Researchers from Google and a well-known security firm have documented serious vulnerabilities in Adobe Flash content which leave tens of thousands of websites susceptible to attacks that steal the personal details of visitors.

The security bugs reside in Flash applets, the ubiquitous building blocks for movies and graphics that animate sites across the web. Also known as SWF files, they are vulnerable to attacks in which malicious strings are injected into the legitimate code through a technique known as cross-site scripting, or XSS. Currently there are no patches for the vulnerabilities, which are found in sites operated by financial institutions, government agencies and other organizations.

The vulnerabilities are laid out in the book Hacking Exposed Web 2.0: Web 2.0 Security Secrets and Solutions. It is due to hit store shelves soon, but is already in the hands of many security professionals. The book's authors, who work for penetration testing firm iSEC Partners as well as for Google, say a web search reveals more than 500,000 vulnerable applets on major corporate, government and media sites.

"Lots of people are vulnerable, and right now there are no protections available other than to remove those SWFs and wait for the authoring tools and/or Flash player to be updated," says Alex Stamos, one of the book's authors. "In the mean time, people will have to think: 'What kind of flash am I using on my site,' and manually test for vulnerabilities."

Flash flood

That could be a mammoth task, because a half-dozen of the most popular Flash authoring programs automatically generate the buggy content. What's more, the people who crank out graphics frequently work separately from a site's security team. Removing the vulnerable content will require combing through website directories for SWF files and then testing them one by one. Updates in the Adobe software that renders SWF files in browsers are also expected, but they probably wouldn't quell the threat completely, according to Stamos.

The authors have been working since the summer with Adobe, the developer of Flash, and the United States Computer Emergency Readiness Team to coordinate a remedy. An Adobe representative said patches should be released in the next few weeks. In the meantime, end users can employ the Firefox plug-in NoScript or use other methods to block Flash on sensitive websites. Flash content creators can also utilize the data validation libraries found here, as well as follow the guidelines of this Adobe whitepaper.

A security update Adobe released this week for its Flash player doesn't fix the vulnerabilities, Stamos said.

Attack scenarios work something like this: A bank website hosts marketing graphics in the form of a vulnerable Flash applet. Attackers who trick a customer into clicking on a malicious link are able to execute the SWF file but inject malicious code variables that cause the customer's authentication cookies or login credentials to be sent to the attacker.

"There are definitely lots of people who are vulnerable," Stamos said. "Tens of thousands is very conservative. Realistically, it's probably in the hundreds (of thousands)."

Shockwave to the system

One reason for the sheer volume of vulnerable applets: SWF files generated by six of the more popular content development tools automatically contain the bugs, according to the book. Those programs include DreamWeaver, Connect, Breeze - which are sold by Adobe - and TechSmith Camtasia, InfoSoft FusionCharts and software from Autodemo.

Stamos said Adobe is likely to update its Flash Player so it does a better job of vetting code variables before executing SWF files. But he said interaction with third-party code is such a core part of the way Flash works that updates to the player would likely provide only a partial fix.

Eradicating the problem will require updates for all of the graphics authoring tools so they no longer generate buggy Flash content. Even then, security pros will have to analyze all of a website's SWF files and recompile any found to be vulnerable.

The book was authored by Rich Cannings, a senior information security engineer at Google, and Himanshu Dwivedi, Zane Lackey, Chris Clark and Stamos of iSEC. It is published by The McGraw-Hill Companies. ®