Google implemented its Bouncer technology in February for Google Play (formerly Android Market) to check apps submitted by Android developers for any traces of malicious code. This week at the Black Hat Conference in Las Vegas, security firm Trustwave explained how it's possible to circumvent the Google Bouncer security check.

Trustwave proved to itself that its masking technique could get past Bouncer's detection by getting a malicious app it created into Google Play earlier this year, says Nicholas Percoco, senior vice president and head of Trustwave's SpiderLabs advanced security team. "We wanted to test the bounds of what it's capable of," he says, describing how Trustwave as a registered Android developer created an app called "SMS Blocker." When downloaded to a smartphone, the app would be able to steal contacts, SMS messages and photos, and basically know anything about the device. The app could also make the phone go to arbitrary web pages or launch a denial-of-service attack. He says: "Google never flagged it."

Percoco notes that Trustwave deliberately chose an SMS blocker to be its test project against Google Bouncer because there are so many of them already on Google Play, and by pricing its SMS Blocker app high, there was little likelihood anyone would actually buy and download it (no one did). But by getting the malicious app past Bouncer for more than two weeks - Bouncer, which does repeat checks, never spotted it - Trustwave says it's making the point that sophisticated attacks are likely to evade such malware detection tools.

"As an attack, all a malware attacker has to do to get into Google Play is to bypass Bouncer," Percoco points out. Bouncer's automated detection method isn't yet sufficient to spot the kind of sophisticated masking techniques that Trustwave demonstrated at the Black Hat presentation.

Percoco adds that Trustwave reached out to share its findings with Google, which he says is "a great organisation to work with," especially Adrian Ludwig in the Google Android Security division. But Percoco says a more manual approach to testing apps on Android devices for malicious code may be needed to even start to detect what Trustwave came up with as a malware-masking technique.

Stonesoft shows off

Also focusing on evasive attacks at Black Hat this week will be Stonesoft, which is announcing a product called Evasion Prevention System. This appliance is designed to detect and block attacks that rely on what the company calls "advanced evasion techniques."

"This is to detect and prevent an advanced persistent threat," says Richard Benigno, Stonesoft senior vice president, who adds that the appliance would typically reside on the network in front of an intrusion-prevention system or next-generation firewall. APTs are generally considered to be stealth attacks aimed at compromising enterprise networks for long periods of time to gain intelligence and steal critical data. The Evasion Prevention System starts at $20,000.

Stonesoft will also make available online a free tool it calls Evader, server-based software for Linux or Unix that lets organisations test their network security to see if it can withstand advanced evasion techniques. Evader is said to launch evasion techniques against the tester's own next-generation firewall, intrusion-prevention system or unified threat management device to show how it may be possible to evade defences to deliver malicious code or exploit a weakness on a target host without detection. The tool is available for download online here.