Thanks Tim, 

1. Does “saw the site” mean users actually had full or partial access to the accounts of other users, or simply were viewing a cached version of the site that appeared as if they were logged in as someone else? How many users were impacted? 

2. Does the WMF hold incident review meetings and publish reports about what steps are taken to prevent repeat incidents with the same root cause? 

On Thu, Jun 25, 2020 at 7:44 PM Tim Starling <tstarling@wikimedia.org> wrote:
Everyone on Wikimedia wikis will shortly be logged out and will have
to log back in again.

We are resetting all sessions because we believe that, due to a
configuration error, session cookies may have been sent in cacheable
responses. Some users reported that they saw the site as if they were
logged in as someone else. We believe that the number of affected
users was very small. However, we believe that resetting all sessions
is a prudent measure to ensure that the impact is limited.

There are several layers of protection against something like this
happening, and we don't yet know how all of them failed, but we have
made a configuration change which should be sufficient to prevent it
from happening again.

-- Tim Starling


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