Cookies leaking temporarily #74

Prerequisites

• I performed a cursory search of the issue tracker to avoid opening a duplicate issue
  • Your issue may already be reported.
  • I also searched the existing issues at https://github.com/gorhill/uMatrix/issues
• This is not a support issue or a question
  • Support issues and questions are handled at /r/uMatrix
• I tried to reproduce the issue when...
  • uMatrix is the only extension
  • uMatrix with default lists/settings
  • using a new, unmodified browser profile
• I am running the latest version of uMatrix
• I checked the documentation to understand that the issue I report is not a normal behavior
• I used the logger to rule out that the issue is caused by my ruleset

Description

It used to be the case until a week (a few weeks ago?) that if you tried to log into any website with cookies blocked globally, you wouldn't be able to until you manually allowed them for the site (true for both normal and incognito windows). Now it is possible to log into most, if not all, websites for a couple of minutes until you get the notice that you're not logged in. Furthermore, you are able to stay logged in for what seems indefinitely using an Incognito window (which didn't use to be the case).

My understanding was that uMatrix allowed the cookies into the browser but not out of it. So, now somehow websites are allowed to read this cookies.

A specific URL where the issue occurs

Any page that requires a login, e.g. github.com.

Steps to Reproduce

On a regular tab:

1. Visit github.com and enter your details.
2. Login succesfully and do some stuff.
3. Wait a few minutes and voila you're disconnected.

On Incognito Mode:

1. Visit github.com and enter your details.
2. Login successfully and do some stuff.
3. Keep using the site until you manually logoff or close the window.

Supporting evidence

I don't really know which supporting evidence to post in this particular case, so the next screenshot is the best that I could think of:

This is specially weird since the logger shows the cookies as blocked.

Your environment

• uMatrix version: 1.3.14
• Browser Name and version: Google Beta 70.0.3538.67 (Official Build) beta (64-bit)
• Operating System and version: Microsoft Windows 8.1