Checkmk Werk 14385: Fix limited SSRF in agent-receiver API

ID: 14385 Title: Fix limited SSRF in agent-receiver API Component: Core & setup Level: 1 Class: Security fix Version: 2.2.0i1 Prior to this Werk attackers could use the host registration API for Server Side Request Forgery. An attacker would have been able to make the Checkmk server issue local requests to endpoints that should only be accessible from localhost. In order to exploit this vulnerability attackers would have needed the privileges to register hosts. This vulnerability was caused by insufficient sanitization of the hostname of the host to be registered. We thank Stefan Schiller (SonarSource) for reporting this issue. <b>Affected Versions</b>: 2.1 <b>Mitigations</b>: The affected API can be disabled using <tt>omd stop agent-receiver</tt>. Note however, that this makes it impossible to register new hosts. <b>Vulnerability Management</b>: We have rated the issue with a CVSS Score of 5.0 (Medium) with the following CVSS vector: <tt>CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N</tt>. A CVE has been requested. <b>Changes</b>: This Werk adds validation for the hostname and ensures hostnames are escaped in requests to the REST API.