Given the importance of privacy self-help—that is, setting your browser to control what it reveals about you when you surf the Web—I was concerned to hear that Google, among others, had circumvented third-party cookie blocking that is a default setting of Apple’s Safari browser. Jonathan Mayer of Stanford’s Center for Internet and Society published a thorough and highly technical explanation of the problem on Thursday.
The story starts with a flaw in Safari’s cookie blocking. Mayer notes Safari’s treatment of third-party cookies:
Reading Cookies Safari allows third-party domains to read cookies.
Modifying Cookies If an HTTP request to a third-party domain includes a cookie, Safari allows the response to write cookies.
Form Submission If an HTTP request to a third-party domain is caused by the submission of an HTML form, Safari allows the response to write cookies. This component of the policy was removed from WebKit, the open source browser behind Safari, seven months ago by Google engineers. Their rationale is not public; the bug is marked as a security problem. The change has not yet landed in Safari.
Mayer says Google was exploiting this yet-to-be-closed loophole to install third-party cookies, the domain of which Safari would then allow to write cookies. After describing “(relatively) straightforward” cookie synching, Mayer says:
But we noticed a special response at the last step for Safari browsers. … Instead of responding with the “_drt_” cookie, the server sends back a page that includes a form and JavaScript to submit the form (using POST) to its own URL.
Third-party cookie blocking evaded, and users’ preferences frustrated.
Ars Technica has published Google’s response, which doesn’t seem to have gone up on any of its blogs, in full. Google says they created this functionality to deliver better services to their users, but doing so inadvertently allowed Google advertising cookies to be set on the browser.
I don’t know that I’m technically sophisticated enough to register a firm judgement, but it looks to me like Google was faced with an interesting dilemma: They had visitors who were signed in to their service and who had opted to see personalized ads and other content, such as ‘+1’s but those same visitors had set their browsers contrary to those desires. Google chose the route better for Google, defeating the browser-set preferences. That, I think, was a mistake.
I wonder if there isn’t some Occam’s Razor that a Google engineer might have applied at some point in this process, thinking, “Golly, we are really going to great lengths to get around a browser setting. Are we sure we should be doing this?” Maybe it would have been more straightforward to highlight to Safari users that their settings were reducing their enjoyment of Google’s services and ads, and to invite those users to change their settings. This, and urging Apple to fix the browser, would have been more consistent with the company’s credo of non-evil.
Now, to the ideological stuff, of which I can think of two items:
1) There is a battle for control of earth out there—well, a battle over whether third-party cookie blocking is good or bad. Have your way advocates. I think the consuming public—that is, the market—should decide.
2) There is a battle to make a federal case out of every privacy transgression. An advocacy group called Consumer Watchdog (which has been prone to privacy buffoonery in the past) hustled out a complaint to the Federal Trade Commission. I think the injured parties should be compensated in full for their loss and suffering, of which there wasn’t any. De minimis non curat lex, so this is actually just a learning opportunity for Google, for browser authors, and for the public.
Kudos and thanks are due to Jonathan Mayer, as well as ★★★★★ and Ashkan Soltani, for exposing this issue.
As noted 
The Technology Liberation Front is the tech policy blog dedicated to keeping politicians' hands off the 'net and everything else related to technology.