Attack Chain

1. An unauthenticated attacker sends an HTTP POST request to the Nuclio Dashboard API's /api/functions endpoint.
2. The request body includes a malicious runtimeAttributes.repositories field within the function definition, containing Groovy code designed to break out of the repositories {} block and execute arbitrary commands.
3. The Dashboard API receives the request; due to default NOP authentication, no credentials or input validation are performed on the runtimeAttributes.repositories content.
4. The newBuildAttributes() function decodes the runtimeAttributes without content inspection, allowing the malicious string to pass through.
5. The createGradleBuildScript() function uses Go's text/template engine to render the runtimeAttributes.repositories verbatim into the build.gradle file, without any contextual escaping.
6. The generated build.gradle file now contains the attacker's injected Groovy code as top-level statements.
7. The build process, executed by ./build-user-handler.sh inside the quay.io/nuclio/handler-builder-java-onbuild container, invokes gradle tasks and gradle userHandler.
8. During Gradle's configuration phase, the injected Groovy statements are evaluated, executing the attacker's arbitrary commands (e.g., id && hostname && whoami) with root privileges (uid=0) inside the build container.

Impact

Successful exploitation of this vulnerability results in unauthenticated remote code execution with root privileges on the Nuclio build container. An attacker can execute arbitrary commands, leading to full compromise of the build environment, potential data exfiltration, supply chain attacks by injecting malicious code into compiled artifacts, or further lateral movement within the hosting Kubernetes cluster. The proof-of-concept demonstrated execution of id && hostname && whoami commands, returning uid=0(root) gid=0(root) groups=0(root), confirming maximum privileges.

Recommendation

• Patch Nuclio deployments immediately to a version greater than 1.15.27 (once available) as this version is confirmed vulnerable.
• Monitor process_creation logs on Linux build containers for suspicious shell command execution (e.g., sh -c followed by system enumeration commands like id, whoami, hostname) with java as a parent process running gradle, as described in the detection rule below.
• Implement robust authentication and authorization for the Nuclio Dashboard API, moving away from NOP authentication, to prevent unauthenticated access.