A just-published attack tactic that bypasses the security protections of most current antivirus software is a "very serious" problem, an executive at one unaffected company said today.

Last Wednesday, researchers at Matousec.com outlined how attackers could exploit the kernel driver hooks that most security software use to reroute Windows system calls through their software to check for potential malicious code before it's able to execute.
Calling the technique an "argument-switch attack," a Matousec-written paper spelled out in relatively specific terms how an attacker could swap out benign code for malicious code between the moments when the security software issues a green light and the code actually executes.

According to Matousec, nearly three-dozen Windows desktop security titles, including ones from Symantec, McAfee, Trend Micro, BitDefender, Sophos and others, can be exploited using the argument-switch tactic. Matousec said it had tested the technique on Windows XP SP3 and Vista SP1 on 32-bit machines.

Kaspersky Lab had a similar reaction. "[We] have analyzed the published material and concluded that the issue is only linked to certain features of [our] products," Kaspersky said in an e-mailed statement. "Kaspersky Lab products implement not only [kernel] hooks, but a wide range of technologies, including secure sandboxing and other methods of restricting suspicious kernel mode activity."
Huger confirmed that attackers would have to drop malware of some sort on the targeted machine in order to utilize the argument-switch strategy, and that there are "lots of easier ways to game antivirus" than Matousec's technique.
"But that doesn't lesson the impact," Huger argued. "Actually, it would be really tricky to stop this, and gives attackers a strong opportunity to get around disk-based security."

"Any malware that we detect by our antivirus will still be blocked, just like it always was," said F-Secure's Hypponen. "So the issue only affects new, unknown malware that we do not yet have a detection signature for."

Huger expects that attacks using argument-switch will target 32-bit Windows XP machines, both because that operating system continues to dominate the Windows ecosystem, and because it lacks the PatchGuard kernel protection that Microsoft added to 64-bit versions of XP in 2005, then later to 64-bit editions of Vista and Windows 7 .
"They may not be exclusive to Windows XP, but they'll be more prevalent under XP," Huger said.
Microsoft faced resistance from several antivirus companies, notably Symantec and McAfee, before the release of Windows Vista. They complained that PatchGuard would prevent them from delivering key functions in their Vista-compatible products, including behavior-based virus detection, host-based intrusion prevention and software tamper protection. Microsoft relented and eventually made security application programming interfaces (API) available to allow vendors to do what they needed without accessing the kernel.
Those APIs first appeared in Windows Vista SP1 in 2008.
Matousec claimed that 64-bit versions of Windows boasting PatchGuard could be vulnerable in some instances. "[This] will work against all user mode hooks and it will also work against the kernel mode hooks if they are installed, for example, after disabling PatchGuard," Matousec's paper stated.

Microsoft did not immediately reply to a request for comment on Matousec's claim.
Other problems security vendors face in blocking argument-switch attacks could arise if or when they release updates, argued Huger. "Kernel driver programming is pretty tricky," he said. "Redeployment [of updates] will complicate things. Any vendor nervy enough to put out new kernel drivers will have to do a pretty significant gut check. If something goes wrong, millions of machines could be blue-screened."

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