diff --git a/Dockerfile b/Dockerfile
index 7e4ba0f..2f6748d 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,8 +1,8 @@
-FROM tomcat:jdk11-openjdk-slim
+FROM tomcat:9.0.41-jdk11-openjdk-slim AS base
 
-ARG GEOSERVER_VERSION=2.18.1
+ARG GEOSERVER_VERSION=2.18.2
 
-ARG WAR_URL=https://downloads.sourceforge.net/project/geoserver/GeoServer/${GEOSERVER_VERSION}/geoserver-${GEOSERVER_VERSION}-war.zip
+ARG GEOSERVER_WAR_SRC=https://downloads.sourceforge.net/project/geoserver/GeoServer/${GEOSERVER_VERSION}/geoserver-${GEOSERVER_VERSION}-war.zip
 ARG STABLE_PLUGIN_URL=https://sourceforge.net/projects/geoserver/files/GeoServer/${GEOSERVER_VERSION}/extensions
 
 ARG CORS_ENABLED=false
@@ -32,15 +32,15 @@ RUN apt update && \
     apt install -y curl wget openssl zip fontconfig libfreetype6 && \
     rm -rf ${CATALINA_HOME}/webapps/*
 
+ADD "${GEOSERVER_WAR_SRC}" "/tmp/"
+
 # install geoserver
-RUN wget --progress=bar:force:noscroll -c --no-check-certificate "${WAR_URL}" -O /tmp/geoserver.zip && \
-    unzip /tmp/geoserver.zip geoserver.war -d ${CATALINA_HOME}/webapps && \
-    mkdir -p ${GEOSERVER_DIR} && \
-    unzip -q ${CATALINA_HOME}/webapps/geoserver.war -d ${GEOSERVER_DIR} && \
+RUN unzip /tmp/geoserver*.zip geoserver.war -d ${CATALINA_HOME}/webapps && \
+    mkdir -p ${GEOSERVER_DIR} && \unzip -q ${CATALINA_HOME}/webapps/geoserver.war -d ${GEOSERVER_DIR} && \
     rm ${CATALINA_HOME}/webapps/geoserver.war
 
 # configure CORS (inspired by https://github.com/oscarfonts/docker-geoserver)
-RUN if [ "$CORS_ENABLED" = "true" ]; then \
+RUN if [ "${CORS_ENABLED}" = "true" ]; then \
       sed -i "\:</web-app>:i\ \
       <filter>\n\ \
         <filter-name>CorsFilter</filter-name>\n\ \
diff --git a/README.md b/README.md
index a2a97f8..6f4441e 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,10 @@ Work is still in progress!
 
 1. The [Dockerfile](Dockerfile)
     1. installs dependencies
-    1. installs the GeoServer by downloading and extracting the war file
+    1. installs the GeoServer by adding a ZIP and extracting the WAR from it
+       1. the expected file name of the war in the zip is `geoserver.war`
+       1. by default, the GeoServer URL from sourceforge is used, but you could also provide a custom URL with a zip in the `GEOSERVER_WAR_SRC` build argument.
+       1. you can also use the `GEOSERVER_WAR_SRC` build argument to burn your custom WAR file from your local machine to the docker image, e.g. with something like `docker build -t geoserver:test --build-arg GEOSERVER_WAR_SRC="./resources/geoserver.zip" .`
     1. defines defaults for environment variables
 1. The [entrypoint.sh](scripts/entrypoint.sh) startup script (in a running container)
     1. executes [install-extensions.sh](scripts/install-extensions.sh) to download and install GeoServer extensions based on the `STABLE_EXTENSIONS` environment variable.
diff --git a/docker-compose-demo.yml b/docker-compose-demo.yml
index de2385a..df67b48 100644
--- a/docker-compose-demo.yml
+++ b/docker-compose-demo.yml
@@ -4,7 +4,7 @@ services:
     build:
       context: .
       args:
-        - GEOSERVER_VERSION=2.18.1
+        - GEOSERVER_VERSION=2.18.2
         - CORS_ENABLED=true
         - CORS_ALLOWED_METHODS=GET,POST,PUT,HEAD,OPTIONS
     ports: