CVE-2021-4010 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 SProcScreenSaverSuspend function. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 12/24/2021
The vulnerability identified as CVE-2021-4010 represents a critical out-of-bounds memory access flaw within the xorg-x11-server component of Linux systems. This issue affects versions prior to 21.1.2 and 1.20.14, making it a widespread concern across numerous Linux distributions that rely on the X Window System for graphical user interfaces. The flaw specifically manifests in the SProcScreenSaverSuspend function, which handles screen saver suspension operations within the X server environment. The vulnerability arises from insufficient input validation and boundary checking within this particular function, creating an exploitable condition that can be leveraged by malicious actors to disrupt normal system operations.
The technical nature of this vulnerability places it squarely within the realm of CWE-129, which addresses insufficient input validation, and more specifically relates to CWE-787, representing out-of-bounds write operations. The SProcScreenSaverSuspend function fails to properly validate array indices or buffer boundaries when processing screen saver suspension requests, allowing attackers to craft malicious input that triggers memory access violations. This type of vulnerability can be particularly dangerous because it operates within the core graphics server component that many applications depend upon for display functionality. The out-of-bounds access can potentially lead to memory corruption, which may result in arbitrary code execution or system crashes depending on the specific circumstances of exploitation.
From an operational impact perspective, this vulnerability poses significant threats to data confidentiality, integrity, and system availability as indicated in the original description. The compromise of system availability represents the most immediate concern, as successful exploitation could lead to denial-of-service conditions where the X server crashes or becomes unresponsive, effectively rendering graphical user interfaces inaccessible to users. Data integrity threats emerge from potential memory corruption that could affect application data or system state, while confidentiality risks arise from the possibility of information disclosure through memory leaks or side-channel attacks. The vulnerability's exploitation could be particularly damaging in enterprise environments where graphical interfaces are critical for system administration and user productivity, potentially leading to widespread service disruption.
The attack surface for this vulnerability extends across various attack vectors including local privilege escalation scenarios and potentially remote exploitation if the X server is configured to accept network connections. According to ATT&CK framework, this vulnerability could be categorized under T1068 for local privilege escalation and T1499 for network denial-of-service attacks. Mitigation strategies should focus on immediate patching of affected systems to version 21.1.2 or 1.20.14, which contain the necessary fixes for the boundary checking issues. System administrators should also implement network segmentation to limit access to X server components, disable unnecessary X11 forwarding capabilities, and monitor for suspicious activity related to screen saver operations. Additionally, implementing proper input validation controls and memory safety checks in the affected functions can provide additional layers of protection against similar vulnerabilities in the future, aligning with security best practices outlined in the OWASP Top 10 and NIST cybersecurity frameworks.