Executive brief
Kestra, an open-source workflow orchestration platform, contains a vulnerability in its Pebble template engine that allows attackers to make arbitrary HTTP requests to internal services and cloud metadata endpoints without authentication. An attacker can import a malicious workflow and retrieve sensitive cloud credentials (AWS/GCP/Azure), access internal services, or interact with localhost endpoints, potentially leading to credential theft and lateral movement within cloud environments.
Technical details
The vulnerability is a Server-Side Request Forgery (SSRF) in the Pebble template engine's http() function (HttpFunction.java, lines 77–106). The root cause is the lack of URL validation: user-supplied URLs are passed directly to URI.create() without checks for private IP ranges (10.0.0.0/8, 192.168.0.0/16, 127.0.0.1), cloud metadata endpoints (169.254.169.254), or restricted URL schemes (file://, gopher://). Additionally, no authentication is enforced beyond a basic tenant check for "main", and the HttpFunction is unconditionally registered. An unauthenticated attacker can import a malicious workflow YAML file and execute it to trigger HTTP requests from the server, bypassing network perimeter controls to access internal systems and metadata services.
Affected products
- Kestra Kestra all versions (OSS)
Timeline
- 2026-09-17: disclosed: Advisory GHSA-r56g-q4p6-m3p6 published