CVE-2020-14004 in Icinga2
Summary
by MITRE
An issue was discovered in Icinga2 before v2.12.0-rc1. The prepare-dirs script (run as part of the icinga2 systemd service) executes chmod 2750 /run/icinga2/cmd. /run/icinga2 is under control of an unprivileged user by default. If /run/icinga2/cmd is a symlink, then it will by followed and arbitrary files can be changed to mode 2750 by the unprivileged icinga2 user.
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Analysis
by VulDB Data Team • 10/24/2020
The vulnerability described in CVE-2020-14004 represents a critical privilege escalation issue within the Icinga2 monitoring system, specifically affecting versions prior to v2.12.0-rc1. This flaw exists in the prepare-dirs script that is executed as part of the icinga2 systemd service initialization process. The vulnerability stems from improper handling of directory permissions and symbolic link resolution during the service startup sequence, creating a path traversal condition that allows unprivileged users to manipulate file permissions in system directories.
The technical implementation of this vulnerability involves the execution of chmod 2750 command on the /run/icinga2/cmd directory path. Under normal circumstances, the /run/icinga2 directory is managed by an unprivileged user by default, which creates a security boundary. However, when the /run/icinga2/cmd path is a symbolic link, the chmod operation follows the symlink and modifies permissions of the target file or directory that the symlink points to, rather than the intended location. This behavior creates a privilege escalation vector because the unprivileged icinga2 user can manipulate permissions of arbitrary files on the system, effectively allowing them to gain elevated privileges.
The operational impact of this vulnerability is significant as it enables an attacker with minimal privileges to modify file permissions across the system filesystem. The chmod 2750 operation sets specific permissions that grant read, write, and execute access to the owner and group, while restricting access to others. This permission change can potentially allow an attacker to modify critical system files, create backdoors, or establish persistent access to the system. The vulnerability affects the core system integrity by undermining the privilege separation mechanisms that should protect system directories from unauthorized modification by non-privileged users.
From a cybersecurity perspective, this vulnerability aligns with CWE-59: Improper Link Following, which addresses the improper handling of symbolic links in security contexts. The issue also maps to ATT&CK technique T1068: Exploitation for Privilege Escalation, as it provides a mechanism for unprivileged users to gain elevated system privileges. The vulnerability demonstrates a classic path traversal flaw where the system fails to properly validate or sanitize symbolic link targets before performing permission modifications. Organizations using Icinga2 should immediately upgrade to version v2.12.0-rc1 or later to address this vulnerability, as the exploit requires no special privileges beyond basic user access and can be executed automatically during service startup.
The root cause of this issue lies in the lack of proper input validation and path sanitization within the prepare-dirs script. The script does not verify whether the target path is a symbolic link before executing the chmod operation, creating a window where an attacker can manipulate the symbolic link to point to any desired file or directory on the system. This design flaw represents a failure in the principle of least privilege, where a service running with limited privileges can inadvertently gain broader system access through improper permission handling. The vulnerability underscores the importance of proper symbolic link validation in security-critical system components and highlights the necessity of implementing robust input sanitization measures in all system initialization scripts that perform permission modifications.