diff --git a/Dockerfile b/Dockerfile
index 97d71f1f..141d03e4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,8 +1,8 @@
-FROM eclipse-temurin:11.0.22_7-jdk-jammy AS builder
+FROM eclipse-temurin:21-jdk-jammy AS builder
 COPY . /usr/src/openas2
 WORKDIR /usr/src/openas2
 # To test Locally builder environment:
-# docker run --rm -it -v $(pwd):/usr/src/openas2 openjdk:11 bash
+# docker run --rm -it -v $(pwd):/usr/src/openas2 eclipse-temurin:21-jdk-jammy bash
 RUN apt update
 RUN apt-get install -y unzip
 RUN rm -f Server/dist/*
@@ -18,7 +18,7 @@ RUN cd /usr/src/openas2/Runtime/bin && \
     mv config config_template
 
 
-FROM eclipse-temurin:11.0.22_7-jre-jammy
+FROM eclipse-temurin:21-jre-jammy
 ENV OPENAS2_BASE=/opt/openas2
 ENV OPENAS2_HOME=/opt/openas2
 ENV OPENAS2_TMPDIR=/opt/openas2/temp
@@ -26,6 +26,14 @@ COPY --from=builder /usr/src/openas2/Runtime/bin ${OPENAS2_BASE}/bin
 COPY --from=builder /usr/src/openas2/Runtime/lib ${OPENAS2_BASE}/lib
 COPY --from=builder /usr/src/openas2/Runtime/resources ${OPENAS2_BASE}/resources
 COPY --from=builder /usr/src/openas2/Runtime/config_template ${OPENAS2_HOME}/config_template
-RUN mkdir ${OPENAS2_BASE}/config
+# Run as an unprivileged user rather than root, since the server is usually exposed to the internet.
+# The user is in group 0 and everything it writes is group writable, so platforms that run the
+# container under an arbitrary user ID in group 0 work as well. The ID is numeric in USER so that
+# Kubernetes can verify runAsNonRoot.
+RUN useradd --uid 1000 --gid 0 --home-dir ${OPENAS2_HOME} --no-create-home --shell /usr/sbin/nologin openas2 \
+    && mkdir -p ${OPENAS2_BASE}/config ${OPENAS2_BASE}/data ${OPENAS2_BASE}/logs ${OPENAS2_TMPDIR} \
+    && chown -R 1000:0 ${OPENAS2_BASE} \
+    && chmod -R g=u ${OPENAS2_BASE}
+USER 1000
 WORKDIR $OPENAS2_HOME
 ENTRYPOINT ["/opt/openas2/bin/start-container.sh"]
\ No newline at end of file
diff --git a/README.md b/README.md
index 76441116..ec53e60c 100644
--- a/README.md
+++ b/README.md
@@ -76,10 +76,26 @@ You can then go to `http://localhost:4080` or `http://host-ip:4080` in a browser
 
 The default OpenAS2 environment in the image is:
 
-	OPENAS2_BASE:    /usr/local/tomcat
-	OPENAS2_HOME:    /usr/local/tomcat
-	OPENAS2_TMPDIR:  /usr/local/tomcat/temp
-	JAVA_HOME:       /usr/local/openjdk-11
+	OPENAS2_BASE:    /opt/openas2
+	OPENAS2_HOME:    /opt/openas2
+	OPENAS2_TMPDIR:  /opt/openas2/temp
+	JAVA_HOME:       /opt/java/openjdk (Java 21)
+
+### Running as a non-root user
+
+The image runs OpenAS2 as user `openas2` (UID `1000`) in group `0`, not as root. Anything mounted into the
+container that OpenAS2 writes to, normally `/opt/openas2/config` and `/opt/openas2/data`, must be writable by that
+user, or the server fails to start with `Permission denied`. A directory created by Docker for a bind mount is owned
+by root, so give it to the container user:
+
+```console
+$ sudo chown -R 1000:0 ./config ./data
+```
+
+A named Docker volume is initialised from the image the first time it is used, so it already has the right owner.
+
+To keep running as root instead, for example while existing volumes are migrated, override the user with
+`docker run --user 0`, or `user: "0"` in docker-compose.yml.
 
