Re: Intent to implement and ship: Ignore navigation to unknown protocol
On 3/29/20 9:11 AM, Emilio Cobos Álvarez wrote: Doing a bit of digging, https://bugzilla.mozilla.org/show_bug.cgi?id=680300 contains some more interesting context... We apparently used to sync-throw when assigning location.href to an unknown protocol URI in the past, there we changed it to silently fail, and now it is navigating to an error page... I'll try to look at when behavior changed around here... Though the sync-throwing clearly makes no sense as it doesn't account for redirects or what not. Apparently the pre-firefox63 behavior was to both navigate and throw... So not all that much to dig in, that was just obviously wrong, but didn't address the fingerprinting angle other than patching one of the holes. On 3/29/20 8:23 AM, Emilio Cobos Álvarez wrote: Hey, a quick web-observable change that may deserve a bit more visibility / an intent. I'd welcome some feedback, specially from the fingerprinting / privacy angle (where I'm clearly not an expert). Summary: A page redirecting / navigating to an unknown protocol will be silently ignored (and logged to the DevTools console) instead of showing an error page. This is not amazing, but it's needed because it causes a bunch of compat issues (see the list of issues in the bug below). There are a few subtle problems here. Part of the issue is that authors don't have a cross-browser way of detecting whether a protocol will be handled externally (that is, whether an app is installed to handle a given protocol). They technically can in Firefox (see example below). It's unclear whether we want to expose more than that, or that at all. Given Chrome just ignores the navigation if they can't handle it, some authors (who don't seem to test on other browsers ;)) just spam the redirect (using various methods like the location href setter / meta refresh / whatevs). This works just fine in Chromium-based browsers, but not in Firefox or Safari, which will just show an error, which causes a very frustrating experience for users. As far as I know, this behavior doesn't really expose more information than we were exposing before. In a test-case like: we have different behavior also before this patch: the contentDocument for the handled-protocol iframe will be accessible to content, and be about:blank. The contentDocument for the unhandled protocol will be the error page, which will not be accessible to content and thus be null. Other browsers seem to do about:blank for both iframes, but you can also detect this in all browsers via window.open instead (there may be other ways around it too, haven't dug all that much). Chrome insta-closes the handled protocol window (so you can check window.closed). Firefox / Safari will leave about:blank in that window, and show an error document for the second (which will throw a security error on access). So I don't think this change introduces a new privacy hole. That being said, this all seems a bit sad, and a somewhat-serious potential fingerprinting factor. I was in fact a bit nervous about this change before realizing we were already exposing this information in other (even simpler to test) ways... But I'm clearly not an expert on this matter. There are mitigations possible both for the ignored-navigation case (maybe only ignore the navigation to an unknown protocol once per document or something, and only for browsing contexts that can't be accessed by any ancestor JS? not sure) and the iframe case (probably just not show error pages in frames?). Please let me know if I you think I should file this and follow-up on it. Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1528305 Standard: https://html.spec.whatwg.org/#process-a-navigate-url-scheme allows for both the old and new behavior, as far as I (and Anne) can tell. This uses urls after redirect and so on so beforeunload and such will fire. This matches the behavior of Chromium browsers. Preference: dom.no_unknown_protocol_error.enabled (I could've sweated it a bit more). Devtools bug: N/A, ignored navigations get logged to the console. Other browsers: Chromium browsers do this, but WebKit doesn't seem to. This was causing compat issues, specially on Android, but also desktop (see above). web-platform-tests: Spec allows both behaviors, so I've added an internal test for now. Furthermore it's not clear if we want to do this for sub-windows, which my patch does, so I may need to tweak the test or add an internal switch depending on the outcome of the discussion here. Secure contexts: not restricted to secure contexts, this is a compat hack, of sorts... Is this feature enabled by default in sandboxed iframes? Not sure if the question quite applies to this, but we don't special-case sandboxed iframes here. This doesn't expose anything you couldn't do before, as discussed above. Thanks for reading all the way until here -- Emilio
Re: Intent to implement and ship: Ignore navigation to unknown protocol
Doing a bit of digging, https://bugzilla.mozilla.org/show_bug.cgi?id=680300 contains some more interesting context... We apparently used to sync-throw when assigning location.href to an unknown protocol URI in the past, there we changed it to silently fail, and now it is navigating to an error page... I'll try to look at when behavior changed around here... Though the sync-throwing clearly makes no sense as it doesn't account for redirects or what not. -- Emilio On 3/29/20 8:23 AM, Emilio Cobos Álvarez wrote: Hey, a quick web-observable change that may deserve a bit more visibility / an intent. I'd welcome some feedback, specially from the fingerprinting / privacy angle (where I'm clearly not an expert). Summary: A page redirecting / navigating to an unknown protocol will be silently ignored (and logged to the DevTools console) instead of showing an error page. This is not amazing, but it's needed because it causes a bunch of compat issues (see the list of issues in the bug below). There are a few subtle problems here. Part of the issue is that authors don't have a cross-browser way of detecting whether a protocol will be handled externally (that is, whether an app is installed to handle a given protocol). They technically can in Firefox (see example below). It's unclear whether we want to expose more than that, or that at all. Given Chrome just ignores the navigation if they can't handle it, some authors (who don't seem to test on other browsers ;)) just spam the redirect (using various methods like the location href setter / meta refresh / whatevs). This works just fine in Chromium-based browsers, but not in Firefox or Safari, which will just show an error, which causes a very frustrating experience for users. As far as I know, this behavior doesn't really expose more information than we were exposing before. In a test-case like: we have different behavior also before this patch: the contentDocument for the handled-protocol