Why does headers-normalize-response.htm expect null bytes to be allowed? #165

wisniewskit · 2017-10-16T03:21:35Z

Per spec (first line is from the XHR spec; others are from Fetch spec which it links to):

A request has an associated header list (a header list). Unless stated otherwise it is empty.
A header list consists of zero or more headers.
A header consists of a name and value.
A value is a byte sequence that matches the following conditions:

Has no leading or trailing HTTP whitespace bytes.

Contains no 0x00, 0x0A or 0x0D bytes.

Apparently only Firefox goes against the spec and supports null bytes for XMLHttpRequests (but not Fetch in general): https://wptdashboard.appspot.com/XMLHttpRequest/headers-normalize-response.htm

Should the tests be changed to reflect the spec, or the spec (and other browsers) updated to match Firefox?

annevk · 2017-10-16T07:54:46Z

Hmm, that's for setting header values. I'm not sure response header values were fully considered. Sigh.

Dropping the header completely makes some sense (the null results), but would require changes to Chrome as well.

cc @mnot @tyoshino @yutakahirano

mnot · 2017-10-19T05:40:36Z

FWIW, corresponding HTTP spec is field-value:
http://httpwg.org/specs/rfc7230.html#header.fields

VCHAR gets you 0x21-7E, field-content adds in 0x20 and 0x09, and obs-text gets you 0x80-FF.

obs-fold gets you 0x0A and 0x0D in certain patterns (but you can also add that they're automagically folded in, which probably makes the best sense).

That means HTTP doesn't like 0x00-09 and 0x0A-1F.

Anybody have data about how often they're seen in the wild?

annevk · 2017-10-19T07:48:37Z

@mnot see httpwg/http-core#19 and whatwg/fetch#332 for how the new field-value is broken. I suspect the same might go for other places where the HTTP revision started to ban C0 controls.

yutakahirano · 2017-10-20T03:44:12Z

@davidben Probably you know more why Chrome behaves in the current way.

davidben · 2017-10-20T05:23:28Z

I don't know anything about this stuff, sorry. (Also not sure what the current behavior is to begin with... ask git log or mmenke? Dunno what his Github is.)

wisniewskit · 2018-02-18T04:27:16Z

@RByers, is there anyone we could ping to help figure this Blink XHR quirk out?

annevk · 2018-04-11T10:39:40Z

@MattMenke2 @bencebeky any thoughts on this?

bencebeky · 2018-04-11T10:56:36Z

My gut feeling is that (1) if no other browsers support null bytes, then it is probably safe for Firefox to reject them too, and (2) it might be less error-prone if the requirements for headers for XMLHttpRequests were consistent with the requirements for other requests. Other that this, I do not have strong feelings, and am happy to change Chrome behavior if there is a compelling use case.

annevk · 2018-04-11T11:19:07Z

@bencebeky thanks for the quick reply! I think the main problem with Chrome's behavior at the moment is that it strips 0x00 from header values. It doesn't reject anything.

http://w3c-test.org/xhr/headers-normalize-response.htm was added in https://bugzilla.mozilla.org/show_bug.cgi?id=1277019 and apparently Safari also passes all tests.

From that bug it seems this was already tested in http://w3c-test.org/cors/allow-headers.htm which reveals some minor security implications. (Disregarding the response or response header would also work for that specific case.)

The simplest solution based on this is probably accepting that response header values can contain 0x00 (at least when going over the network, no need to add support for this to Response objects and such). Rejecting headers or responses that have headers whose values contain 0x00 seems more involved (as it would require changing all clients), but doable if there's enough willingness.

(I also looked at Edge and it simply seems to hang on loading the page, which doesn't seem great. @travisleithead you might want to look at that.)

bencebeky · 2018-04-11T11:32:58Z

I understand. Indeed stripping characters seems fragile.

What is the plan with the Fetch spec? Is it going to be changed to allow null characters in header values? Or changed to require that such header fields are ignored?

annevk · 2018-04-11T11:59:33Z

@bencebeky well, I tried to solicit a plan with the above comment. I think the easiest would be to allow response headers to contain 0x00, but never include them in request headers and never allow 0x00 to be set through the API. @jakearchibald or would that be problematic for service workers if you wanted to forward a response that included 0x00 in header values?

jakearchibald · 2018-04-11T12:11:37Z

@annevk how would a request with a header like this show up in a service worker?

