Microsoft is to issue a Windows security update to plug a long known hole in the protocol that secures websites.
Although the flaw in SSL 3.0 and TLS 1.0, the follow-on web encryption protocol to SSL, has been known for about a decade, a practical exploit only surfaced last week when a pair of researchers demonstrated what they called BEAST, for "Browser Exploit Against SSL/TLS," a hacking tool that attacks browsers and decrypts cookies, potentially giving attackers access to encrypted website log-on credentials.
Opera Software's flagship desktop browser relies on TLS 1.1, which is not vulnerable to such attacks, but others have either not made that move or as in Microsoft's case, have left TLS 1.1 support disabled by default.
Update for Windows
In a security advisory issued Monday, Microsoft said it is working on an update for Windows, but did not say what it would patch or modify, or when it would deliver the fix.
"Microsoft is currently working to develop a security update for Windows to address this vulnerability," the advisory stated. "Microsoft will release the security update once it has reached an appropriate level of quality for broad distribution."
All versions of Windows, from the 10 year old Windows XP to 2009's Windows 7, are vulnerable to BEAST attacks, Microsoft said.
Andrew Storms, director of security operations at nCircle Security, doesn't believe Microsoft will rush out an emergency update, usually called out-of-band, unless real world attacks begin circulating in large numbers.
"Until we see wide-spread attacks, I don't think there will be much pressure on them to go out-of-band," said Storms. "And remember, it's not a Microsoft problem per se. It's more systemic with the implementation of cryptography that affects a wide variety of vendors."
Internet Explorer relies on Windows' implementation of SSL and TLS, the reason why Microsoft will patch the operating system and not its browser. Windows 7 and Windows Server 2008 R2 support TLS 1.1, but the newer protocol is not enabled by default because of website compatibility issues. Relatively few of the servers that power sites use TLS 1.1.
Microsoft advised server and desktop users running those editions of Windows to switch on TLS 1.1, but warned them of possible problems if they did. It also published a pair of "Fix-it" tools that automate the process of turning on TLS 1.1.
While others have said that BEAST doesn't mean that users should panic, Microsoft acknowledged the theoretical danger even as it downplayed the practicality of attacks.
"Under certain circumstances, the attacker can decrypt the encrypted SSL traffic... [but] there are significant mitigating factors that would make the attacks difficult or impossible," said a trio of Microsoft engineers from the company's security centre.
Users can avoid attacks by closing the browser tabs for all websites before browsing to an encrypted URL, designated by "HTTPS" at the front of the address, for example to log onto Hotmail or Gmail. "[If the user then] logs out of that HTTPS session before browsing any other HTTP sites or untrusted HTTPS sites, the user will NOT be at risk for this attack," said Chengyun Chu, Jonathan Ness and Mark Wodrich of the Microsoft Security Response Centre.
Some browsers, including Google's Chrome, Mozilla's Firefox and Apple's Safari, are vulnerable to attack because they don't support the more secure encryption protocols, according to researcher Thierry Zoller.
Google, however, has modified the rough-edged 'dev' build and the more polished 'beta' of Chrome to block BEAST-style attacks, and Mozilla on Tuesday said that while Firefox relies on TLS 1.0, the browser itself is not at risk.
"The technical details of the attack require the ability to completely control the content of connections originating in the browser, which Firefox does not allow," said Mozilla.
Mozilla did confirm that the researchers responsible for BEAST "found weaknesses in Java plugins that permit this attack". To stymie those attacks, Mozilla urged users to disable Java in Firefox, and said it was "currently evaluating the feasibility of disabling Java universally in Firefox installs".
To disable Java in Firefox, users should choose 'Add-ons' from the'Tools' menu, click the 'Plugins' tab on the left, then click 'Disable' for 'Java Applet Plug-in'.
Encryption questions linger
BEAST has raised a long-held concern about website encryption, said Quentin Liu, the senior director of engineering for Symantec's authentication group, which is based on the company's acquisition of VeriSign a year ago. "In general, this vulnerability has been known for years, but [BEAST] is a very interesting proof-of-concept," Liu acknowledged. "However, it does not mean the death of SSL."
Expanding on that, Liu said that newer protocols, like TLS 1.1, which harks back half a decade, offer a proven path to stymie BEAST-style man-in-the-middle attacks. The problem is that all the parties, browser makers, operating system developers and developer tool makers, haven't gotten on the same page.
"What's needed is a thoughtful migration to TLS 1.1 and beyond, a coordinated and in-sync migration path," said Liu.
While Symantec isn't one of the players who need to sit at the migration table, Liu said the company could leverage its position as a certificate issuing authority (CA) to pull others along.
"As a leader in our industry, what we can do is get all the parties that can affect change together," said Liu. "That's something we can do to try to bring people to the table."