1404748 - Privacy: Disable referers and cookies in HTTP requests from emails

Status: ASSIGNED

(Thunderbird :: Security, enhancement)

Description

[Ben Bucksch (:BenB)]

https://freedom-to-tinker.com/2017/09/28/i-never-signed-up-for-this-privacy-implications-of-email-tracking/
https://senglehardt.com/papers/pets18_email_tracking.pdf Section 6.2

The study shows that we store cookies for HTTP requests. Indeed, Thunderbird default pref network.cookie.cookieBehavior is set to 0 = Allow all cookies. We should change this to 2 = Don't store/send cookies.

The study say that we do not send referers. This may be because we don't allow mailbox:/imap: URLs are referers, which is surely reasonable. However, the default pref network.http.sendRefererHeader is set to 2 = Allow referers. We should change this to 0 = Don't send referers, to make it more bulletproof.

Positive effects:
Less possibilities to track email reads/opens by spammers. (Mostly important when the user allows remote images.)

Adverse effects:
I don't expect negative effects on email reading. Remote image viewing is already disabled by default, for the same reason of tracking protection. I don't think 

Given that this is a global pref, it would affect the RSS reader as well.
I know that almost all websites work without referers, because that's my default setting for all web browsing since many years, and I have very few problems.
I would hope that most blogs work without cookies, but I have not tested that.

Comment 1

[Ben Bucksch (:BenB)]

Attachment: Suggested fix, v1

Comment 2

[Ben Bucksch (:BenB)]

Attachment: Suugested fix, v2

Sorry, other changes slipped in.

Comment 3

[Ben Bucksch (:BenB)]

Do you think that blog fetches can live without cookies?
If not, the patch gets a lot more complex.

Comment 4

[Ben Bucksch (:BenB)]

Also, do people make comments on blog posts within Thunderbird, using TB as a browser? If so, these are likely to break with this change here.

Comment 5

[Magnus Melin [:mkmelin]]

Like Matt wrote on maildev, you need cookies for OAuth2 authentication.

Comment 6

[Mike Conley (:mconley) (:⚙️) (PTO: May 24 - June 2nd)]

Comment on attachment 8914133 [details] [diff] [review]
Suugested fix, v2

I don't think I'm the right person to review this these days (mkmelin is probably the better choice) - and, as I understand it, cookies are still required for some Thunderbird features (like oAuth), so this sounds like too general a fix.

Comment 7

[Ben Bucksch (:BenB)]

Yes, agreed.
How about this:
We disable cookies, and then whitelist google OAUTH domains.
Also, when the user adds a RSS feed with full browser view, we add that blog's domain to the whitelist.

Comment 8

[alta88]

The study actually demonstrates nothing about Tb storing a cookie for an email image/link click. Do you have a testcase that proves this?  Meaning stores a local cookie for a message retrieved via imap/pop3. Yes, there is a gecko pref that defaults to 0.

A whitelist for oauth/feeds is a nonstarter imo. This sort of thing, if it's demonstrably necessary, properly belongs in content policy (where remote content blocking is already handled).

Comment 9

[Ben Bucksch (:BenB)]

> [implement as] content policy (where remote content blocking is already handled)

That's another good option, yes.

Comment 10

[Ben Bucksch (:BenB)]

The idea here is to disable cookies for everything where they are not known to be needed.

Is there any objection to disabling referers? I know that almost all websites work without referers, because that's my default setting for all web browsing since many years, and I have very few problems.

Comment 11

[Magnus Melin [:mkmelin]]

But we're not usually sending Referer, right?

For whatever browsing or web application use there is in-product, not sending it could break applications. I recall reading a paper that basically concluded web application authors can rely on Referer being there for https traffic at least. And there are good reasons to check it...