connections to localhost are forwarded through the proxy about browser-extension

[erosman]

• Which version of FoxyProxy Basic are you using?
• How are you accessing the localhost services?

Firefox should bypass proxy for localhost. 🤔

Firefox ☰ ➜ Settings ➜ General ➜ Network Settings ➜ Settings

Connections to localhost, 127.0.0.1/8, and ::1 are never proxied.

[muelli]

Edition: FoxyProxy Basic
Version: 7.5.1

I am typing localhost:8383 into the address bar and I see it doesn't connect. When I select "turn Foxyproxy off", then I can connect.

[erosman]

In that case, it appears that the Firefox proxy.onRequest bypasses the localhost restrictions.

FoxyProxy v8.0 already has Global Exclude feature which can be used (once it is released).
Please wait for FoxyProxy v8.0.

[muelli]

In that case, it appears that the Firefox proxy.onRequest bypasses the localhost restrictions.

that sounds like a bug in Firefox then, I suppose.
Do you think it's worth following up with them?

[erosman]

TBH, proxy.onRequest is an independent process. That is probably why it is not taking into account the settings set in Network settings which is a totally different process.

I am going to ask Mozilla engineers about it.

[jackyzy823]

I don't think that's Firefox's bug.

In Foxy version 7.5.1,
If you set Foxy to "use patterns with enabled proxy by patterns and order" , the Option "Do not use for localhost and intranet/private IP addresses" is taken into consideration.
Ref: https://github.com/foxyproxy/firefox-extension/blob/master/src/scripts/matcher.js#L20-L40

If you set Foxy to use the specific proxy , then Foxy will always use the proxy.
Ref: https://github.com/foxyproxy/firefox-extension/blob/a3598e1c7f0237ee50e8a13a59dec265462c38a6/src/scripts/matcher.js#L65

[erosman]

@jackyzy823 Thank you for looking into the issue.

The query posted to matrix was a general one.

If a proxy is set in Firefox, localhost will not be proxied.

Firefox ☰ ➜ Settings ➜ General ➜ Network Settings ➜ Connection Settings

Connections to localhost, 127.0.0.1/8, and ::1 are never proxied.

However, if a proxy is set via proxy.onRequest, it is reported that the localhost is proxied. i.e.
Firefox -> Proxy-server -> localhost

I can not test that currently with my set-up but if that is the case, it would not only be undesirable, but also a security concern.
Can that be confirmed?

The query is about the Firefox process and the FoxyProxy code should be irrelevant. e.g.

Normal proxy connection: Firefox -> proxy -> target
For localhost: Firefox -> disregard-proxy -> localhost

https://searchfox.org/mozilla-central/source/toolkit/system/windowsproxy/nsWindowsSystemProxySettings.cpp#127-134

        // Don't use proxy for local hosts (plain hostname, no dots)
        if (!isIpAddr && !host.Contains('.')) {
          return true;
        }

        if (host.EqualsLiteral("127.0.0.1") || host.EqualsLiteral("::1")) {
          return true;
        }

https://searchfox.org/mozilla-central/source/netwerk/test/gtest/TestProtocolProxyService.cpp#26-37

auto CheckLoopbackURLs = [&](bool expected) {
    // loopback IPs are always filtered
    spec = "http://127.0.0.1/";
    ASSERT_EQ(NS_NewURI(getter_AddRefs(url), spec), NS_OK);
    ASSERT_EQ(pps->CanUseProxy(url, 80), expected);
    spec = "http://[::1]/";
    ASSERT_EQ(NS_NewURI(getter_AddRefs(url), spec), NS_OK);
    ASSERT_EQ(pps->CanUseProxy(url, 80), expected);
    spec = "http://localhost/";
    ASSERT_EQ(NS_NewURI(getter_AddRefs(url), spec), NS_OK);
    ASSERT_EQ(pps->CanUseProxy(url, 80), expected);
  };

PS. FoxyProxy 8.0 is the most up-to-date, although not released yet.

[jackyzy823]

I think if "proxy add-ons" take over control of Proxy settings, then the settings in Firefox config would not take effect (and also it shouldn't) .

[erosman]

@jackyzy823
There are 2 main proxying API in Firefox:

• proxy.settings which sets the values of browser Connection Settings (i.e. an interface for Connection Settings)
• proxy.onRequest which is based on webRequest API and intercepts net requests

Chrome only has proxy.settings.

localhost

• proxy.settings in both Firefox and Chrome implement a default bypass/pass-through for localhost
• proxy.onRequest does not appear to have the above default bypass

The question is, should proxy.onRequest have a default bypass/pass-through for localhost or not?

[erosman]

For the time being, a default bypass/past-through for localhost is added to the FoxyProxy v8.0.

[erosman]

See also:
Bug 1854324: proxy.onRequest failure to bypass proxy for localhost