diff --git a/CHANGES.md b/CHANGES.md
index e3550497a4..f794c585b7 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,63 @@
+Synapse 1.12.0 (2020-03-23)
+===========================
+
+No significant changes since 1.12.0rc1.
+
+Debian packages and Docker images are rebuilt using the latest versions of
+dependency libraries, including Twisted 20.3.0. **Please see security advisory
+below**.
+
+Security advisory
+-----------------
+
+Synapse may be vulnerable to request-smuggling attacks when it is used with a
+reverse-proxy. The vulnerabilties are fixed in Twisted 20.3.0, and are
+described in
+[CVE-2020-10108](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10108)
+and
+[CVE-2020-10109](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10109).
+For a good introduction to this class of request-smuggling attacks, see
+https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn.
+
+We are not aware of these vulnerabilities being exploited in the wild, and
+do not believe that they are exploitable with current versions of any reverse
+proxies. Nevertheless, we recommend that all Synapse administrators ensure that
+they have the latest versions of the Twisted library to ensure that their
+installation remains secure.
+
+* Administrators using the [`matrix.org` Docker
+  image](https://hub.docker.com/r/matrixdotorg/synapse/) or the [Debian/Ubuntu
+  packages from
+  `matrix.org`](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#matrixorg-packages)
+  should ensure that they have version 1.12.0 installed: these images include
+  Twisted 20.3.0.
+* Administrators who have [installed Synapse from
+  source](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#installing-from-source)
+  should upgrade Twisted within their virtualenv by running:
+  ```sh
+  <path_to_virtualenv>/bin/pip install 'Twisted>=20.3.0'
+  ```
+* Administrators who have installed Synapse from distribution packages should
+  consult the information from their distributions.
+
+The `matrix.org` Synapse instance was not vulnerable to these vulnerabilities.
+
+Advance notice of change to the default `git` branch for Synapse
+----------------------------------------------------------------
+
+Currently, the default `git` branch for Synapse is `master`, which tracks the
+latest release.
+
+After the release of Synapse 1.13.0, we intend to change this default to
+`develop`, which is the development tip. This is more consistent with common
+practice and modern `git` usage.
+
+Although we try to keep `develop` in a stable state, there may be occasions
+where regressions creep in. Developers and distributors who have scripts which
+run builds using the default branch of `Synapse` should therefore consider
+pinning their scripts to `master`.
+
+
 Synapse 1.12.0rc1 (2020-03-19)
 ==============================
 
diff --git a/debian/changelog b/debian/changelog
index c39ea8f47f..39ec9da7ab 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.12.0) stable; urgency=medium
+
+  * New synapse release 1.12.0.
+
+ -- Synapse Packaging team <packages@matrix.org>  Mon, 23 Mar 2020 12:13:03 +0000
+
 matrix-synapse-py3 (1.11.1) stable; urgency=medium
 
   * New synapse release 1.11.1.
diff --git a/docs/postgres.md b/docs/postgres.md
index 16a630c3d1..04aa746051 100644
--- a/docs/postgres.md
+++ b/docs/postgres.md
@@ -72,8 +72,7 @@ underneath the database, or if a different version of the locale is used on any
 replicas.
 
 The safest way to fix the issue is to take a dump and recreate the database with
-the correct `COLLATE` and `CTYPE` parameters (as per
-[docs/postgres.md](docs/postgres.md)). It is also possible to change the
+the correct `COLLATE` and `CTYPE` parameters (as shown above). It is also possible to change the
 parameters on a live database and run a `REINDEX` on the entire database,
 however extreme care must be taken to avoid database corruption.
 
diff --git a/synapse/__init__.py b/synapse/__init__.py
index 020e0536be..5b86008945 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -36,7 +36,7 @@ try:
 except ImportError:
     pass
 
-__version__ = "1.12.0rc1"
+__version__ = "1.12.0"
 
 if bool(os.environ.get("SYNAPSE_TEST_PATCH_LOG_CONTEXTS", False)):
     # We import here so that we don't have to install a bunch of deps when