If you have an HTC smartphone running Windows Mobile 6 or Windows Mobile 6.1, you may want to think twice before connecting to an untrusted device using Bluetooth. A vulnerability in an HTC driver installed on these phones can allow an attacker to access any file on the phone or upload malicious code using Bluetooth, a Spanish security researcher warned Tuesday.
"HTC devices running Windows Mobile 6 and Windows Mobile 6.1 are prone to a directory traversal vulnerability in the Bluetooth OBEX FTP Service," security researcher Alberto Moreno Tablado said in an e-mail exchange.
HTC handsets running Windows Mobile 5 are not affected.
For the attack to work, the targeted device must have Bluetooth enabled and file sharing over Bluetooth activated.
"This connection can be done either by standard Bluetooth pairing or taking advantage of the Bluetooth MAC spoofing attack," Moreno Tablado said, referring to a process where the attacking device attempts to convince the target that it's another device on its list of paired devices.
The directory traversal vulnerability allows an attacker to move from a phone's Bluetooth shared folder into other folders, giving them access to contact details, e-mails, pictures or other data stored on the phone. They can use this access to read files or upload software, including malicious code.
Users worried about the vulnerability should avoid pairing their phones with an untrusted handset or computer. They may also want to delete any devices that are already paired with their phones, he said.
Because the driver, obexfile.dll, is an HTC driver, only handsets from the company are affected. However, HTC is the world's largest manufacturer of Windows Mobile handsets, selling phones under its own brand as well as making phones under contract for other companies. That means millions of users are potentially vulnerable.
Moreno Tablado tested the vulnerability on a range of HTC handsets, including the Touch Diamond, Touch Pro, Touch Cruise, Touch Find, S710 and S740, among others. "It seems that HTC includes this driver, which is vulnerable, in all the devices running Windows Mobile 6 and Windows Mobile 6.1, as a part of the Bluetooth stack," he said.
Moreno Tablado first reported the vulnerability to Microsoft in January, believing the problem was rooted in the Bluetooth stack used with Windows Mobile 6. At the time, Tablado did not disclose technical details of the vulnerability, believing it was a critical flaw that would put users at risk if it was disclosed.
Microsoft responded soon after the vulnerability was reported to them, saying they had determined the issue was caused by the HTC driver. But when Moreno Tablado reported the vulnerability to HTC in February, the handset maker "showed no interest," he said.
HTC and Microsoft could not immediately be reached for comment.
"I am forced to go public with all the information because HTC showed no intention to release a security fix," Moreno Tablado said, providing a link to his blog, where he posted detailed information about the vulnerability.
"I guess that all forthcoming Windows Mobile 6.5 devices will be vulnerable too if HTC does not fix the driver," he said.