IP Source

Saturday, 11 February 2012

Firesheep and Sidejacking

The recent release of the Firesheep Wi-Fi attack tool has increased awareness among both users and attackers of the inherent insecurity of unprotected HTTP connections. Users on unprotected networks who connect to web sites through plain HTTP connections expose their connections to those sites to open surveillance and full compromise.

Firesheep allows an attacker connected to the local network to monitor the web sessions of other users on that network. The attacker can then also commandeer the sessions of others, acting in their user context. Firesheep specifically targets open Wi-Fi networks, but the problem is the same on conventional wired Ethernet networks.

None of this is new. These problems have been generally known, at least in the security community, for years. Firesheep has opened the vulnerability up to others and put devastating identity theft attacks in easy reach of even casual hackers. As experts proclaimed in reaction to Firesheep, the best solution to the problem is to use TLS/SSL for all connections to web sites, including the home page. Perhaps owing to the increased need for processing power it would entail, many large sites have been sparing in their use of TLS/SSL, but such frugality is increasingly indefensible in the face of the level of threats and true costs.


802.11 wireless networking has a troubled history with respect to security. The earliest security mechanism, WEP or Wired Equivalent Privacy, was always difficult to use and eventually turned out to be fatally flawed. Any WEP implementation can be hacked easily with free tools. Mostly because of the ease of use problems, it became very popular to leave Wi-Fi access points wide open with no encryption or authentication at all. Even though effective and easy-to-use protection, in the form of WPA2 (Wi-Fi Protected Access version 2), is now ubiquitous, open Wi-Fi is still quite common, even for installations which appear to be secure.

For instance, users typically access public Wi-Fi networks by connecting to the local network and then authenticating for full Internet access on a web page served by a local router. The data may be encrypted from the router to the rest of the Internet (although it probably is not), but the local network in and around the coffee shop is still wide open and unencrypted. As a result, any traffic from the clients there to the Internet is unencrypted. The only comprehensive way for users to protect themselves on such a network is to use a virtual private network.
Most of the traffic on public Wi-Fi networks (and many private ones as well) is HTTP, originally the application protocol of the Web, but widely used for many applications. Unless the local and server applications have implemented some sort of private encryption protocol, which is atypical, HTTP is unencrypted. All traffic is in plain text on the local network and anyone on that same network can read it.

The problem is exacerbated by common practices of web sites with cookies. HTTP is stateless and sessionless, which means that individual HTTP commands are independent and unconnected by the server itself. It is up to applications running on the server to keep track of users and their session data, such as the document they are viewing and what they’re doing with it.
The standard way to keep track of such things is with cookies, which are data stored locally by the client and associated with a particular server or domain. The server sends these cookies to the client and they are sent back unchanged by the client to the server. The cookies can contain sensitive personal data or other identifying information which can be used by the server to identify the client. Cookies which are used specifically to track user sessions are called session cookies.
Cookies can be sent with a "secure" flag which tells the browser only to send it over an HTTPS (TLS/SSL) session. It is common for web sites to encrypt the login process, but not use the secure flag for session cookies. An attacker monitoring an open network can see not only the data sent between the server and client, but also the data in the unsecured cookies. The cookie data then can be used to spoof the user with an attack technique known as sidejacking, which is one form of session hijacking. This is what Firesheep does.

Firesheep is an extension for the Firefox web browser developed by Eric Butler and released in October, 2010 at ToorCon 12, a hacker conference in San Diego. It uses a packet sniffer to intercept unsecured cookies. It displays the names of users on the local network and the services to which they are connected. The attacker can connect to those services using the victim user’s credentials by double-clicking on the name.


An intelligent, resourceful, and motivated user could protect themselves against such threats. After Firesheep was revealed, numerous technical options were presented, none of which are accessible to lay users or provide good protection by default. One was a Firefox add-in from the Electronic Frontier Foundation called HTTPS Everywhere. This program turns HTTP requests from the browser into HTTPS requests. This works—sort of—with sites which have SSL available but default to HTTP.

As the HTTPS Everywhere page itself explains, it has some problems. For example, it only works with the Firefox browser, it prevents connections to some wireless networks, and users lose access to many Google services. But even if a user is happy with this configuration, it is still possible that the site will use JavaScript to transmit cookies in plain-text HTTP.

Where open Wi-Fi networks are concerned, it would be a lot more secure simply to implement WPA2 with a shared password and put a sign up that says "The password is xxxxxxx’ or to make the network name ‘coffeehouse pw is xxxxxxx’. This would allow anyone to get on the network, just as with an open network, but WPA2 also implements user isolation so no packet sniffing would be possible. Unfortunately, web sites can’t count on open network administrators to do this.

A better solution is a virtual private network (VPN), which provides an encrypted tunnel from the client system to the some other point on the Internet from which all client communications are proxied. While there are consumer VPNs available, they are not well-known, are difficult to use, and can degrade performance, especially on latency-sensitive applications like VOIP and video.
But none of these solutions can possibly be adequate because they require users to take affirmative measures to protect themselves. No matter how much you educate them about it, many users will fail to take these measures and then still be surprised when they are compromised.

Until recently, because of its popularity, Facebook was the most prominent example of the problem of unsecured web sites. In late January, 2011 the company announced an option for users to to turn on HTTPS for all Facebook traffic, but they did not make HTTPS the default though, and few users will turn the option on. It is possible that Facebook is viewing this as a test period and that they will eventually make HTTPS the rule site wide.

Sites which use TLS/SSL site wide are immune to sidejacking. TLS/SSL is, in fact, the only good solution to the problem. Eric Butler himself puts it this way: "The only effective fix for this problem is full end-to-end encryption, known on the web as HTTPS or SSL." Full use of TLS/SSL means full use of the secure flag for cookies. For all practical purposes, all attacks based on packet sniffing fail against a site protected in this way. Sites that commit to use TLS/SSL for the safety of their users then also need to use a trusted Certificate Authority. Full HTTPS authentication with a trusted CA is the only way for users to know for sure who they are dealing with. Note that Facebook’s new SSL feature is a user option and therefore can only be applied after the user has logged in. Since Facebook does not use SSL by default for their home page, users are not completely protected from home page spoofing or eavesdropping.