CVE-2015-5199 in libvdpau
Summary
by MITRE
Directory traversal vulnerability in dlopen in libvdpau before 1.1.1 allows local users to gain privileges via the VDPAU_DRIVER environment variable.
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Analysis
by VulDB Data Team • 02/01/2019
The vulnerability identified as CVE-2015-5199 represents a directory traversal flaw within the dynamic loading mechanism of the Video Decode and Presentation API for Unix (VDPAU) library. This issue affects versions of libvdpau prior to 1.1.1 and specifically targets the dlopen function implementation. The vulnerability manifests through manipulation of the VDPAU_DRIVER environment variable, which is used by applications to specify which graphics driver library should be loaded for hardware-accelerated video decoding and presentation. The flaw allows local attackers to craft malicious paths that can bypass normal file access restrictions and potentially load arbitrary shared libraries from unexpected locations.
The technical exploitation of this vulnerability occurs because the VDPAU library does not properly validate or sanitize the VDPAU_DRIVER environment variable before passing it to the dlopen function. When an application sets this environment variable to a crafted path containing directory traversal sequences such as "../", the library may resolve these paths to locations outside of the intended driver directories. This improper input validation creates an opportunity for privilege escalation attacks where an attacker can load malicious shared libraries with elevated privileges. The vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and represents a classic path traversal attack vector that has been commonly exploited in various software components over the years.
The operational impact of CVE-2015-5199 extends beyond simple local privilege escalation to potentially compromise the entire graphics subsystem of affected systems. Since VDPAU is commonly used in multimedia applications, video players, and desktop environments, an attacker who successfully exploits this vulnerability can gain elevated privileges to execute arbitrary code with the permissions of the target process. This is particularly concerning in multi-user environments where local users might exploit the vulnerability to elevate their privileges to those of the graphics subsystem or even root access. The attack requires local system access, making it a local privilege escalation vulnerability that falls under the ATT&CK technique T1068, which covers local privilege escalation through exploitation of software vulnerabilities. The vulnerability is especially dangerous because it leverages legitimate system functionality to achieve its malicious objectives, making detection more challenging.
Mitigation strategies for CVE-2015-5199 primarily involve updating to libvdpau version 1.1.1 or later, which contains the necessary patches to properly validate the VDPAU_DRIVER environment variable. System administrators should also implement proper environment variable sanitization at the application level by validating and restricting paths before they are passed to dlopen functions. Additional protective measures include restricting write permissions to directories containing graphics drivers and implementing runtime monitoring to detect suspicious library loading patterns. Organizations should also consider implementing the principle of least privilege for graphics-related processes and regularly audit their VDPAU configurations to ensure that environment variables are not being set to potentially malicious values. The vulnerability serves as a reminder of the importance of proper input validation in dynamic loading functions and demonstrates how seemingly benign environment variables can become attack vectors when not properly sanitized.