Rejecting headers or responses that have headers whose values contain 0x00 seems more involved

At what point would it be rejected, and what kind of rejection would it be?

bencebeky · 2018-04-11T12:14:50Z

It seems inconsistent to allow null characters in responses and not in requests. Why not stick to the current specification and disallow them in both? In any case, I agree that Chrome's current behavior is not optimal.

What is currently done with requests that have null bytes? Are the header fields ignored, or the whole request rejected with an error? If they are rejected, could responses be rejected with a similar error? If they are happily accepted, maybe the spec could reflect that.

Are you aware of a use case that would justify the need to accept headers with null characters?

annevk · 2018-04-11T12:25:30Z

@jakearchibald it would only be a response. (If we go with rejection, we'd probably have to treat it as a network error. Only dropping the header seems too dangerous.)

@bencebeky there's no way that I know of whereby you can set a request header value that contains a 0x00 from anywhere within the web platform. API-wise there's no way for response header values either, but I had forgotten to test this scenario (whereby the server sets it).

bencebeky · 2018-04-11T12:31:28Z

Okay, so it seems like it makes sense to disallow null bytes in request headers. For consistency, it would make sense to do the same in response headers, both XHR and otherwise. I agree that network error would be the best choice, otherwise there would remain server deployments that send null bytes and we would be stuck with having to support them forever.

annevk · 2018-04-11T12:49:29Z

Okay, I definitely support trying that out. I'll create a PR for web-platform-tests changes, will file bugs against Edge, Firefox, and Safari, and report back. I take it you're willing to take care of Chrome?

bencebeky · 2018-04-11T12:57:08Z

Yes, I'll take care of Chrome. Thank you for driving this!

As discussed in whatwg/xhr#165 these should turn the response into a network error.

annevk · 2018-04-11T13:15:56Z

Updated tests: web-platform-tests/wpt#10424.

Bugs:

MattMenke2 · 2018-04-11T13:19:51Z

I'm a bit late to respond, but I agree with this decision - rejecting headers with nulls seems the safest option here. We should also add code to Chrome's code, either in net/ or in services/network, to reject requests with nulls in headers, to prevent compromised renderers sending headers with nulls in them.

…

On Wed, Apr 11, 2018 at 9:15 AM, Anne van Kesteren ***@***.*** > wrote: Updated tests: web-platform-tests/wpt#10424 <web-platform-tests/wpt#10424>. Bugs: - https://bugzilla.mozilla.org/show_bug.cgi?id=1453318 - https://bugs.webkit.org/show_bug.cgi?id=184493 - https://developer.microsoft.com/en-us/microsoft-edge/ platform/issues/16880179/ — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#165 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AUBj8bnPQFa35UNA6-7gxQyljLlnfiMQks5tngIOgaJpZM4P6CbD> .

bencebeky · 2018-04-12T14:31:30Z

Didn't find bug against Chromium, so just filed https://crbug.com/832086.

As discussed in whatwg/xhr#165 these should turn the response into a network error.

annevk · 2018-08-28T06:10:03Z

The tests finally landed. It seems no implementation has been updated so far. I guess the one thing that remains here is clarify somewhere that if an HTTP response header value contains a 0x00 a network error is to be returned?

…ntaining 0x00, a=testonly Automatic update from web-platform-testsFetch/XHR: response header value containing 0x00 As discussed in whatwg/xhr#165 these should turn the response into a network error. -- wpt-commits: 3d172bc612e03a896b5611d9e9652f860995feef wpt-pr: 10424

