CVE-2020-28097 in Linux
Summary
by MITRE • 06/24/2021
The vgacon subsystem in the Linux kernel before 5.8.10 mishandles software scrollback. There is a vgacon_scrolldelta out-of-bounds read, aka CID-973c096f6a85.
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Analysis
by VulDB Data Team • 06/26/2021
The vulnerability identified as CVE-2020-28097 resides within the vgacon subsystem of the Linux kernel, specifically affecting versions prior to 5.8.10. This subsystem is responsible for managing VGA console output and handling software scrollback functionality, which allows users to navigate through previously displayed console text. The issue manifests as an out-of-bounds read condition that occurs when processing scrollback operations, representing a critical flaw in kernel memory management and input validation.
The technical flaw stems from improper bounds checking within the vgacon_scrolldelta function, which handles scrollback delta operations for VGA console devices. When a user or application performs scrollback operations, the kernel fails to properly validate the boundary conditions of memory accesses, leading to a situation where the code attempts to read memory locations beyond the allocated buffer boundaries. This vulnerability falls under CWE-129, which describes improper validation of array indices, and specifically relates to improper bounds checking in kernel space operations. The out-of-bounds read can potentially expose sensitive kernel memory contents, including stack contents, kernel data structures, or other confidential information that may be accessible through the memory access pattern.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential pathways for privilege escalation and system compromise. An attacker who can trigger the vulnerable code path may be able to extract kernel memory contents, which could reveal critical information such as stack canaries, kernel pointers, or other sensitive data structures. This information could then be leveraged to perform more sophisticated attacks including bypassing kernel address space layout randomization or exploiting other vulnerabilities in the kernel. The vulnerability is particularly concerning in environments where unprivileged users have access to console devices or where applications can interact with VGA console subsystems, as it represents a potential attack vector for local privilege escalation.
Mitigation strategies for CVE-2020-28097 primarily involve upgrading to Linux kernel version 5.8.10 or later, where the bounds checking has been properly implemented to prevent the out-of-bounds read condition. System administrators should prioritize patching affected systems, particularly those running older kernel versions where the vulnerability exists. Additionally, implementing proper access controls to limit user interaction with VGA console subsystems can reduce the attack surface. The vulnerability aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation', and T1005, 'Data from Local System', as it enables potential data extraction from kernel memory. Organizations should also consider monitoring for unusual console scrollback operations or memory access patterns that might indicate exploitation attempts, and ensure comprehensive testing of kernel updates to prevent regression issues in production environments.