CVE-2016-7953 in libXvMC
Summary
by MITRE
Buffer underflow in X.org libXvMC before 1.0.10 allows remote X servers to have unspecified impact via an empty string.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-7953 represents a critical buffer underflow flaw within the X.org libXvMC library version 1.0.9 and earlier. This library serves as a crucial component for hardware-accelerated video decoding in X Window System environments, particularly supporting MPEG-2 and other video formats through the X Video Extension framework. The flaw manifests when the library processes video data containing empty strings, creating a condition where memory access occurs beyond the allocated buffer boundaries. This type of vulnerability falls under the CWE-121 category of Buffer Underflow, which is classified as a serious weakness in memory management and input validation.
The technical implementation of this vulnerability occurs within the XvMC library's handling of video stream data processing. When a remote X server sends video data containing empty strings as part of the video frame metadata, the libXvMC library fails to properly validate the input length before performing memory operations. This leads to a situation where the application attempts to read or write data at memory locations preceding the allocated buffer, potentially corrupting adjacent memory regions and creating opportunities for arbitrary code execution or system instability. The unspecified impact mentioned in the CVE description indicates that the consequences could range from denial of service to complete system compromise depending on the specific execution environment and memory layout.
The operational impact of this vulnerability extends across numerous X Window System implementations and affects systems running affected versions of the X.org server stack. Any system utilizing hardware-accelerated video decoding through libXvMC becomes potentially vulnerable to remote exploitation by malicious X servers. This includes desktop environments, server installations, and embedded systems that rely on X11 for graphics rendering. The vulnerability is particularly concerning because it operates at the graphics subsystem level, potentially allowing attackers to compromise the entire graphical environment or even escalate privileges to gain deeper system access. According to ATT&CK framework, this vulnerability maps to T1059.007 for remote code execution capabilities and T1499.004 for denial of service scenarios.
Mitigation strategies for CVE-2016-7953 primarily focus on updating the affected libXvMC library to version 1.0.10 or later, which includes proper input validation and buffer boundary checks. System administrators should prioritize patching all affected X.org installations, particularly those running in networked environments where remote X server access is possible. Additional protective measures include implementing network segmentation to restrict X server access, configuring X11 access controls through xhost and xauth mechanisms, and monitoring for unusual X server activity patterns. The vulnerability demonstrates the importance of robust input validation in graphics libraries and highlights the need for comprehensive security testing of hardware acceleration components. Organizations should also consider implementing intrusion detection systems to monitor for potential exploitation attempts targeting X11-based vulnerabilities, as these attacks often occur through network-based X server connections.