While the HTTP spec further limits what values are legal, nulls are particularly concerning, and it's safest just to reject them. See discussion here: whatwg/xhr#165 Chrome will be the first browser to reject nulls in responses, despite there being wpt tests for this, so we'll have to keep an eye out for breakages. For reference, 0x00 through 0x1F aren't allowed in header values or fields, (https://tools.ietf.org/html/rfc7230#section-3.2 - VCHAR excludes those characters). CRs and LFs are of course needed, and 0x0C and 0x0B are allowed by other specs for particular header parsers, strangely. This CL does not affect other code that can generate HTTP response headers, which still uses the old behavior of just removing nulls. ServiceWorkers, extensions, WebPackages, Dial (?), and various tests still inherit the old behavior, since they create headers directly with a method that can't fail. It does introduce a new helper method, however, that they should eventually be switched to use: HttpResponseHeaders::TryToCreate(). We should probably put off conversion until this successfully makes it to stable. Bug: 832086 Change-Id: Ib75ac03a6a298238cafb41eaa5f046c082fd0bdf

While the HTTP spec further limits what values are legal, nulls are particularly concerning, and it's safest just to reject them. See discussion here: whatwg/xhr#165 Chrome will be the first browser to reject nulls in responses, despite there being wpt tests for this, so we'll have to keep an eye out for breakages. For reference, 0x00 through 0x1F aren't allowed in header values or fields, (https://tools.ietf.org/html/rfc7230#section-3.2 - VCHAR excludes those characters). CRs and LFs are of course needed, and 0x0C and 0x0B are allowed by other specs for particular header parsers, strangely. This CL does not affect other code that can generate HTTP response headers, which still uses the old behavior of just removing nulls. ServiceWorkers, extensions, WebPackages, Dial (?), and various tests still inherit the old behavior, since they create headers directly with a method that can't fail. It does introduce a new helper method, however, that they should eventually be switched to use: HttpResponseHeaders::TryToCreate(). We should probably put off conversion until this successfully makes it to stable. Bug: 832086 Change-Id: Ib75ac03a6a298238cafb41eaa5f046c082fd0bdf Reviewed-on: https://chromium-review.googlesource.com/c/1291812 Reviewed-by: Asanka Herath <[email protected]> Commit-Queue: Matt Menke <[email protected]> Cr-Commit-Position: refs/heads/master@{#601776}

…lls in them., a=testonly Automatic update from web-platform-testsHttpStreamParser: Reject headers with nulls in them. While the HTTP spec further limits what values are legal, nulls are particularly concerning, and it's safest just to reject them. See discussion here: whatwg/xhr#165 Chrome will be the first browser to reject nulls in responses, despite there being wpt tests for this, so we'll have to keep an eye out for breakages. For reference, 0x00 through 0x1F aren't allowed in header values or fields, (https://tools.ietf.org/html/rfc7230#section-3.2 - VCHAR excludes those characters). CRs and LFs are of course needed, and 0x0C and 0x0B are allowed by other specs for particular header parsers, strangely. This CL does not affect other code that can generate HTTP response headers, which still uses the old behavior of just removing nulls. ServiceWorkers, extensions, WebPackages, Dial (?), and various tests still inherit the old behavior, since they create headers directly with a method that can't fail. It does introduce a new helper method, however, that they should eventually be switched to use: HttpResponseHeaders::TryToCreate(). We should probably put off conversion until this successfully makes it to stable. Bug: 832086 Change-Id: Ib75ac03a6a298238cafb41eaa5f046c082fd0bdf Reviewed-on: https://chromium-review.googlesource.com/c/1291812 Reviewed-by: Asanka Herath <[email protected]> Commit-Queue: Matt Menke <[email protected]> Cr-Commit-Position: refs/heads/master@{#601776} -- wpt-commits: 89637ce97bb8073a2db5182fc100125acba01481 wpt-pr: 13663

…ntaining 0x00, a=testonly Automatic update from web-platform-testsFetch/XHR: response header value containing 0x00 As discussed in whatwg/xhr#165 these should turn the response into a network error. -- wpt-commits: 3d172bc612e03a896b5611d9e9652f860995feef wpt-pr: 10424 UltraBlame original commit: 0d71b9cb47cea8e9ace98cbffa1585cd9c97c8ca

