SEC Consult SA-20170403-0 :: Misbehavior of PHP fsockopen function Apr 03 2017 08:40AM
SEC Consult Vulnerability Lab (research sec-consult com)
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
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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("", 80);

// This request will go to port 53
fsockopen("", 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)
2017-03-07: Changes were committed to the PHP's main repo in Github.

2017-04-03: Public disclosure of the advisory


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

Advisory URL:


SEC Consult Vulnerability Lab

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

About SEC Consult Vulnerability Lab
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recommendation about the risk profile of new technologies.

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EOF Fikri Fadzil / @2017

Version: GnuPG v2


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