CVE-2020-14331 in Linux
Summary
by MITRE
A flaw was found in the Linux kernel’s implementation of the invert video code on VGA consoles when a local attacker attempts to resize the console, calling an ioctl VT_RESIZE, which causes an out-of-bounds write to occur. This flaw allows a local user with access to the VGA console to crash the system, potentially escalating their privileges on the system. 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 • 09/16/2020
The vulnerability identified as CVE-2020-14331 represents a critical out-of-bounds write flaw within the Linux kernel's VGA console implementation that manifests during console resizing operations. This issue specifically affects the invert video code functionality when a local attacker executes a VT_RESIZE ioctl command to modify console dimensions. The flaw exists in the kernel's handling of video console operations and demonstrates how seemingly benign administrative functions can become attack vectors when proper bounds checking mechanisms fail. The vulnerability resides in the kernel's console subsystem where it processes terminal resize requests without adequate validation of input parameters, creating a pathway for malicious code execution.
The technical exploitation of this vulnerability occurs through the manipulation of VGA console resize operations using the VT_RESIZE ioctl interface which is designed to adjust terminal dimensions. When an attacker invokes this ioctl function with malformed parameters, the kernel's invert video code implementation fails to properly validate the console size parameters, leading to memory corruption through out-of-bounds writes. This memory corruption directly impacts kernel memory structures and can result in immediate system crashes or more subtle privilege escalation opportunities. The vulnerability's classification as a local privilege escalation vector stems from the fact that attackers with access to the VGA console can leverage this flaw to potentially elevate their privileges, making it particularly dangerous in multi-user environments where console access might be available to untrusted users.
The operational impact of CVE-2020-14331 extends beyond simple system crashes to encompass data integrity and confidentiality risks as well as complete system availability compromise. System administrators face the challenge of maintaining stable operations when this vulnerability is present, as the out-of-bounds write can corrupt kernel memory structures and cause unpredictable behavior. The vulnerability's potential for privilege escalation creates additional security concerns where an attacker could gain elevated system privileges and access sensitive data or system resources. Organizations running Linux systems with VGA console access must consider this flaw as a critical threat that could lead to complete system compromise, particularly in environments where console access is not properly restricted or monitored.
Mitigation strategies for CVE-2020-14331 should focus on immediate kernel updates from vendors such as Red Hat, SUSE, and Canonical, which have released patches addressing the specific out-of-bounds write vulnerability in the VGA console implementation. System administrators should implement access controls to restrict console access and monitor for unauthorized VT_RESIZE operations, as this vulnerability requires local access to exploit effectively. The implementation of kernel hardening measures such as stack canaries and address space layout randomization can provide additional protection layers against exploitation attempts. Security monitoring solutions should be configured to detect suspicious ioctl operations targeting the VGA console, particularly VT_RESIZE calls that might indicate exploitation attempts. Organizations should also consider implementing privilege separation mechanisms to limit user access to console operations and ensure that only trusted users have access to VGA console functionality that could be exploited through this vulnerability. The vulnerability aligns with CWE-121 and CWE-125 categories related to buffer overflow conditions and out-of-bounds memory access, and represents a potential pathway for techniques described in the ATT&CK framework under privilege escalation and defense evasion tactics.