…lls in them., a=testonly Automatic update from web-platform-testsHttpStreamParser: Reject headers with nulls in them. While the HTTP spec further limits what values are legal, nulls are particularly concerning, and it's safest just to reject them. See discussion here: whatwg/xhr#165 Chrome will be the first browser to reject nulls in responses, despite there being wpt tests for this, so we'll have to keep an eye out for breakages. For reference, 0x00 through 0x1F aren't allowed in header values or fields, (https://tools.ietf.org/html/rfc7230#section-3.2 - VCHAR excludes those characters). CRs and LFs are of course needed, and 0x0C and 0x0B are allowed by other specs for particular header parsers, strangely. This CL does not affect other code that can generate HTTP response headers, which still uses the old behavior of just removing nulls. ServiceWorkers, extensions, WebPackages, Dial (?), and various tests still inherit the old behavior, since they create headers directly with a method that can't fail. It does introduce a new helper method, however, that they should eventually be switched to use: HttpResponseHeaders::TryToCreate(). We should probably put off conversion until this successfully makes it to stable. Bug: 832086 Change-Id: Ib75ac03a6a298238cafb41eaa5f046c082fd0bdf Reviewed-on: https://chromium-review.googlesource.com/c/1291812 Reviewed-by: Asanka Herath <asankachromium.org> Commit-Queue: Matt Menke <mmenkechromium.org> Cr-Commit-Position: refs/heads/master{#601776} -- wpt-commits: 89637ce97bb8073a2db5182fc100125acba01481 wpt-pr: 13663 UltraBlame original commit: 8fc01167cf39bf970ad99953b0776f4338ddca84

annevk added a commit to web-platform-tests/wpt that referenced this issue Apr 11, 2018

XMLHttpRequest: response header value containing 0x00

74c1042

As discussed in whatwg/xhr#165 these should turn the response into a network error.

annevk mentioned this issue Apr 11, 2018

XMLHttpRequest: response header value containing 0x00 web-platform-tests/wpt#10424

Merged

annevk mentioned this issue Jun 20, 2018

field-value rule does not allow single field-vchar surrounded by whitespace [was: fix field-value ABNF] httpwg/http-core#19

Closed

annevk added a commit to web-platform-tests/wpt that referenced this issue Aug 28, 2018

Fetch/XHR: response header value containing 0x00

3d172bc

As discussed in whatwg/xhr#165 these should turn the response into a network error.

annevk mentioned this issue Oct 19, 2018

Fetch: test nosniff parsing better web-platform-tests/wpt#13559

Merged

chromium-wpt-export-bot mentioned this issue Oct 22, 2018

HttpStreamParser: Reject headers with nulls in them. web-platform-tests/wpt#13663

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CYBAI mentioned this issue May 9, 2020

WPT cookies/http_state tests are slow servo/servo#25606

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annevk mentioned this issue Aug 21, 2020

Coop header parsing null byte web-platform-tests/wpt#25181

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rfc6265bis UA requirements and WPT mismatch httpwg/http-extensions#1136

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HTTP/1 parsing whatwg/fetch#1156

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Test control characters in Set-Cookie header values web-platform-tests/wpt#28290

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Define what consequences NULL bytes (0x00) or other invalid values in header names have whatwg/fetch#1747

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Why does headers-normalize-response.htm expect null bytes to be allowed? #165

Why does headers-normalize-response.htm expect null bytes to be allowed? #165

wisniewskit commented Oct 16, 2017

annevk commented Oct 16, 2017

mnot commented Oct 19, 2017

annevk commented Oct 19, 2017

yutakahirano commented Oct 20, 2017

davidben commented Oct 20, 2017

wisniewskit commented Feb 18, 2018

annevk commented Apr 11, 2018

bencebeky commented Apr 11, 2018

annevk commented Apr 11, 2018

bencebeky commented Apr 11, 2018

annevk commented Apr 11, 2018

jakearchibald commented Apr 11, 2018

bencebeky commented Apr 11, 2018

annevk commented Apr 11, 2018

bencebeky commented Apr 11, 2018

annevk commented Apr 11, 2018

bencebeky commented Apr 11, 2018

annevk commented Apr 11, 2018

MattMenke2 commented Apr 11, 2018 via email

bencebeky commented Apr 12, 2018

annevk commented Aug 28, 2018

Why does headers-normalize-response.htm expect null bytes to be allowed? #165

Why does headers-normalize-response.htm expect null bytes to be allowed? #165

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wisniewskit commented Oct 16, 2017

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