 The configuration files are available in `/opt/openas2/config/`.
 
diff --git a/RELEASE-NOTES.md b/RELEASE-NOTES.md
index 489af3a6..b8afee8f 100644
--- a/RELEASE-NOTES.md
+++ b/RELEASE-NOTES.md
@@ -9,6 +9,16 @@ The release download file is: OpenAS2Server-4.13.0.zip
 The zip file contains a PDF document (OpenAS2HowTo.pdf) providing information on installing and using the application.
 ## NOTE: Testing covers Java 17 to 21.
 
+Version UNRELEASED
+===========================
+
+This is a minor enhancement and bugfix release.
+1. Fix the Docker image failing to build, and run OpenAS2 in it as an unprivileged user instead of root (issue #367).
+   The image built on Java 11 but the project compiles for Java 17, so "docker build" failed with "invalid target
+   release: 17". Both stages now use Java 21. The server now runs as the user "openas2" (UID 1000, group 0), since it
+   is usually exposed to the internet. Volumes mounted for the config and data folders must be writable by that user:
+   see the upgrade notes in RELEASE-NOTES.md and the README.
+
 Version 4.14.0 2026-10-13
 ===========================
 
@@ -41,6 +51,13 @@ This is a minor enhancement and bugfix release.
 
  **You must review all notes for the relevant intermediate versions from your version to this release version.**
 
+### Upgrading to a version after 4.14.0 if you run the OpenAS2 Docker image:
+      1. The image now runs OpenAS2 as the unprivileged user "openas2" (UID 1000, group 0) instead of root. Volumes
+         mounted for /opt/openas2/config and /opt/openas2/data must be writable by that user or the server will fail to
+         start with "Permission denied". Change their ownership (for example "chown -R 1000:0 ./config ./data"), set
+         fsGroup in a Kubernetes pod securityContext, or keep running as root with "docker run --user 0" while the
+         volumes are migrated. See the README for details.
+
 ### Upgrading to 4.6.1 or newer from any older version if using parallel processing mode:
       1. Ensure you change the property for enabling parallel mode by removing the 3rd consecutive "l" from "process_files_in_paralllel".
 
diff --git a/changes.txt b/changes.txt
index fdb885bf..b33c5d24 100644
--- a/changes.txt
+++ b/changes.txt
@@ -1,5 +1,15 @@
 **IMPORTANT NOTE**: Please review upgrade notes in the RELEASE-NOTES.md if you are upgrading
 
+Version UNRELEASED
+===========================
+
+This is a minor enhancement and bugfix release.
+1. Fix the Docker image failing to build, and run OpenAS2 in it as an unprivileged user instead of root (issue #367).
+   The image built on Java 11 but the project compiles for Java 17, so "docker build" failed with "invalid target
+   release: 17". Both stages now use Java 21. The server now runs as the user "openas2" (UID 1000, group 0), since it
+   is usually exposed to the internet. Volumes mounted for the config and data folders must be writable by that user:
+   see the upgrade notes in RELEASE-NOTES.md and the README.
+
 Version 4.14.0 2026-10-13
 ===========================
 
diff --git a/k8s-deployment.md b/k8s-deployment.md
index f4ea28ab..3685aa63 100644
--- a/k8s-deployment.md
+++ b/k8s-deployment.md
@@ -63,6 +63,14 @@ spec:
       labels:
         app: openas2
     spec:
+      # The image runs as the unprivileged UID 1000. fsGroup makes block storage volumes writable by it;
+      # Azure Files and other SMB or NFS volumes ignore fsGroup, so set their ownership or permissions
+      # in the storage class mount options instead (for example uid=1000,gid=0).
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 1000
+        runAsGroup: 0
+        fsGroup: 1000
       containers:
         - name: openas2
           image: myrepo/openas2app:latest