Security Experts:

Working Patch for PHP Security Flaw to be Released Tuesday

On Tuesday, the PHP Group plans to release new versions of PHP in order to address the problems with a previous patch, which was intended to close a security problem. As SecurityWeek reported on Friday, the first patch released by PHP was easily bypassed.

[Update: As expected, the PHP development team released PHP 5.4.3 and PHP 5.3.13. All users are encouraged to upgrade to PHP 5.4.3 or PHP 5.3.13.]

Addressing the problems on Sunday, the PHP Group said:

“Another set of releases are planned for Tuesday, May, 8th. These releases will fix the CGI flaw and another CGI-related issue in apache_request_header (5.4 only). We apologize for the inconvenience created with these releases and the (lack of) communication around them.”

The group that discovered the bug was waiting for a patch to be published before they released any information. However, last week details were leaked to Reddit prompting the group (Eindbazen) disclose what they had discovered. The issue was severe enough that CERT issued an advisory.

“When PHP is used in a CGI-based setup (such as Apache's mod_cgid), the php-cgi receives a processed query string parameter as command line arguments which allows command-line switches, such as -s, -d or -c to be passed to the php-cgi binary, which can be exploited to disclose source code and obtain arbitrary code execution,” a CERT advisory on the flaw explains.

In short, the flaw will attackers to issue commands to servers where PHP has been compiled to run under CGI mode. This is often done for security and development reasons. It’s important to note that FastCGI configurations are not impacted by the flaw.

Until Friday morning, sites such as Sony.com and Facebook.com were said to be vulnerable to the flaw. To help webmasters and administrators see the security issue in action, TrustWave’s SpiderLabs blog has a post with detailed instructions for testing PHP installations.

The examples highlight the potential for Reverse Shell attacks, Remote Code Execution, and of course Source Code Disclosure. Anyone interested can head here to view it.

Interested in Secure Development Strategies? Join us for a live Webinar on May 23 at 1:00PM: "The Great Security Divide: How security can work better with development", presented by Coverity Founder and CTO, Andy Chou. You can register free here.

Steve Ragan is a security reporter and contributor for SecurityWeek. Prior to joining the journalism world in 2005, he spent 15 years as a freelance IT contractor focused on endpoint security and security training.