SEC Consult SA-20170403-0 :: Misbehavior of PHP fsockopen function

From: SEC Consult Vulnerability Lab <research@sec-consult.com>
To: bugtraq@securityfocus.com,fulldisclosure@seclists.org
Cc:
Subject: SEC Consult SA-20170403-0 :: Misbehavior of PHP fsockopen function
Date:


SEC Consult Vulnerability Lab Security Advisory < 20170403-0 >
=======================================================================
              title: Misbehavior of the "fsockopen" function
            product: PHP
 vulnerable version: 7.1.2
      fixed version:
         CVE number: CVE-2017-7272
             impact: Medium
           homepage: http://www.php.net/
              found: 2017-03-06
                 by: Fikri Fadzil (Office Kuala Lumpur)
                     SEC Consult Vulnerability Lab

                     An integrated part of SEC Consult
                     Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
                     Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich

                     https://www.sec-consult.com

=======================================================================

Vendor description:
-------------------
"PHP is a popular general-purpose scripting language that is especially suited
to web development. Fast, flexible and pragmatic, PHP powers everything from
your blog to the most popular websites in the world."

Source: http://www.php.net/


Business recommendation:
------------------------
By making use of this issue, it is possible for an attacker to bypass current
prevention mechanisms used to protect the "fsockopen" function in PHP to perform
server-side request forgery attacks.

SEC Consult recommends to check the developed or installed websites for any
possibility to exploit any form of vulnerability due to this issue.


Vulnerability overview/description:
-----------------------------------
The "fsockopen" function in PHP will respond differently if two port numbers
are given at once. As many developers assume the function will prioritize the
port number given to the second function parameter, an attacker may utilize this
unpredictable behavior to e.g. conduct a server-side request forgery attack.


Proof of concept:
-----------------
The "fsockopen" function in PHP will not use the port number given to the
second parameter if the hostname already has a port number appended. The
example below should explain misbehavior of the function.

// This request will go to port 80
fsockopen("192.168.184.132", 80);

// This request will go to port 53
fsockopen("192.168.184.132:53", 80);

Instead of initiating a socket connection on port 80 as given in the second
parameter, the function appears to use the port number 53 which is
appended to the hostname.



Vulnerable / tested versions:
-----------------------------
PHP version 7.0.11 and 7.1.2 have been tested and found to be vulnerable.

Older PHP versions are potentially affected as well.


Vendor contact timeline:
------------------------
2017-03-07: Reported the issue through PHP Bug Tracking System. (SecBug #74216)
            https://bugs.php.net/bug.php?id=74216
2017-03-07: Changes were committed to the PHP's main repo in Github.

https://github.com/php/php-src/commit/bab0b99f376dac9170ac81382a5ed526938d595a
2017-04-03: Public disclosure of the advisory


Solution:
---------
Patch:
https://github.com/php/php-src/commit/bab0b99f376dac9170ac81382a5ed526938d595a


Workaround:
-----------
It is recommended to restrict user input data for a hostname to not have a
port number appended.


Advisory URL:
-------------
https://www.sec-consult.com/en/Vulnerability-Lab/Advisories.htm


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab

SEC Consult
Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

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EOF Fikri Fadzil / @2017





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