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Scanner: Custom user-agent string cannot contain colon

Jim | Last updated: Jan 29, 2021 08:27PM UTC

Hello, I'm doing crawls with various user-agents, but am running into trouble with a few because the user-agent string gets rejected because it contains a colon. Here is an example: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:85.0) Gecko/20100101 Firefox/85.0 which gives the error message "Custom user agent cannot contain colon" Is there some way I can work around this?

Ben, PortSwigger Agent | Last updated: Feb 02, 2021 10:14AM UTC

Hi Jim, We actually think this might be an issue on our side - the actual problem appears to be that Burp does not like the colon in the 'rv:85.0' part of the string (Burp will happily proxy requests from an external Firefox browser that contain variations of this User-Agent value but will not allow a custom User-Agent that contains this to be saved). Removing this part of the string allows you to save the custom User-Agent successfully. I have raised a bug so that our developers can investigate this issue with a view to fixing it. We will update this thread when we have some further news to share about any potential fix being implemented in a new Burp release.

Uthman, PortSwigger Agent | Last updated: Feb 16, 2021 04:14PM UTC