr 13, 2015 07:58AM UTC

Thanks for the update. Can you also investigate whether this happens for you with all target applications, or only this one/some? Thanks.

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