How does Chrome bypass proxychains proxying?

Question

I noticed that when I launch Chrome with proxychains :

$ proxychains google-chrome

every request is correctly proxied, except those sent to Google websites! For instance, when I stop the proxy configured in the proxychains conf, with my proxied Chrome I cannot access any website (err_connection_refused), except Google.

I tried the same test with Firefox: every request is proxied by proxychains, including those sent to Google.

I know there are other ways to proxy requests that would also work with Google, but I am more interested to know why the proxychains method does not work when you visit Google on Chrome.

Internally, proxychains uses the LD_PRELOAD environment variable to wrap the necessary system calls and proxy all requests transparently. I wasn't expecting Chrome to be able to bypass this wrapping. How is that possible?

Thanks!

Answer 1

Proxychains Bug/Incompatibility :

There is a bug with chrome caused apparently by the sandbox feature; check Issue 45

Proxychains Limit :

Proxychains could have leaks in many situations here are some of them as example

• Child process are not proxied (chrome as example could use many process other than the main one... Solution : a work around could be modifying the binary location)
• Socks v4 Proxys can not tunnel DNS request (Solution : use instead Socks v5)
• Incompatibility with some sandbox feature/applications, as they use kernel userspace feature to be separated from the main system, proxychains does not see/intercept their connections (Solution : combine proxychains with iptables)

Alternative :

You can try tsocks as alternative, it's often available the distro repos, apt-get install tsocks or dnf install tsocks etc.