CVE-2016-7949 in libXrender
Summary
by MITRE
Multiple buffer overflows in the (1) XvQueryAdaptors and (2) XvQueryEncodings functions in X.org libXrender before 0.9.10 allow remote X servers to trigger out-of-bounds write operations via vectors involving length fields.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-7949 represents a critical buffer overflow issue affecting the X.org libXrender library version 0.9.9 and earlier. This flaw exists within two specific functions: XvQueryAdaptors and XvQueryEncodings, which are integral components of the X Window System's video extension functionality. The vulnerability stems from insufficient input validation mechanisms that fail to properly sanitize length fields in protocol messages received from remote X servers. These functions process data structures containing length parameters that determine the size of memory allocations and subsequent data copying operations, creating a pathway for malicious actors to manipulate these values and trigger memory corruption. The issue manifests when remote X servers send specially crafted protocol messages containing oversized length fields that exceed the bounds of allocated buffers, leading to out-of-bounds write operations that can result in arbitrary code execution or system instability.
The technical implementation of this vulnerability follows a classic buffer overflow pattern where length fields are used to determine memory allocation sizes without proper bounds checking. When X.org libXrender processes XvQueryAdaptors or XvQueryEncodings requests, it relies on length fields provided by remote servers to allocate memory for response data structures. The absence of validation on these length parameters allows attackers to specify values that cause the application to write data beyond the allocated memory boundaries. This vulnerability directly maps to CWE-121, which describes stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios. The flaw operates at the protocol level within the X11 graphics subsystem, making it particularly dangerous as it can be exploited through network-based attacks against X server implementations that utilize the affected libXrender library. The attack vector requires a remote X server to be accessible, typically through network connections or shared display environments where X11 forwarding is enabled.
The operational impact of CVE-2016-7949 extends beyond simple denial of service conditions, as the out-of-bounds write operations can potentially be leveraged for remote code execution. When exploited successfully, attackers can manipulate memory contents to redirect program execution flow, potentially leading to privilege escalation or complete system compromise. The vulnerability affects systems running X.org libXrender versions prior to 0.9.10, which were commonly found in various Linux distributions, Unix systems, and other operating environments that utilize the X Window System for graphical user interfaces. Organizations relying on X11 forwarding for remote desktop access or X server implementations in networked environments face significant risk exposure. The vulnerability's impact is particularly severe in environments where X11 servers are accessible over untrusted networks or where multiple users share display servers, as it provides a means for remote attackers to gain unauthorized access to systems running vulnerable versions of the library. This weakness can also contribute to broader security incidents when combined with other vulnerabilities in the X11 stack, potentially enabling attackers to establish persistent access or escalate privileges within affected systems.
The mitigation strategy for CVE-2016-7949 centers on upgrading to X.org libXrender version 0.9.10 or later, which includes patches addressing the buffer overflow conditions in both XvQueryAdaptors and XvQueryEncodings functions. System administrators should prioritize patching affected systems, particularly those running X server implementations that may be exposed to remote network access. Additional defensive measures include implementing network segmentation to restrict access to X servers, disabling unnecessary X11 forwarding capabilities, and employing firewall rules to limit X11 protocol traffic. The vulnerability's characteristics align with ATT&CK technique T1059.007, which involves the use of remote services for command execution, and T1210, which covers exploitation of remote services through protocol manipulation. Organizations should also consider implementing intrusion detection systems to monitor for suspicious X11 protocol traffic patterns that may indicate exploitation attempts. Regular vulnerability assessments should target X11 implementations and related libraries to identify other potential buffer overflow conditions that could be exploited in similar fashion. The remediation process should include thorough testing of patched environments to ensure that the updates do not introduce compatibility issues with existing applications that depend on the X11 graphics subsystem.