CVE-2011-4029 in X Server
Summary
by MITRE
The LockServer function in os/utils.c in X.Org xserver before 1.11.2 allows local users to change the permissions of arbitrary files to 444, read those files, and possibly cause a denial of service (removed execution permission) via a symlink attack on a temporary lock file.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/07/2024
The vulnerability described in CVE-2011-4029 represents a critical privilege escalation and file system manipulation issue within the X.Org xserver component. This flaw exists in the LockServer function located in os/utils.c and affects versions prior to 1.11.2, creating a significant security risk for local users who can exploit it to gain unauthorized access to system resources. The vulnerability stems from improper handling of temporary lock files during the server locking process, which creates opportunities for malicious actors to manipulate file permissions and potentially disrupt system operations.
The technical implementation of this vulnerability involves a classic symlink attack pattern where a local user can create a symbolic link to a target file and manipulate the lock file creation process. When the LockServer function attempts to create a temporary lock file, it does not properly validate the file path or ensure that the target is a legitimate lock file rather than a symlink. This allows attackers to redirect the lock file creation to arbitrary locations, subsequently changing permissions of sensitive files to 444, which removes execute permissions and can effectively disable critical system functionality. The vulnerability operates under CWE-59, which specifically addresses improper handling of symbolic links, and represents a direct violation of proper file system access controls.
The operational impact of this vulnerability extends beyond simple permission changes to include potential denial of service conditions and unauthorized data access. By setting file permissions to 444, attackers can effectively prevent execution of critical system binaries or scripts, leading to system instability or complete service disruption. The removal of execute permissions on key system files can cause cascading failures throughout the operating system, particularly affecting services that depend on executable components. Additionally, the ability to read files that would otherwise be protected creates a significant information disclosure risk, as attackers can access sensitive data that should remain restricted to authorized users.
Mitigation strategies for this vulnerability require immediate patching of affected X.Org xserver installations to version 1.11.2 or later, which contains the necessary fixes to properly validate lock file creation and prevent symlink attacks. System administrators should also implement proper file system permissions and access controls, ensuring that temporary directories used by X.Org services have appropriate restrictions to prevent unauthorized file manipulation. The fix addresses the underlying issue by implementing proper validation of file paths and ensuring that lock file creation operations cannot be redirected through symbolic links, thereby preventing the privilege escalation and file manipulation capabilities that make this vulnerability so dangerous. Organizations should also consider implementing monitoring for suspicious file system activity and access patterns that could indicate exploitation attempts, as this vulnerability falls under ATT&CK technique T1068 which covers exploit for privilege escalation and T1070 which covers indicator removal through file deletion or modification.