CVE-2021-3472 in xorg-x11-server
Summary
by MITRE • 04/26/2021
A flaw was found in xorg-x11-server in versions before 1.20.11. An integer underflow can occur in xserver which can lead to a local privilege escalation. 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 • 05/02/2021
The vulnerability identified as CVE-2021-3472 resides within the xorg-x11-server component of Linux systems, specifically affecting versions prior to 1.20.11. This flaw represents a critical security weakness that stems from improper input validation mechanisms within the X Window System server implementation. The issue manifests as an integer underflow condition that can be exploited by local attackers to escalate their privileges from standard user level to root access. The vulnerability is particularly concerning because it operates at the core system level where graphical server processes run, making it a prime target for privilege escalation attacks that could compromise entire system operations.
The technical exploitation of this vulnerability occurs through a specific code path within the xserver component where integer arithmetic operations fail to properly validate input parameters. When malicious input is processed by the server, it triggers an integer underflow condition that can result in memory corruption and arbitrary code execution. This flaw falls under the CWE-191 category of Integer Underflow or Wraparound, which is classified as a common weakness in software security practices. The underlying mechanism involves the server's handling of certain protocol messages or configuration parameters that are expected to be within specific numerical ranges but can be manipulated to cause the arithmetic overflow condition.
The operational impact of CVE-2021-3472 extends beyond simple privilege escalation to encompass broader system compromise capabilities. Attackers who successfully exploit this vulnerability can gain root access to affected systems, potentially leading to complete system takeover and unauthorized access to sensitive data. The threat model for this vulnerability aligns with ATT&CK technique T1068 which covers 'Exploitation for Privilege Escalation' and T1547.001 which covers 'Registry Run Keys / Startup Folder'. The compromise of system availability is particularly significant as attackers can manipulate the X server to cause denial of service conditions while simultaneously maintaining persistent access to the compromised system.
System confidentiality and integrity are severely compromised through this vulnerability since local privilege escalation allows attackers to access all system resources, modify critical files, and potentially exfiltrate sensitive data. The vulnerability affects systems that rely on X11 graphical environments, which is common across desktop and server deployments in enterprise environments. Organizations using affected versions of xorg-x11-server face significant risk exposure, particularly in environments where local users have access to graphical interfaces or where system administrators may be running graphical applications with elevated privileges. The exploitation requires local access but does not require network connectivity, making it particularly dangerous in multi-user environments where privilege separation is expected.
Mitigation strategies for CVE-2021-3472 primarily focus on immediate version updates to xorg-x11-server 1.20.11 or later, which contain the necessary patches to address the integer underflow condition. System administrators should prioritize patching affected systems and implementing proper access controls to limit local user privileges where possible. Additional security measures include monitoring for suspicious X server processes, implementing intrusion detection systems that can identify exploitation attempts, and maintaining comprehensive system logging to detect unauthorized privilege escalation activities. The vulnerability demonstrates the importance of proper input validation and arithmetic overflow protection in system-level software components, aligning with security best practices outlined in NIST SP 800-144 and ISO/IEC 27001 security frameworks. Organizations should also consider implementing least privilege principles and regular security assessments to identify similar vulnerabilities in other system components that may be susceptible to similar integer overflow conditions.