CVE-2018-14665 in X11 Server
Summary
by MITRE
A flaw was found in xorg-x11-server before 1.20.3. An incorrect permission check for -modulepath and -logfile options when starting Xorg. X server allows unprivileged users with the ability to log in to the system via physical console to escalate their privileges and run arbitrary code under root privileges.
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Analysis
by VulDB Data Team • 08/29/2025
The vulnerability identified as CVE-2018-14665 represents a critical privilege escalation flaw within the xorg-x11-server component of Linux systems, specifically affecting versions prior to 1.20.3. This issue stems from inadequate permission validation mechanisms that govern how the X server processes command-line arguments during initialization. The flaw exists in the handling of two specific options: -modulepath and -logfile, which are critical parameters that control the server's module loading and logging behavior respectively. When these options are improperly validated, they create a pathway for malicious exploitation that directly undermines the security model of the X Window System.
The technical nature of this vulnerability aligns with CWE-284, which addresses improper access control in software systems. The flaw manifests when unprivileged local users who have physical console login access can manipulate the X server startup process to execute arbitrary code with root privileges. This occurs because the X server fails to properly validate the permissions associated with the modulepath and logfile parameters, allowing attackers to specify paths that could be exploited to load malicious modules or redirect logging to locations where they can inject harmful content. The vulnerability exploits the trust relationship between the X server and its configuration parameters, enabling attackers to bypass normal privilege boundaries that should prevent non-root users from executing code with elevated privileges.
From an operational perspective, this vulnerability presents a severe risk to system security as it allows local attackers to achieve root compromise through a relatively simple attack vector. The attack requires only physical console access, which is often available in environments where system administrators might not expect such attacks to occur. Once exploited, the vulnerability provides complete system control, enabling attackers to modify system files, install persistent backdoors, or exfiltrate sensitive data. The impact extends beyond individual systems as compromised X servers can serve as entry points for broader network attacks, particularly in environments where multiple users share physical access to systems or where the X server is configured with permissive security policies.
The attack surface for this vulnerability is particularly concerning given the prevalence of X Window System implementations across various Linux distributions and the typical lack of awareness among users about the security implications of local console access. The exploitability of this flaw is enhanced by the fact that many system administrators do not properly secure console access or implement additional hardening measures that would prevent such privilege escalation. Organizations using affected versions of xorg-x11-server should implement immediate mitigations including updating to version 1.20.3 or later, reviewing console access controls, and implementing additional security measures such as restricting X server startup privileges and monitoring for unauthorized X server modifications. The vulnerability also highlights the importance of proper input validation and privilege separation in system components that handle user-provided parameters, reinforcing the need for comprehensive security testing and validation of all system components that operate with elevated privileges.