[gaia e-mail] sanitizing web-bug images?

Andrew Sutherland asutherland at asutherland.org
Thu Aug 16 02:22:11 UTC 2012


On 08/15/2012 06:40 PM, Ehsan Akhgari wrote:
> By visibility, do you mean visibility as perceived by humans or 
> visibility as perceived by layout engines (determined by whether an 
> element consumes a big enough box in the rendering)?  Would the 
> sanitization algorithm be able to detect the following test cases as 
> web bugs?
>
> <img width=100 height=20 src=http://evil.com/webbug-transparent-1x1.png>
>
> <img width=100 height=20 
> src=http://evil.com/webbug-whiteorsameasbgcolor-100x20.png>

I mainly meant that if they are going out of their way to make something 
hidden as setting explicit width/height does, or positioning the actual 
image offscreen, that can be known statically.  If they don't set 
explicit width/height for an actual 1x1 image, there's no psychic 
heuristic that can tell us that in order to prevent loading the image.

We could, of course, have an analytical pass that runs on the images 
after they are loaded and feeds that information forward to subsequent 
e-mails from that sender or linking to that domain.  But that's more of 
the arms war thing.


I may have given the impression that I'm trying to fight the privacy 
battle more than I am.  Trying to distil the issue further, I think my 
question is perhaps:

It's clear that 1x1 images are just web-bugs that are wasted network 
traffic and a waste of screen real estate to prompt for.  Is it worth 
the immediate UX and network benefit now of just nuking these with the 
knowledge that this could result in those senders making things worse 
for the user by simply including a larger graphic as a web bug?

Note: It also could make things slightly better if they just use all of 
the other images they link to as web-bugs instead.

The answer to the slightly different question of whether it's a good 
idea to fight tracking when the user reads an email is that it's not a 
good idea and an arms war is expected to ensue, at least if adopted at a 
wide scale.  And then I might presume the answer is that nuking the 
1x1's (if adopted at a wide-scale) is also most likely to just cause 
explicit 1x1's to disappear, thereby increasing network traffic because 
it's more likely for people to use larger tracker images than improve 
their image serving apparatus that is used for the non-tracking bit of 
the e-mail.


> If not, I don't think this battle is worth fighting.  :/

If we were going to fight the privacy battle, it would probably best be 
fought by porting collusion to/writing something similar for 
Thunderbird, possibly with a more heuristic driven approach.  So the 
infobar could say "This e-mail contains an image that only seems to 
exist to track when you read the e-mail." or "The image links in this 
e-mail appear to contain unique information that will let the sender 
know that you are viewing this message."

Andrew





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