Denial of Service in h2oai/h2o-3

Vulnerability

Overview

The /3/ImportFiles endpoint in h2oai/h2o-3 version 3.46.1 contains a vulnerability that can be exploited to cause a denial of service [1][2]. The endpoint accepts a single GET parameter, path, and processes it to import files. The flaw lies in the endpoint's handling of the path parameter, which can be set to reference the endpoint itself recursively [2].

Exploitation

Details

An attacker can exploit this by crafting a GET request to /3/ImportFiles where the path parameter is set to a value that causes the server to call its own endpoint repeatedly [2]. As the description indicates, setting path to reference itself leads the server to recursively invoke the ImportFiles handler, generating an endless chain of internal requests. This does not require authentication, making it exploitable by any remote attacker who can reach the server [2].

The relevant source code is located in h2o-core/src/main/java/water/api/ImportFilesHandler.java [3]. The handler's implementation does not prevent recursive or self-referential path values, allowing an attacker to trigger uncontrolled recursion.

Impact

The immediate impact is denial of service: the recursive requests fill up the server's request queue, exhausting resources and preventing the server from handling legitimate user requests [2]. This can render the H2O-3 instance unavailable for machine learning tasks and other operations until the queue is cleared or the server is restarted.

Mitigation

Status

As of the publication date, no patch or workaround has been mentioned in the provided references. Users are advised to restrict network access to the /3/ImportFiles endpoint or apply input validation to prevent recursive path references [2]. The vulnerability is under review and may be addressed in future releases.