CVE-2007-4730 in X11
Summary
by MITRE
Buffer overflow in the compNewPixmap function in compalloc.c in the Composite extension for the X.org X11 server before 1.4 allows local users to execute arbitrary code by copying data from a large pixel depth pixmap into a smaller pixel depth pixmap.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability identified as CVE-2007-4730 represents a critical buffer overflow flaw within the X.org X11 server's Composite extension, specifically within the compNewPixmap function located in compalloc.c. This issue affects X11 server versions prior to 1.4 and creates a significant security risk for local users who can exploit it to execute arbitrary code on affected systems. The flaw occurs during the process of copying pixel data between pixmap objects with different depth specifications, creating a scenario where insufficient bounds checking allows memory corruption to occur.
The technical implementation of this vulnerability stems from improper handling of pixmap data transfer operations where the composite extension fails to validate the dimensions and memory requirements when copying data from a high-depth pixmap to a low-depth pixmap. When the compNewPixmap function processes such operations, it does not adequately verify that the destination buffer has sufficient capacity to accommodate the source data, leading to a classic buffer overflow condition. This memory corruption can be leveraged by malicious local users to overwrite adjacent memory locations, potentially corrupting program execution flow and enabling code execution with the privileges of the X server process.
The operational impact of CVE-2007-4730 extends beyond simple local privilege escalation as it can compromise the entire graphical session and potentially provide attackers with elevated system access. Since the X11 server typically runs with elevated privileges to manage graphics hardware and display resources, exploitation of this vulnerability can result in complete system compromise. The attack vector requires local access to the system, making it particularly dangerous in multi-user environments where users may have legitimate access to X11 sessions but could leverage this flaw for unauthorized code execution. This vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates how improper memory management in graphics subsystems can create persistent security risks.
Mitigation strategies for CVE-2007-4730 primarily focus on upgrading to X.org X11 server version 1.4 or later, where the buffer overflow has been addressed through proper bounds checking and memory validation procedures. System administrators should also implement additional security measures including restricting local user access to X11 sessions where possible, employing mandatory access controls such as SELinux or AppArmor, and monitoring for suspicious X11 activity that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper memory management in graphics libraries and highlights how seemingly benign operations like pixmap copying can create significant security risks when proper input validation is absent. Organizations should also consider implementing network segmentation to limit access to systems running X11 servers and ensure that all X11 components are regularly updated to prevent exploitation of known vulnerabilities. This flaw serves as a reminder of the critical security considerations required in graphics subsystem implementations and the potential for local privilege escalation through improper memory handling in system-level components.