Simply booting up a Wi-Fi-enabled laptop can tell people sniffing wireless network traffic a lot about your computer--and about you.
Soon after a computer powers up, it starts looking for wireless networks and network services. Even if the wireless hardware is then shut-off, a snoop may already have caught interesting data. Much more information can be plucked out of the air if the computer is connected to an access point, in particular an access point without security.
"You're leaking all kinds of information that an attacker can use," David Maynor, chief technology officer at Errata Security, said Thursday in a presentation at the Black Hat DC event here. "If the government was taking this information from you, people would be up in arms. Yet you're leaking this voluntarily using your laptop at the airport."
There are many tools that let anyone listen in on wireless network traffic. These tools can capture information such as usernames and passwords for e-mail accounts and instant message tools as well as data entered into unsecured Web sites. At the annual Defcon hacker gathering, a "wall of sheep" always lists captured log-in credentials.
Errata has developed another network sniffer that looks for traffic using 25 protocols, including those for the popular instant message clients as well as DHCP, SNMP, DNS and HTTP. This means the sniffer will capture requests for network addresses, network management tools, Web sites queries, Web traffic and more.
"You don't realize how much you're making public, so I wrote a tool that tells you," said Robert Graham, Errata's chief executive. The tool will soon be released publicly on the Black Hat Web site. Anyone with a wireless card will be able to run it, Graham said. Errata also plans to release the source code on its Web site.
The Errata sniffer, dubbed Ferret, packs more punch than other network sniffers already available, such as Ethereal and Kismet, because it looks at so many different protocols, Graham said. Some at Black Hat called it a "network sniffer on steroids."
Snoops can use the sniffer tools to see all kinds of data from wireless-equipped computers, regardless of the operating system.
For example, as a Windows computer starts up, it will emit the list of wireless networks the PC has connected to in the past, unless the user manually removed those entries from the preferred networks list in Windows. "The list can be used to determine where the laptop has been used," Graham said.
Apple Mac OS X computers will share information such as the version of the operating system through the Bonjour feature, Graham said. Bonjour is designed to let users create networks of nearby computers and devices.
Additionally, computers shortly after start-up typically broadcast the previous Internet Protocol address and details on networked drives or devices such as printers that it tries to connect to, Graham said.
"These are all bits of otherwise friendly information," Graham said. But in the hands of the wrong person, they could help attack the computer owner or network. Furthermore, the information could be useful for intelligence organizations, he said.
And that's just what the data snoops can sniff out of the air when a laptop is starting up. If the computer is then connected to a wireless network, particularly the unsecured type at hotels, airports and coffee shops, much more can be gleaned. Hackers have also cracked basic Wi-Fi security, so secured networks can't provide a security guarantee.
In general, experts advise against using wireless networks to connect to sensitive Web sites such as online banking. However, it is risky to use any online service that requires a password. The Errata team sniffed one reporter's e-mail username and password at Black Hat and displayed it during a presentation.
People who have the option of using a Virtual Private Network when connected to a wireless network should use it to establish a more secure connection, experts suggest. Also, on home routers WPA, or Wi-Fi Protected Access, offers improved security over the cracked WEP, or Wired Equivalent Privacy.
"The best solution is to be aware of the danger," Graham said. "Everyone doesn't need to work from a coffee shop."