Simon Willison’s Weblog

Side-channel attacking browsers through CSS3 features. Really clever attack. Sites like Facebook offer iframe widgets which show the user’s name, but due to the cross-origin resource policy cannot be introspected by the site on which they are embedded. By using CSS3 blend modes it’s possible to construct a timing attack where a stack of divs layered over the top of the iframe can be used to derive the embedded content, by taking advantage of blend modes that take different amounts of time depending on the colour of the underlying pixel. Patched in Firefox 60 and Chrome 63.

# 1st June 2018, 2:54 pm / timing-attack, sidechannel, css3, security

Side-Channel Leaks in Web Applications. Interesting new security research. SSL web connections encrypt the content but an attacker can still see the size of the HTTP requests going back and forward—which can be enough to extract significant pieces of information, especially in applications that make a lot of Ajax requests.

# 23rd March 2010, 4:24 pm / ssl, security, sidechannel, http, ajax

Side-Channel Attacks and Security Theatre. “In order to mount most of these attacks the attacker must be local [...] every good security person knows that if your attacker has the ability to run stuff on your machine, it is game over, so why are we even caring about these attacks?”

# 2nd August 2007, 12:30 pm / ben-laurie, security, sidechannel, openssl, securitytheatre