diff --git a/CHANGES.md b/CHANGES.md
index d5e578ee3..677afeebc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,49 @@
+Synapse 1.24.0 (2020-12-09)
+===========================
+
+Due to the two security issues highlighted below, server administrators are
+encouraged to update Synapse. We are not aware of these vulnerabilities being
+exploited in the wild.
+
+Security advisory
+-----------------
+
+The following issues are fixed in v1.23.1 and v1.24.0.
+
+- There is a denial of service attack
+  ([CVE-2020-26257](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26257))
+  against the federation APIs in which future events will not be correctly sent
+  to other servers over federation. This affects all servers that participate in
+  open federation. (Fixed in [#8776](https://github.com/matrix-org/synapse/pull/8776)).
+
+- Synapse may be affected by OpenSSL
+  [CVE-2020-1971](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-1971).
+  Synapse administrators should ensure that they have the latest versions of
+  the cryptography Python package installed.
+
+To upgrade Synapse along with the cryptography package:
+
+* 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 1.24.0 or 1.23.1 installed: these images include
+  the updated packages.
+* Administrators who have [installed Synapse from
+  source](https://github.com/matrix-org/synapse/blob/master/INSTALL.md#installing-from-source)
+  should upgrade the cryptography package within their virtualenv by running:
+  ```sh
+  <path_to_virtualenv>/bin/pip install 'cryptography>=3.3'
+  ```
+* Administrators who have installed Synapse from distribution packages should
+  consult the information from their distributions.
+
+Internal Changes
+----------------
+
+- Add a maximum version for pysaml2 on Python 3.5. ([\#8898](https://github.com/matrix-org/synapse/issues/8898))
+
+
 Synapse 1.24.0rc2 (2020-12-04)
 ==============================
 
diff --git a/debian/changelog b/debian/changelog
index 4ea4feddd..9f47d12b7 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.24.0) stable; urgency=medium
+
+  * New synapse release 1.24.0.
+
+ -- Synapse Packaging team <packages@matrix.org>  Wed, 09 Dec 2020 10:14:30 +0000
+
 matrix-synapse-py3 (1.23.0) stable; urgency=medium
 
   * New synapse release 1.23.0.
diff --git a/synapse/__init__.py b/synapse/__init__.py
index 2e354f2cc..f2d3ac68e 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -48,7 +48,7 @@ try:
 except ImportError:
     pass
 
-__version__ = "1.24.0rc2"
+__version__ = "1.24.0"
 
 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
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index c899ca14d..c97e0df1f 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -96,7 +96,11 @@ CONDITIONAL_REQUIREMENTS = {
         # python 3.5.2, as per https://github.com/itamarst/eliot/issues/418
         'eliot<1.8.0;python_version<"3.5.3"',
     ],
-    "saml2": ["pysaml2>=4.5.0"],
+    "saml2": [
+        # pysaml2 6.4.0 is incompatible with Python 3.5 (see https://github.com/IdentityPython/pysaml2/issues/749)
+        "pysaml2>=4.5.0,<6.4.0;python_version<'3.6'",
+        "pysaml2>=4.5.0;python_version>='3.6'",
+    ],
     "oidc": ["authlib>=0.14.0"],
     "systemd": ["systemd-python>=231"],
     "url_preview": ["lxml>=3.5.0"],