Critical Apache flaw 'puts over 50% of Fortune 100 at risk'

More than half of the Fortune 100 could be at risk from a security flaw affecting the Apache Struts development framework, researchers have warned.

The critical vulnerability affects all versions of Apache Struts released since 2008, and leaves any server running the widely-implemented REST communication plugin open to remote code execution.

The flaw was discovered by researchers from lgtm, an open source software engineering analytics firm. "The lgtm security team have a simple working exploit for this vulnerability which will not be published at this stage," wrote Bas Van Schaik, product manager of lgmt parent company Semmle as part of a blog post announcing the vulnerability.

"At the time of the announcement there is no suggestion that an exploit is publicly available, but it is likely that there will be one soon."

The Apache Software Foundation has patched the vulnerability in Struts version 2.5.13, and any organisations using older versions are being urged to update as a matter of some urgency.

The open source software is widely used by many companies to develop their applications, with businesses like Citigroup, Virgin Atlantic and Lockheed Martin confirmed as users. In fact, RedMonk analyst Fintan Ryan pegged the number of Fortune 100 companies using Struts-based apps at at least 65%.

"This vulnerability poses a huge risk, because the framework is typically used for designing publicly-accessible web applications," said Man Yue Mo, one of the researchers who discovered the flaw. "Struts is used in several airline booking systems as well as a number of financial institutions who use it in internet banking applications. On top of that, it is incredibly easy for an attacker to exploit this weakness: all you need is a web browser."

"This is as serious as it gets," said Semmle founder Oege de Moor. "If remote attackers are allowed to exploit the newly identified vulnerability it can critically damage thousands of enterprises.

"In the spirit of open source, we want to make sure that the community and industry are aware of these findings as we help uncover critical issues in large numbers of open-source projects. Working with Apache Struts, they were extremely responsive and immediately came up with a clear remediation path."