CVE-2021-4011 in X11
Summary
by MITRE • 12/17/2021
A flaw was found in xorg-x11-server in versions before 21.1.2 and before 1.20.14. An out-of-bounds access can occur in the SwapCreateRegister function. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
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Analysis
by VulDB Data Team • 10/01/2025
The vulnerability identified as CVE-2021-4011 affects the xorg-x11-server component of Linux systems, specifically impacting versions prior to 21.1.2 and 1.20.14. This flaw exists within the SwapCreateRegister function, which is part of the X Window System server implementation responsible for managing graphics rendering and display operations. The issue manifests as an out-of-bounds memory access condition that can be exploited by malicious actors to compromise system stability and security. The vulnerability is categorized under CWE-125, which represents an out-of-bounds read condition, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The affected system components include the X11 server's graphics subsystem, which handles window management, display rendering, and graphics operations for graphical user interfaces.
The technical implementation of this vulnerability occurs when the SwapCreateRegister function processes certain input parameters without proper bounds checking. When malicious input is provided to this function, it can cause the system to access memory locations outside the intended buffer boundaries. This out-of-bounds access can result in memory corruption, leading to unpredictable behavior including application crashes, system instability, and potential privilege escalation. The vulnerability's impact extends beyond simple system crashes as it can be leveraged to extract sensitive information from memory through information disclosure attacks, thereby compromising data confidentiality and integrity. The flaw essentially allows an attacker to manipulate the graphics server's memory management routines, potentially enabling more sophisticated attacks against the underlying system.
From an operational perspective, this vulnerability poses significant risks to system availability and overall security posture. An attacker who successfully exploits this vulnerability can cause denial of service conditions that prevent legitimate users from accessing graphical interfaces and system resources. The impact on data confidentiality is particularly concerning as memory corruption can potentially expose sensitive information stored in adjacent memory regions, including authentication credentials, system configuration data, and user information. The integrity implications extend to the possibility of arbitrary code execution, which could allow attackers to gain elevated privileges and establish persistent access to affected systems. This vulnerability affects systems running graphical environments including desktop workstations, servers with GUI interfaces, and any system utilizing the X Window System for display management.
Mitigation strategies for CVE-2021-4011 primarily focus on updating the xorg-x11-server package to versions 21.1.2 or 1.20.14, which contain the necessary patches to address the out-of-bounds access condition. System administrators should prioritize patching all affected systems, particularly those with exposed graphical interfaces or remote access capabilities. Additional protective measures include implementing network segmentation to limit access to systems running X11 servers, disabling unnecessary graphical services, and monitoring for suspicious activity related to graphics server operations. Security teams should also consider implementing intrusion detection systems that can identify potential exploitation attempts targeting the SwapCreateRegister function. The vulnerability's classification under ATT&CK framework as a denial of service and information disclosure threat emphasizes the need for comprehensive monitoring and incident response procedures. Organizations should conduct vulnerability assessments to identify all systems running affected versions of the X11 server and implement proper access controls to minimize the attack surface. Regular security updates and patch management programs are essential to prevent exploitation of similar vulnerabilities in the graphics subsystem.