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Clarify security note regarding the domain Synapse is hosted on. (#9221)

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Denis Kasak 2021-05-27 11:41:16 +00:00 committed by GitHub
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README.rst
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@ -149,21 +149,45 @@ For details on having Synapse manage your federation TLS certificates
automatically, please see `<docs/ACME.md>`_.
Security Note
Security note
=============
Matrix serves raw user generated data in some APIs - specifically the `content
repository endpoints <https://matrix.org/docs/spec/client_server/latest.html#get-matrix-media-r0-download-servername-mediaid>`_.
Matrix serves raw, user-supplied data in some APIs -- specifically the `content
repository endpoints`_.
Whilst we have tried to mitigate against possible XSS attacks (e.g.
https://github.com/matrix-org/synapse/pull/1021) we recommend running
matrix homeservers on a dedicated domain name, to limit any malicious user generated
content served to web browsers a matrix API from being able to attack webapps hosted
on the same domain. This is particularly true of sharing a matrix webclient and
server on the same domain.
.. _content repository endpoints: https://matrix.org/docs/spec/client_server/latest.html#get-matrix-media-r0-download-servername-mediaid
See https://github.com/vector-im/riot-web/issues/1977 and
https://developer.github.com/changes/2014-04-25-user-content-security for more details.
Whilst we make a reasonable effort to mitigate against XSS attacks (for
instance, by using `CSP`_), a Matrix homeserver should not be hosted on a
domain hosting other web applications. This especially applies to sharing
the domain with Matrix web clients and other sensitive applications like
webmail. See
https://developer.github.com/changes/2014-04-25-user-content-security for more
information.
.. _CSP: https://github.com/matrix-org/synapse/pull/1021
Ideally, the homeserver should not simply be on a different subdomain, but on
a completely different `registered domain`_ (also known as top-level site or
eTLD+1). This is because `some attacks`_ are still possible as long as the two
applications share the same registered domain.
.. _registered domain: https://tools.ietf.org/html/draft-ietf-httpbis-rfc6265bis-03#section-2.3
.. _some attacks: https://en.wikipedia.org/wiki/Session_fixation#Attacks_using_cross-subdomain_cookie
To illustrate this with an example, if your Element Web or other sensitive web
application is hosted on ``A.example1.com``, you should ideally host Synapse on
``example2.com``. Some amount of protection is offered by hosting on
``B.example1.com`` instead, so this is also acceptable in some scenarios.
However, you should *not* host your Synapse on ``A.example1.com``.
Note that all of the above refers exclusively to the domain used in Synapse's
``public_baseurl`` setting. In particular, it has no bearing on the domain
mentioned in MXIDs hosted on that server.
Following this advice ensures that even if an XSS is found in Synapse, the
impact to other applications will be minimal.
Upgrading an existing Synapse

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changelog.d/9221.doc Normal file
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Clarify security note regarding hosting Synapse on the same domain as other web applications.