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How to harden a Traefik container (and is traefik:v3.2 safe at your edge?)

Traefik sits at the edge: it terminates TLS, routes every inbound request, and often reads the Docker or Kubernetes API to discover backends. That makes it both the first thing an attacker reaches and one of the most privileged processes in a stack, and a stock docker run traefik:v3.2 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 a reverse proxy needs by definition: it exists to accept and forward traffic. Here are the exact gaps and fixes from the scan data.

Every number here comes from a read-only docker inspect of traefik:v3.2, 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 traefik:v3.2, 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

For an edge proxy, the one that should worry you most is root. Traefik parses attacker-controlled bytes on every request; a routing or TLS CVE that lands code execution in a root container escapes as root on the host, next to the certificates and the API credentials it uses for service discovery. The full capability set widens that foothold and the writable rootfs makes it durable. A common Traefik pattern is mounting docker.sock for discovery; do not, and note that this scan would fail the docker.sock dimension if you did (use the Docker API over a scoped socket-proxy or the Kubernetes provider instead).

Harden it: the exact --fix remediation

ironctl scan my-traefik --fix prints one remediation per failed dimension, then one hardened run. For traefik:v3.2:

  • --user 65532:65532 (Non-root user, +15): pin a non-root uid so an escape does not begin as host uid 0. Traefik binds 80 and 443 by default; either map them to high host ports, or grant just CAP_NET_BIND_SERVICE (see below) so an unprivileged uid can bind the low ports.
  • --cap-drop=ALL (Dropped capabilities, +16): drop every Linux capability, then add back only CAP_NET_BIND_SERVICE if you must bind 80/443 directly. The scan below reflects dropping the full set with ports mapped high; adding one cap back costs 4 points (a WARN, still grade B territory).
  • --read-only --tmpfs /tmp (Read-only rootfs, +10): make the root filesystem read-only. Traefik runs happily read-only; mount an ACME storage volume if you use its built-in Let's Encrypt.
  • Scoped network (Network isolation): --network=none scores the full 15 but is wrong for a proxy, it exists to forward traffic. Any named or bridge network scores 4 of 15 (a WARN, not a fail): a connection path exists. Contain it anyway: put Traefik on a user-defined network scoped to just the backends it fronts, with no default route out, so a compromised proxy cannot call arbitrary internet addresses.

Before and after

# Before: 48/100, grade D
docker run -d --name traefik traefik:v3.2

# After: 89/100, grade B (scoped private network for its backends)
docker run -d --name traefik-hardened \
  --user 65532:65532 \
  --cap-drop=ALL \
  --security-opt=no-new-privileges \
  --read-only --tmpfs /tmp \
  -p 8080:8080 -p 8443:8443 \
  --network=edge-internal \
  traefik:v3.2

Rescan: ironctl scan traefik-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 a reverse proxy exists to accept connections; network=none would score the last points but leave nothing able to reach or be reached. That is the honest ceiling for a proxy, and it is a long way from the default D.

Verify it on your own Traefik

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

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

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

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