CVE-2011-3153 in LightDM
Summary
by MITRE
dmrc.c in Light Display Manager (aka LightDM) before 1.1.1 allows local users to read arbitrary files via a symlink attack on ~/.dmrc.
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Analysis
by VulDB Data Team • 05/07/2026
The vulnerability identified as CVE-2011-3153 affects Light Display Manager version 1.1.0 and earlier, representing a critical security flaw in the desktop environment's handling of user configuration files. This issue specifically resides in the dmrc.c component which processes the ~/.dmrc file, a configuration file used by LightDM to store user session preferences and display settings. The vulnerability stems from improper handling of symbolic links during file access operations, creating a path traversal condition that allows malicious local users to bypass normal file access controls. The flaw enables attackers to read arbitrary files on the system by exploiting a race condition or direct symlink manipulation within the user's home directory.
The technical implementation of this vulnerability involves the manipulation of the ~/.dmrc file through symbolic link attacks, where an attacker creates a symbolic link pointing to a sensitive system file instead of the legitimate configuration file. This type of attack falls under the category of insecure file handling practices and aligns with CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities. The flaw demonstrates a classic privilege escalation vector where local users can gain unauthorized access to files they would normally not be able to read, potentially exposing sensitive information such as user credentials, session data, or system configuration details.
The operational impact of CVE-2011-3153 extends beyond simple information disclosure, as it represents a fundamental weakness in the desktop environment's security model. Attackers can leverage this vulnerability to read system files that contain sensitive data, potentially leading to further exploitation opportunities including credential theft, privilege escalation, or information gathering for more sophisticated attacks. The vulnerability affects all systems running LightDM versions prior to 1.1.1, making it particularly concerning for desktop environments where multiple users may share a system. This flaw represents a breach in the principle of least privilege, allowing local users to circumvent normal file access controls that should protect sensitive system resources.
Mitigation strategies for this vulnerability require immediate patching of LightDM to version 1.1.1 or later, which addresses the symlink handling issue through proper file access validation and atomic file operations. System administrators should implement proper file permissions and ownership checks to prevent unauthorized symlink creation in user directories. The fix typically involves implementing proper input validation and ensuring that file operations occur in a secure manner that prevents race conditions between file checks and actual file access. Organizations should also consider implementing monitoring for suspicious symlink creation activities and ensure that user home directories maintain appropriate security controls. This vulnerability highlights the importance of secure coding practices in desktop environments and the need for proper file handling mechanisms that prevent TOCTOU race conditions. The remediation process should include comprehensive testing to ensure that the patched version properly handles all file access scenarios without reintroducing similar vulnerabilities. Additionally, system hardening measures should be implemented to restrict user capabilities in creating symbolic links in sensitive directories, aligning with security best practices recommended by organizations such as the Center for Internet Security and NIST guidelines for secure system configuration.