CVE-2026-73973 in monitoring-plugins
Summary
by MITRE • 08/18/2026
Linuxfabrik Monitoring Plugins provides monitoring plugins for Icinga, Nagios, and related systems. Prior to version 7.0.0, check-plugins/logfile/logfile accepted a free-form --filename path and opened it as root when invoked through the shipped nagios or icinga sudoers allowlist, without confining the resolved path to /var/log. An attacker who controls the monitoring account can select a root-readable file such as /etc/shadow and use --warning-regex . while leaving SUPPRESS_OUTPUT false, causing each nonempty line to be collected in warn_matches and returned through lib.base.oao(). The vulnerable flow passes the expanded scan_path directly to open(), and neither real-path containment nor an allowlist protects the sink. The same fix also confines mysql-logfile and openvpn-client-list paths, allows only documented log roots, and resolves symlinks and parent-directory traversal before checking containment. This issue is fixed in version 7.0.0.
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Analysis
by VulDB Data Team • 08/18/2026
The Linuxfabrik Monitoring Plugins suite serves as a critical component for infrastructure observability, providing plugins compatible with major monitoring systems such as Icinga and Nagios. These tools are typically deployed to monitor system health by reading log files from standard directories like /var/log. In versions prior to 7.0.0, the check-plugins/logfile module contained a significant path traversal vulnerability that undermined the security boundaries established for these services. The plugin was designed to accept a free-form filename argument via the --filename parameter, which dictated the target file for monitoring. This design choice failed to enforce strict input validation or path canonicalization before processing the user-supplied value.
The core technical flaw lies in how the application handles the provided filepath during execution. When invoked through the standard sudoers allowlist configured for Nagios or Icinga users, the plugin executes with root privileges. The code passes the expanded scan_path directly to the open() system call without first resolving symlinks or validating that the resolved absolute path remains within an allowed directory structure such as /var/log. This lack of confinement means that if a user provides a relative path containing parent-directory traversal sequences, such as ../../etc/shadow, the application resolves this against the current working directory and attempts to open the specified file regardless of its actual location on the filesystem. There is no allowlist or real-path containment check in place at the sink point where the file descriptor is acquired.
The operational impact of this vulnerability is severe due to the elevated privileges under which the plugin operates. An attacker who has compromised a monitoring account, such as those used by Nagios or Icinga agents, can exploit this flaw to read arbitrary files on the host system that are accessible to root. By specifying sensitive configuration files like /etc/shadow in the filename argument and setting the warning regex to match all non-empty lines while suppressing output filtering, an attacker can force the plugin to collect and return the contents of these restricted files through the lib.base.oao() function. This effectively results in a full local file read vulnerability, allowing the extraction of password hashes, SSH keys, or other critical system credentials that are normally protected from unprivileged users.
This issue aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory and CWE-78: Improper Neutralization of Special Elements used in an OS Command, specifically regarding path traversal. From the perspective of the MITRE ATT&CK framework, this vulnerability facilitates Initial Access via compromised accounts and enables Lateral Movement or Credential Access through Local File Inclusion techniques. The exploitation chain relies on the attacker's ability to execute monitoring plugins with elevated privileges, a common pattern in many Linux-based monitoring deployments where agents run as root to gather comprehensive system metrics.
The remediation for this vulnerability was implemented in version 7.0.0 of the Linuxfabrik Monitoring Plugins. The fix introduces strict path confinement by resolving symlinks and normalizing parent-directory traversal sequences before performing any containment checks. The application now ensures that only documented log roots are accessible, effectively closing the gap where arbitrary file reads were previously possible. Additionally, similar protections were applied to related plugins such as mysql-logfile and openvpn-client-list to prevent analogous vulnerabilities in other monitoring modules. Organizations running these versions should upgrade immediately to mitigate the risk of unauthorized data exposure through their monitoring infrastructure.