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Canary Variable dependent Payload

Tehreem | Last updated: Apr 23, 2021 07:41AM UTC

Hello there, I’m using burp pro version, and while running an active scan burp returns the following issue. Issue detail The User-Agent HTTP header appears to be vulnerable to server-side JavaScript code injection attacks. The submitted value appears to be placed into a dynamically evaluated JavaScript statement, within a single-quoted context. The payload '+(function(){if(typeof wwgk2==="undefined"){var a=new Date();do{var b=new Date();}while(b-a<20000);wwgk2=1;}}())+' was submitted in the User-Agent HTTP header. The application took 34591 milliseconds to respond to the request, compared with 0 milliseconds for the original request, indicating that the injected JavaScript code caused a time delay. Uptill here I know what’s happening. But the following line makes no sense to me and I find no resource over the internet that can indicate or explain about reproducing this type of error and why it is asking to change the canary variable. Please note that to manually reproduce this behavior using the reported request, you will need to change the name of the canary variable, which is currently wwgk2. Any explanation or link to the resource would be highly appreciated. Thank you in advance!

Michelle, PortSwigger Agent | Last updated: Apr 23, 2021 01:18PM UTC