169.254.169.254 not routing via proxy

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169.254.169.254 not routing via proxy

Postby mabhatt » Tue Oct 06, 2020 2:49 pm

Hi,

I am using CEF 3770 and facing issue while setting up the proxy. I am passing --proxy-server parameter from the command line and I see that my request are getting proxied but for 169.254.169.254 IP the request is not routing via proxy. However, when I tried opening the same in CEF 3202 it gets proxied. Am I missing something ?
mabhatt
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Re: 169.254.169.254 not routing via proxy

Postby ndesktop » Tue Oct 06, 2020 3:13 pm

169.254.0.0/16 are link local addresses and therefore will be used only in LAN and LAN broadcasts.
These are used for zeroconf, and packets from or to a private IP address (which LLAs are) cannot be routed through the public Internet, and therefore not thru a proxy as well.

The whole RFC story here.
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Re: 169.254.169.254 not routing via proxy

Postby mabhatt » Tue Oct 06, 2020 3:48 pm

I understand that its a link local address and can not be forwarded but I do not understand how does it works in CEF 3202.

I have a proxy setup and I tried opening http://169.254.169.254 with and without proxy - In the snapshot below you can see the first two rows showing the request to proxy was made and it denied the call and then next two lines without proxy.

Image

Snapshot link in case it doesn't show
https://ibb.co/MZdL6fS

The version I am currently using i.e. CEF 3770 has Network Service feature and I tried the proxy with both disabling and enabling it but no luck.
mabhatt
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Re: 169.254.169.254 not routing via proxy

Postby mabhatt » Tue Oct 06, 2020 4:17 pm

I think I found the problem -
There was a CVE for which the localhost and link-local addresses were blocked by default and in order to bypass them you will need to provide --proxy-bypass-list="<-loopback>".
Here is the issue details - https://bugs.chromium.org/p/chromium/is ... 899126#c18

The fix was made available in the following releases -
* M72 fix can be tested using the Chrome Canary (72.0.3605.0 or later)
* M71 fix can be tested using the Chrome Beta (71.0.3578.50 or later [*])

That is why I am not seeing issue in 3202.
mabhatt
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Re: 169.254.169.254 not routing via proxy

Postby ndesktop » Wed Oct 07, 2020 2:28 am

Yes, I was thinking it worked simply because of a bug.
The fix says
This aligns Chrome's behavior with the Windows and macOS proxy resolvers (but not Firefox).
So probably this is still working in Firefox.
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