Windows 7: Experts Warn of New Windows Shortcut Flaw

Researchers have discovered a sophisticated new strain of malicious software that piggybacks on USB storage devices and leverages what appears to be a previously unknown security vulnerability in the way Microsoft Windows processes shortcut files.





VirusBlokAda, an anti-virus company based in Belarus, said that on June 17 its specialists found two new malware samples that were capable of infecting a fully-patched Windows 7 system if a user were to view the contents of an infected USB drive with a common file manager such as Windows Explorer.



USB-borne malware is extremely common, and most malware that propagates via USB and other removable drives traditionally has taken advantage of the Windows Autorun or Autoplay feature. But according to VirusBlokAda, this strain of malware leverages a vulnerability in the method Windows uses for handling shortcut files.

Reports have been circulating for a few weeks about a new attack being targeted at certain Windows users that used USB memory sticks to propagate. More details have now emerged, including confirmation from Microsoft that a new flaw exists and is being exploited.

The attack uses specially crafted shortcut (.lnk) files, which trick Windows into running code of an attacker's choosing. Any Windows application that tries to display the shortcut's icon—including Explorer—will cause exploitation, so even the mere act of browsing a directory with the malicious shortcuts is sufficient for a system to be exploited. Analysis suggests that the shortcuts are not improperly formed; rather they depend on a flaw in the way that Windows handles shortcuts to Control Panel icons.

The first reports of the problem came last month from Belorussian security company VirusBlokAda. The company found systems infected with the flaw through infected USB keys. The keys use the flaw to install a rootkit to hide the shortcuts, dubbed Stuxnet, including kernel-mode drivers, and a malicious payload. The rootkit is itself noteworthy: the drivers it installs are signed. The certificate used to sign them belongs to Realtek, suggesting that somehow the attackers have access to Realtek's private key. The certificate used to sign the rootkit has now been revoked by Verisign.

Microsoft is looking into a particularly nasty family of malware, which has been labeled 'Stuxnet' by security researchers, and has been seen in the wild in India, Iran, the US and Indonesia, Microsoft said in a blog post on Friday. One of the attack vectors Stuxnet uses is via USB stick. The malware requires no user interaction to infect the system. The operating system merely rendering an icon launches the malware.

What amazes me more is still the amount of people that get infected with Viruses and Malware.