Alarm Raised for Critical Broadcom Wi-Fi Driver Flaw

Computer security analysts are raising the alarm for a critical vulnerability in the Broadcom wireless driver embedded in PCs from HP, Dell, Gateway and eMachines.

The vulnerability, which exposed as part of the MoKB (Month of Kernel Bugs) project, is a stack-based buffer overflow in the Broadcom BCMWL5.SYS wireless device driver that could be exploited by attackers to take complete control of a Wi-Fi-enabled laptop.

The vulnerability is caused by improper handling of 802.11 probe responses containing a long SSID field and can lead to arbitrary kernel-mode code execution.

The volunteer ZERT (Zero Day Emergency Response Team) warns that the flaw could be exploited wirelessly if a vulnerable machine is within range of the attacker.

Read more here about the demo of the Wi-Fi hack at the Black Hat conference.

"If you are near other users with laptops, you are at risk. If you are at an airport, coffee shop, or using your computer with the wireless card enabled in any public place, you are at risk. It is remote by the means of RF transmissions, the distance is dependent on the attackers antenna and signal strength," the group warned in an advisory issued jointly with H.D. Moores Metasploit project, the SANS ISC (Internet Storm Center), and Beyond Securitys SecuriTeam.

Microsofts Windows operating system is exploitable without the existence of an access point or any interaction from the user.

"The cards background scan of available wireless networks triggers the flaw," the group said.

The bug was first discovered by wireless security guru Jon "Johnny Cache" Ellch, the researcher who was embroiled in a controversy with Apple over similar bugs in the Wi-Fi driver that ships with the Mac OS X.

Ellch gave a public demonstration of the flaw at Microsofts Blue Hat hacker summit in October 2006.

Ellch reported the bug to Broadcom earlier in 2006 and waited until the company issued its patch before going public with the details. He also collaborated with the Metasploit Project on an exploit module that is now available in the point-and-click penetration testing tool.

ZERT, a group of well-respected security professionals that offers third-party fixes for critical vulnerabilities, says its not practical to issue a patch for the Broadcom issue.

"Although most of these vendors and manufacturers use the same basic driver, it differs enough that in most cases a single patch just wont cut it. Further, building a patch for all the different drivers from each vendor and all their versions, as well as test against them, is impractical," according to the ZERT alert.

Broadcom, in Irvine, Calif., has released a fixed driver to partners, but the availability of fixes for end-users appear to be very limited.

ZERT said is only aware of a driver from Cisco Systems Linksys that specifically patches this problem.

"[The Linksys fix] may work for other Broadcom-based cards as well, but there it is hard to predict. Many vendors have released drivers that are more recent than the driver that was tested. While we cant tell if these drivers patch the problem, we still assume that its a good idea to install them," the group said.

In addition to Linksys, Zonet and several other unnamed wireless card manufactures provide devices that ship with the vulnerable Broadcom driver.

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