Prevent Firefox from sending a user-agent string in HTTP requests [closed]

I was recently experimenting with HTTP requests and got curious about user agents. In particular, I’d like to know if it’s possible to prevent a browser (in my case Firefox) from including the user agent string in requests. Now, I know there are extensions that modify the string, but that’s not what I’m looking for. I would like to know if the string can be omitted completely.

Thanks

LFI to RCE through User-Agent

I’m doing a pentest on a FreeBSD machine running CuppaCMS. Already managed to login into the CMS with admin privilege, but it only takes me to a manager menu, with some options to change some tables and stuff like that, no RCE visible escalation. So i discovered an exploit on exploit-db.com that leads to LFI, after some research i was able to do RCE through User-Agent and GET requests sending . So i’m able to read the directories and "cat" some of the files out while reading the httpd-access.log file, but i can’t run any reverse shell on the server, seems like i can’t even ‘nc’ to my machine. I managed to send a php code through the User-Agent doing the reverse shell but when i did it, the server simply crashed. Any ideas on how i could continue to explore the machine? Thanks

Abnormal User-Agent value in GET request

I came a cross some WAF logs that alert on Illegal URL Length. When I investigated the logs, I noticed weird user-agent value: 7375716F62756415670E1005007A7C68721200333F23323F770233342F2E37

I have been trying to search for this value and for that format/pattern in google without any success. It seems like some kind of hashed value.

Has anyone come across such a thing? Do you think this is some kind of covert channel attempt? or just user-agent spoofing that went wrong?

Setting user-agent

Consider a scenario where post request is completed successfully for a request with specific user-agent . I want to create a html poc for the same with the respective user-agent. If it is possible how can it be done.

I read that user-agent is not in the forbidden list as per mozilla documentation : https://developer.mozilla.org/en-US/docs/Glossary/Forbidden_header_name . So I hope it can be achieved

Why almost all free HTTP Proxy server doesn’t change the User-Agent?

I’ve created a automated test suite for proxy server. From several websites in the internet like https://free-proxy-list.net/ I get many IPs of free proxy servers. I’ve also created a own Website with JSON API to get HTTP requests header.

All requests mostly differ in values like X-Forwarded-For, Via and X-Proxy-Id. But no proxy server changes the User-Agent. Its always the User-Agent from the origin, in my case python-requests/2.20.0.

After researching I know it’s technical no problem to do this with a proxy but anyone now why no free http proxy server do it?