diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8cb522f..ebac236 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,14 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+## [4.2.0] - 2020-12-09
+
+### Changed
+
++ Based Docker image on Python 3.9
++ Updated hydrus server version
++ Updated dependencies
+
 ## [4.1.0] - 2020-11-11
 
 ### Changed
@@ -384,7 +392,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 + Initial release
 
-[Unreleased]: https://github.com/imtbl/hydrus-server-docker/compare/4.1.0...develop
+[Unreleased]: https://github.com/imtbl/hydrus-server-docker/compare/4.2.0...develop
+[4.2.0]: https://github.com/imtbl/hydrus-server-docker/compare/4.1.0...4.2.0
 [4.1.0]: https://github.com/imtbl/hydrus-server-docker/compare/4.0.0...4.1.0
 [4.0.0]: https://github.com/imtbl/hydrus-server-docker/compare/3.29.0...4.0.0
 [3.29.0]: https://github.com/imtbl/hydrus-server-docker/compare/3.28.0...3.29.0
diff --git a/Dockerfile b/Dockerfile
index a9f969a..016c587 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -14,7 +14,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-FROM python:3.8-slim-buster
+FROM python:3.9-slim-buster
 
 ARG USER_ID=1000
 ARG GROUP_ID=1000
@@ -43,13 +43,13 @@ RUN \
   pip install \
     beautifulsoup4~=4.9.3 \
     chardet~=3.0.4 \
-    lz4~=3.1.0 \
+    lz4~=3.1.1 \
     numpy~=1.19.4 \
     opencv-python-headless~=4.4.0.46 \
     pillow~=8.0.1 \
     psutil~=5.7.3 \
     pylzma~=0.5.0 \
-    pyopenssl~=19.1.0 \
+    pyopenssl~=20.0.0 \
     pyyaml~=5.3.1 \
     requests~=2.25.0 \
     send2trash~=1.5.0 \
diff --git a/README.md b/README.md
index 3577ea0..78332e0 100644
--- a/README.md
+++ b/README.md
@@ -5,7 +5,7 @@
 This is a simple Debian-based Docker setup for running
 [hydrus server][hydrus-server] from source.
 
-The latest build runs [hydrus server version 417][hydrus-server-version].
+The latest build runs [hydrus server version 421][hydrus-server-version].
 
 Due to time constraints and the fact that changes to hydrus server are
 infrequent, a new release of this Docker setup is only made roughly
@@ -40,7 +40,7 @@ By default, this will pull the latest build. To specify an image with a
 specific version of hydrus server, provide the version number as tag, e.g.:
 
 ```zsh
-user@local:~$ docker pull mtbl/hydrus-server-docker:417
+user@local:~$ docker pull mtbl/hydrus-server-docker:421
 ```
 
 Alternatively, you can also build the image yourself:
@@ -162,13 +162,13 @@ You are welcome to help out!
 [AGPLv3](LICENSE) © imtbl
 
 [hydrus-server]: http://hydrusnetwork.github.io/hydrus/
-[hydrus-server-version]: https://github.com/hydrusnetwork/hydrus/releases/tag/v417
+[hydrus-server-version]: https://github.com/hydrusnetwork/hydrus/releases/tag/v421
 [docker-hub]: https://hub.docker.com/r/mtbl/hydrus-server-docker/
 [docker-hub-tags]: https://hub.docker.com/r/mtbl/hydrus-server-docker/tags/
 [docker]: https://www.docker.com/
 [semantic-versioning]: https://semver.org/
 
-[hydrus-server-badge]: https://img.shields.io/badge/hydrus%20server-version%20417-blue.svg
+[hydrus-server-badge]: https://img.shields.io/badge/hydrus%20server-version%20421-blue.svg
 
 [travis]: https://travis-ci.com/imtbl/hydrus-server-docker
 [travis-badge]: https://travis-ci.com/imtbl/hydrus-server-docker.svg
diff --git a/hydrus b/hydrus
index b2d0e31..c3100f7 160000
--- a/hydrus
+++ b/hydrus
@@ -1 +1 @@
-Subproject commit b2d0e31b8705e698d1672275e6d1a9cdea556f5b
+Subproject commit c3100f7a881b8a8b9ab4dd238d2696500c343d45