Smartphones running Microsoft's Windows Phone operating system are vulnerable to attacks that can extract the user credentials needed to log in to sensitive corporate networks, the company warned Monday.
The vulnerability resides in a Wi-Fi authentication scheme known as PEAP-MS-CHAPv2, which Windows Phones use to access wireless networks protected by version 2 of the Wi-Fi Protected Access protocol. Cryptographic weaknesses in the Microsoft-developed technology allow attackers to recover a phone's encrypted domain credentials when it connects to a rogue access point. By exploiting vulnerabilities in the MS-CHAPv2 cryptographic protocol, the adversary could then decrypt the data.
"An attacker-controlled system could pose as a known Wi-Fi access point, causing the victim's device to automatically attempt to authenticate with the access point and in turn allowing the attacker to intercept the victim's encrypted domain credentials," the Microsoft advisory warned. "An attacker could then exploit cryptographic weaknesses in the PEAP-MS-CHAPv2 protocol to obtain the victim's domain credentials."
The advisory comes a little more than a year after researchers devised an attack against the MS-CHAPv2 cryptographic scheme that made it trivial to break the encryption used by hundreds of anonymity and security services. The attack described in Monday's advisory appears to build off that exploit by combining it with behavior in Windows Phone that causes devices to automatically associate with a rogue networks without first validating the its digital certificate. When a handset attempts the CHAPv2 authentication, the operator of the rogue network can exploit the cryptographic weaknesses to recover the username and password.
"If correct, that should mean a pretty seamless attack against wireless enterprise credentials used in most corporate environments," Moxie Marlinspike, the pseudonymously named researcher who devised last year's attack, said of the latest exploit. Researcher David Hulton also helped develop last year's attack.
Microsoft doesn't intend to issue an update to patch the hole. Instead, company officials recommend users require a certificate verifying a wireless access point before starting an authentication process from Windows Phone 8 devices. The advisory contains instructions for configuring a Windows Phone device to require a certificate verifying the trustworthiness of wireless access point. The advisory also suggests turning off Wi-Fi connectivity in smartphone when not needed. Microsoft said Monday's advisory was prompted by a public report that describes a known weakness in MS-CHAP.