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Burp fails loading CSS, responds extremely sluggish, CPU up to 100%

Daniel | Last updated: Sep 07, 2016 09:47AM UTC

Hi, I am using Burp on a Mac Book Pro (End 2013, 16 GB Ram) latest version (1.7.05). Burp has come to a point, that I can hardly use it for my day to day work: When doing an application test with Burp and Firefox (most recent, 48.0.2 at this time), the connection via burp is quite slow (and gets slower over time), and the browser fails to display CSS scripts. Also, every now and then, the CPU of the Burp process goes up to 100%, rendering the proxy unusable. This happens randomly - sometimes immediately after start or after a couple of hours. Unfortunately I was not able to find a root cause for this behavior - it simply happens over time. I have tried to reduce load by disabling all live scanning features completely. I have also killed both, Burp and Firefox, but even after a fresh restart (and resetting all configuration settings in Burp to default) this problem still exists. I did have similar problems with older versions of Burp, but assumed that was an JRE issue - now that the JRE comes bundled with Burp, the problem still remains. At this point, i can not use Burp anymore, as the the proxy reacts very, very sluggish and no CSS files are loaded right from the start. I have also tried and emptied the cache in Firefox. I have already loaded the Burp CA in Firefox, so this seems not to be a SSL issue either. Am I missing something? Is this known behavior, and if yes: Is there anything I can do to get Burp back working? I am quit desperate here getting work done with a non-functional proxy :/

Burp User | Last updated: Sep 07, 2016 11:29AM UTC

Could be my bad: I was using the "JS Beautifier" extension. Deactivated it, everything seems to be back to normal, at least the CSS loads - seems like a buggy extension. I really hope that was the problem as it was getting really, really annoying.

PortSwigger Agent | Last updated: Sep 07, 2016 12:31PM UTC

Thanks for the update. Do let us know if the problem reappears when you aren't using that extension.

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