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How to harden a Keycloak container (and is quay.io/keycloak/keycloak safe as your IdP?)

Keycloak is the front door to every app behind it: it mints the tokens, holds the signing keys, and stores the user directory that authenticates your whole stack. A stock docker run quay.io/keycloak/keycloak is not the boundary that role deserves. Graded on IronClaw's seven-dimension containment scale, the default configuration scores 48 of 100, grade D (porous). Higher is safer. A few runtime flags take the same image to 89 of 100, grade B, one point off an A, and the one dimension it cannot reach is the one an identity provider needs by definition: every app and browser must reach its endpoints. Here are the exact gaps and fixes from the scan data.

Every number here comes from a read-only docker inspect of quay.io/keycloak/keycloak, the same data behind its isolation scorecard. No workload is executed. How scoring works →

Where the default configuration leaks

ironctl scan grades seven independent containment boundaries. On a default docker run quay.io/keycloak/keycloak, three fail and one warns:

Dimension Verdict Score What the scan found
Non-root user (uid != 0) ❌ FAIL 0/15 runs as root (uid 0); a container escape starts with host-uid 0
Dropped capabilities ❌ FAIL 4/20 default capability set retained (CAP_NET_RAW, CAP_MKNOD, and more)
Seccomp profile ✅ PASS 15/15 seccomp profile active
Network isolation / egress ⚠️ WARN 4/15 network=bridge: outbound egress is possible
Read-only root filesystem ❌ FAIL 0/10 root filesystem is writable
No docker.sock exposure ✅ PASS 15/15 no control socket mounted
No shared host namespaces ✅ PASS 10/10 no host PID/IPC/network sharing

The one that should worry you most is root, and for an identity provider the stakes are the whole trust chain. A protocol-parsing or provider CVE that lands code execution in a root container escapes as root on the host, next to the realm signing keys and the user store Keycloak guards. Whoever holds those keys can mint a valid token for any user of any app behind Keycloak. The full capability set widens that foothold and the writable rootfs makes it durable. This is the same shape as a secrets server: the value of what it holds is what makes containing it non-negotiable.

Harden it: the exact --fix remediation

ironctl scan my-keycloak --fix prints one remediation per failed dimension, then one hardened run. For quay.io/keycloak/keycloak:

  • --user 1000:1000 (Non-root user, +15): pin the non-root uid the image already ships with so an escape does not begin as host uid 0.
  • --cap-drop=ALL (Dropped capabilities, +16): drop every Linux capability; Keycloak serves its HTTP and management endpoints on high ports and needs none of the default set.
  • --read-only --tmpfs /tmp (Read-only rootfs, +10): make the root filesystem read-only. Build a configured image with kc.sh build ahead of time and point the data directory at a volume, so the running container needs no writable root.
  • Scoped network (Network isolation): --network=none scores the full 15 but is wrong for an identity provider, every app and browser must reach it. Any named or bridge network scores 4 of 15 (a WARN, not a fail): a connection path exists. Contain it anyway: put Keycloak on a user-defined network scoped to just its database and the reverse proxy that fronts it, with no default route out, so a compromised process cannot call arbitrary internet addresses.

Before and after

# Before: 48/100, grade D
docker run -d --name keycloak quay.io/keycloak/keycloak:26.0 start

# After: 89/100, grade B (scoped private network for its database and proxy)
docker run -d --name keycloak-hardened \
  --user 1000:1000 \
  --cap-drop=ALL \
  --security-opt=no-new-privileges \
  --read-only --tmpfs /tmp \
  --network=auth-internal \
  quay.io/keycloak/keycloak:26.0 start

Rescan: ironctl scan keycloak-hardened reports 89/100 grade B. A 41-point swing with no custom image build, just the right flags. The only dimension still short of full marks is the network (4 of 15), because an identity provider exists to be reached by every app it authenticates; network=none would score the last points but leave nothing able to connect. That is the honest ceiling for this role, and it is a long way from the default D.

Verify it on your own Keycloak

# install (Homebrew)
brew install ironsecco/ironclaw/ironclaw

# grade your running container, then print the fixes
ironctl scan my-keycloak
ironctl scan my-keycloak --fix

ironctl scan also reads a docker-compose.yml service or a Kubernetes manifest, so you can grade the Keycloak in your stack, not just a bare docker run.

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