Security researchers discovered a haunting technique that they’re calling a GhostHook attack, which uses a feature in Intel central processing units (CPUs) to take over 64-bit Windows systems. Windows has traditionally been safe from most cybercriminals trying to install rootkits, but the GhostHook attack can bypass PatchGuard, which was specifically developed to protect its operating system at the kernel level.
Experts at CyberArk described how Intel Processor Trace (IPT), which captures information about software on a PC to deal with debugging and other issues, could open a way to hook rootkits onto Windows. This would be very difficult to detect, hence the “ghost” moniker.
Hooking is not always used for malicious purposes, Dark Reading noted, and fraudsters would need to already have malware present on the system to exploit a rootkit. The GhostHook attack is particularly scary, however, because it’s happening on the kernel level. That means it’s impervious to many security products, including personal firewalls and even intrusion prevention systems (IPS).
GhostHook Attack Degrades Defenses
PatchGuard isn’t effective here. As Bleeping Computer explained, CyberArk researchers were able to allocate extremely small buffers to packets of code in IPT. Eventually, the CPU needs additional space and attempts to deal with the code by opening a performance monitoring interrupt (PMI) handler.
The GhostHook attack is extremely clever because PatchGuard wasn’t designed to look at what happens within PMI handlers. That’s also why it’s possible to plant a rootkit as the system is being patched.
Although there haven’t been any public accounts of cybercriminal activity using the GhostHook attack, a CyberArk researcher told iTWire that Windows admins should be on guard. If used in combination with disk-wiping malware, for instance, cybercriminals could do a lot of damage before they’ve ever discovered by authorities.
The Industry Responds
Microsoft has been informed about the GhostHook attack. According to CyberArk, however, the software giant said the flaw likely would not be addressed, except possibly in a future version of Windows.
It’s also possible that Intel will make it more difficult to pursue the technique in its next generation of IPT technology. Since attackers would need to have malware on the PC already, this is not yet a full-blown emergency — more like a phantom menace.