CVE-2018-6536 in Icinga
Summary
by MITRE
An issue was discovered in Icinga 2.x through 2.8.1. The daemon creates an icinga2.pid file after dropping privileges to a non-root account, which might allow local users to kill arbitrary processes by leveraging access to this non-root account for icinga2.pid modification before a root script executes a "kill `cat /pathname/icinga2.pid`" command, as demonstrated by icinga2.init.d.cmake.
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability identified as CVE-2018-6536 represents a privilege escalation risk within Icinga 2 monitoring software versions 2.8.1 and earlier. This issue stems from improper handling of process identification files during the daemon startup sequence, creating a window of opportunity for local attackers to manipulate system processes through deliberate file modification attacks. The vulnerability specifically affects the daemon's behavior when transitioning from root privileges to non-root user accounts, leaving critical system resources temporarily accessible to lower-privileged users.
The technical flaw manifests in the daemon's creation of an icinga2.pid file while operating under non-root privileges, which creates a race condition scenario. When a root script subsequently executes a command to kill processes based on the contents of this pid file, local users with access to the non-root account can modify the file contents before the root script executes. This manipulation allows attackers to redirect the kill command to target arbitrary processes instead of the intended icinga2 daemon, effectively enabling process termination of any running application on the system. The vulnerability is particularly concerning because it leverages the legitimate administrative script execution pattern while exploiting a timing window in privilege management.
The operational impact of this vulnerability extends beyond simple process termination capabilities, as it provides attackers with a method to disrupt critical system services and potentially escalate privileges further. Attackers can target the icinga2 daemon itself, system daemons, or other critical services, leading to service disruption and potential system instability. The vulnerability operates through a classic race condition attack pattern where the attacker modifies the pid file between the time the daemon creates it and when the root script attempts to terminate processes. This timing attack requires minimal privileges but can result in significant system compromise, particularly in environments where Icinga 2 is used for critical infrastructure monitoring.
The attack vector for this vulnerability is particularly relevant in environments where multiple users have access to non-root accounts or where Icinga 2 operates in shared hosting environments. The exploitation process involves modifying the icinga2.pid file to contain the process identifier of a target service, followed by waiting for the root script execution that will terminate the specified process. This vulnerability aligns with CWE-362, which describes a race condition flaw that occurs when a program's execution sequence creates a window of opportunity for malicious interference. The attack pattern also corresponds to ATT&CK technique T1059.001 for command and scripting interpreter execution, as the exploitation requires manipulation of system scripts and command execution flows.
Mitigation strategies for CVE-2018-6536 should focus on addressing the race condition through proper file permissions and atomic operations during daemon startup. System administrators should ensure that pid files are created with appropriate permissions that prevent modification by non-root users, and that the daemon implements atomic file creation operations to eliminate the timing window. The recommended solution involves upgrading to Icinga 2 version 2.8.2 or later, where the vulnerability has been patched through improved privilege management and file handling procedures. Additionally, implementing proper file system permissions and using secure file creation patterns can help prevent similar vulnerabilities in other applications that follow similar operational models. Organizations should also consider implementing monitoring for unauthorized modifications to critical system files and establish proper access controls to prevent unauthorized users from gaining access to accounts that could be leveraged for such attacks.