iframe will be accessible to content, and be about:blank. The contentDocument for the unhandled protocol will be the error page, which will not be accessible to content and thus be null. Other browsers seem to do about:blank for both iframes, but you can also detect this in all browsers via window.open instead (there may be other ways around it too, haven't dug all that much). Chrome insta-closes the handled protocol window (so you can check window.closed). Firefox / Safari will leave about:blank in that window, and show an error document for the second (which will throw a security error on access). So I don't think this change introduces a new privacy hole. That being said, this all seems a bit sad, and a somewhat-serious potential fingerprinting factor. I was in fact a bit nervous about this change before realizing we were already exposing this information in other (even simpler to test) ways... But I'm clearly not an expert on this matter. There are mitigations possible both for the ignored-navigation case (maybe only ignore the navigation to an unknown protocol once per document or something, and only for browsing contexts that can't be accessed by any ancestor JS? not sure) and the iframe case (probably just not show error pages in frames?). Please let me know if I you think I should file this and follow-up on it. Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1528305 Standard: https://html.spec.whatwg.org/#process-a-navigate-url-scheme allows for both the old and new behavior, as far as I (and Anne) can tell. This uses urls after redirect and so on so beforeunload and such will fire. This matches the behavior of Chromium browsers. Preference: dom.no_unknown_protocol_error.enabled (I could've sweated it a bit more). Devtools bug: N/A, ignored navigations get logged to the console. Other browsers: Chromium browsers do this, but WebKit doesn't seem to. This was causing compat issues, specially on Android, but also desktop (see above). web-platform-tests: Spec allows both behaviors, so I've added an internal test for now. Furthermore it's not clear if we want to do this for sub-windows, which my patch does, so I may need to tweak the test or add an internal switch depending on the outcome of the discussion here. Secure contexts: not restricted to secure contexts, this is a compat hack, of sorts... Is this feature enabled by default in sandboxed iframes? Not sure if the question quite applies to this, but we don't special-case sandboxed iframes here. This doesn't expose anything you couldn't do before, as discussed above. Thanks for reading all the way until here -- Emilio ___ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform ___ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
Intent to implement and ship: Ignore navigation to unknown protocol
Hey, a quick web-observable change that may deserve a bit more visibility / an intent. I'd welcome some feedback, specially from the fingerprinting / privacy angle (where I'm clearly not an expert). Summary: A page redirecting / navigating to an unknown protocol will be silently ignored (and logged to the DevTools console) instead of showing an error page. This is not amazing, but it's needed because it causes a bunch of compat issues (see the list of issues in the bug below). There are a few subtle problems here. Part of the issue is that authors don't have a cross-browser way of detecting whether a protocol will be handled externally (that is, whether an app is installed to handle a given protocol). They technically can in Firefox (see example below). It's unclear whether we want to expose more than that, or that at all. Given Chrome just ignores the navigation if they can't handle it, some authors (who don't seem to test on other browsers ;)) just spam the redirect (using various methods like the location href setter / meta refresh / whatevs). This works just fine in Chromium-based browsers, but not in Firefox or Safari, which will just show an error, which causes a very frustrating experience for users. As far as I know, this behavior doesn't really expose more information than we were exposing before. In a test-case like: we have different behavior also before this patch: the contentDocument for the handled-protocol iframe will be accessible to content, and be about:blank. The contentDocument for the unhandled protocol will be the error page, which will not be accessible to content and thus be null. Other browsers seem to do about:blank for both iframes, but you can also detect this in all browsers via window.open instead (there may be other ways around it too, haven't dug all that much). Chrome insta-closes the handled protocol window (so you can check window.closed). Firefox / Safari will leave about:blank in that window, and show an error document for the second (which will throw a security error on access). So I don't think this change introduces a new privacy hole. That being said, this all seems a bit sad, and a somewhat-serious potential fingerprinting factor. I was in fact a bit nervous about this change before realizing we were already exposing this information in other (even simpler to test) ways... But I'm clearly not an expert on this matter. There are mitigations possible both for the ignored-navigation case (maybe only ignore the navigation to an unknown protocol once per document or something, and only for browsing contexts that can't be accessed by any ancestor JS? not sure) and the iframe case (probably just not show error pages in frames?). Please let me know if I you think I should file this and follow-up on it. Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1528305 Standard: https://html.spec.whatwg.org/#process-a-navigate-url-scheme allows for both the old and new behavior, as far as I (and Anne) can tell. This uses urls after redirect and so on so beforeunload and such will fire. This matches the behavior of Chromium browsers. Preference: dom.no_unknown_protocol_error.enabled (I could've sweated it a bit more). Devtools bug: N/A, ignored navigations get logged to the console. Other browsers: Chromium browsers do this, but WebKit doesn't seem to. This was causing compat issues, specially on Android, but also desktop (see above). web-platform-tests: Spec allows both behaviors, so I've added an internal test for now. Furthermore it's not clear if we want to do this for sub-windows, which my patch does, so I may need to tweak the test or add an internal switch depending on the outcome of the discussion here. Secure contexts: not restricted to secure contexts, this is a compat hack, of sorts... Is this feature enabled by default in sandboxed iframes? Not sure if the question quite applies to this, but we don't special-case sandboxed iframes here. This doesn't expose anything you couldn't do before, as discussed above. Thanks for reading all the way until here -- Emilio ___ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
