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Date: Tue, 01 Apr 2014 11:46:40 -0700
From: Eric Rand <eric.rand@...wnhatsecurity.com>
To: fulldisclosure@...lists.org
Subject: Re: [FD] Access anyone's Facebook "profile picture" in full
 resolution regardless of the ACL restriction

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Security through obscurity is not security at all; if you are going to
provide ACLs, then you have an ethical obligation to ensure that they
do work regardless of the access path of the file.

Compromising a facebook account and 'leaking' the image URLs for
access by other persons provides a means of obscuring the path of
leakage, thus compromising the capability of auditing the source of
the breach.

In cases where the breach violates the law, as per California's
statutes against 'revenge porn' and the like, this directly inhibits
the ability of police to investigate the breach.

Accordingly, just as in the case of the AT&T "breach", Facebook is
keeping data in a publicly accessible fashion that should not be
publicly accessible.

The best practices for these situations is to enforce ACLs by
authenticating those users requesting a file to ensure that they are
permitted to do so, instead of relying on knowledge of the URL as the
authorization token.

On 04/01/2014 07:49 AM, Philip Whitehouse wrote:
> Again they need the URL.
> 
> If you have a way to determine the URL of a specific user's profile
> image from public info that would be a vulnerability.
> 
> Simply the ability for a user or allowed visitor to copy the URL is
> not.
> 
> You can determine who can see the URL in your Facebook privacy
> settings.
> 
> Philip Whitehouse
> 
> ----- Reply message ----- From: "Bipin Gautam"
> <bipin.gautam@...il.com> To: "Philip Whitehouse"
> <philip@...uk.com> Cc: "fulldisclosure"
> <fulldisclosure@...lists.org> Subject: Access anyone's Facebook
> "profile picture" in full resolution regardless of the ACL
> restriction Date: Tue, Apr 1, 2014 15:19
> 
> Hi,
> 
> the POC is about "anyone being able to access anyone's facebook 
> profile picture in full resolution" + regardless of the ACL set to 
> their facebook profile picture (say; even when your profile
> picture permission of your facebook is set as... viewable to "only
> me" or "friends" ) ...anyone can see your full resolution profile
> picture even without logging on to facebook with the following
> method!
> 
> (Assumption: maybe if you (your ISP?) are using CDN and someone in 
> your ISP / region have already viewed the profile picture and as it
> is already fetched locally / cached in local CDN so, other party
> can access it? Does CND have IP restriction for a region / ISP ? )
> 
> Try... it works for me, Make sense ?
> 
> 
> On 4/1/14, Philip Whitehouse <philip@...uk.com> wrote:
>> This is not a vulnerability.
>> 
>> The image path is not predictable. Sharing the URL is by itself
>> giving permission for the other party to see it.
>> 
>> Even if it were possible to restrict access it could be
>> circumvented by downloading it and emailing the file instead of
>> the URL
>> 
>> 
>> Philip Whitehouse
>> 
>> ----- Reply message ----- From: "Bipin Gautam"
>> <bipin.gautam@...il.com> To: "fulldisclosure"
>> <fulldisclosure@...lists.org> Subject: Access anyone's Facebook
>> "profile picture" in full resolution regardless of the ACL
>> restriction Date: Tue, Apr 1, 2014 10:59
>> 
>> Hi List,
>> 
>> I felt like writing / pointing this minor issue, as it as its
>> "Facebook" ...
>> 
>> This issue is due to the way facebook pictures are stored in CDN 
>> without authentication mechanism, during accessing it. (which
>> would be way technically complicated to implement it)
>> 
>> Also, it is a Facebook feature that... if you have full path of
>> an image, you can pass it to anyone over the internet which they
>> can access it directly (and the facebook user should not have
>> unrealistic expectation to privacy. Hence, if someone can access
>> an image they can save/email it to others, anyway.)
>> 
>> 
>> POC:
>> 
>> ( Please TEST it in a real profile, real world example and it
>> should work. I obviously changed the URL, POC below, to
>> gibberish "6549_16544614736_444444875_n.jpg" )
>> 
>> STEPS:
>> 
>> You could try this by :
>> 
>> - changing your own facebook profile picture viewable to "only
>> me", then bookmark your own Facebook profile and logout and clear
>> cache.
>> 
>> - or then try different browser with your own profile from
>> bookmark, without logging in to facebook!
>> 
>> - or pass your FB profile to a friend, with the following
>> instruction.
>> 
>> ___
>> 
>> - then, in your browser, "Right click the Facebook profile image"
>> that you want to access in full resolution (that have ACL as
>> access to "only me" or "friends" ) > click "Copy image location"
>> > paste it in notepad
>> 
>> sample url you will get (this link below is broken)
>> 
>> :[1] 
>> https://fbcdn-profile-a.akamaihd.net/hprofile-ak-frc3/t1.0-1/c0.18.160.160/p160x160/6549_16544614736_444444875_n.jpg
>>
>>
>>
>> 
to remove from [1]: "/c0.18.160.160/p160x160"   (part; in other cases,
>> the url structure may be different, you just have to find and
>> remove this middle part...)
>> 
>> final modified url from above, which you can access the profile 
>> picture in full resolution via your browser :
>> 
>> https://fbcdn-profile-a.akamaihd.net/hprofile-ak-frc3/t1.0-1/6549_16544614736_444444875_n.jpg
>>
>>
>>
>> 
Respectfully,
>> -bipin
> 
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