Re: [RFC] drop Request-Range header support

On 27/02/2014 6:21 p.m., Alex Rousskov wrote:
> On 02/26/2014 09:51 PM, Amos Jeffries wrote:
>> While checking the code against HTTPbis Range draft I think we have a
>> possible smuggling avenue being enabled by Squid in the form of the
>> Request-Range header.
>>
>> What I can see there in Squid is parsing Request-Range into the same
>> memory structures as Range. Each time teh header is encountered erasign
>> prior headers data. Then forwarding the results upstream under the name
>> Range.
>>
>> Only one range header is specified. Multiple is udnefined behaviour. So
>> the following request may be interpreted differently by other
>> participants seeing:
>>
>> GET / HTTP/1.1
>> Range: bytes=0-1000
>> Request-Range: bytes=257-1000
>>
>>
>> * Squid will effectively strip the Range: header and relay the
>> Request-Range value in Range: upstream.
>>
>> * agents closer to the client may be interpreting that as only Range:
>> header plus unknown header.
>>
>> Content-Range on the reply should be sorting out what is actually
>> delivered so no problems are visible. But any protection based on the
>> request could be confused or tricked into not processing the reply if it
>> was only checking based on the RFC standard Range header.
>>
>>
>> This type of crafted request will also have the same behaviour in Squid:
>>
>> GET / HTTP/1.1
>> Range: bytes=0-1000
>> Range: bytes=257-1000
>>
>>
>> The proposal(s):
>>
>> A) treating the Request-Range header as obsolete and erasing it without
>> processing?
>>
>> The only mentions I can find online are CVE-2011-3192 about a
>> Flash+Apache vulnerability meaning the header had to be blocked from
>> sending by Flash and XHR mechanisms plus documentation relating. And
>> that its a legacy header from the days of MSIE 3.0 and Nescape.
>> So it looks like a candidate for dropping some more code.
>>
>>
>> B) treating multiple Range headers as an error and dropping them all.
>
> Unless they are the same perhaps? I am worried about existing HTTP
> clients (unknown to me) sending double Ranges (for no good reason).
> There is no compelling reason to drop all Ranges if they are identical,
> I think. We can leave and honor one of them.
>
>
>> This would result in Request-Range being treasted somewhat like
>> Proxy-Connection has been for some time. Either upgraded when its alone,
>> or dropped if there is a collision.
>>
>>
>> FWIW: the specification says any proxy MAY drop Range at its choice. So
>> we are permitted to erase this traffic brokenness in either of the above
>> ways.
>
> Do you propose to hard-code actions (a) and (b)? Will some existing or
> new option control this behavior?

(A) can be hard-coded in the form of either:
  i) dropping it from the header registry + using delByName() on every
request, OR
  ii) dropping explicit mentions of it outside the header registry,
setting its field type to generic String, and adding it to the
connection-headers mask.

(B) the putRange() can detect multiples and set the range to a special
(empty header?) value that gets stripped at the end of parsing. In order
not to reject even counts of Range headers while allowing odd-counts.

I kind of favour (A), but we may end up having to do both eventually
anyway to enforce correct Range compliance.

Amos
Received on Thu Feb 27 2014 - 07:58:49 MST