CVE-2020-10751 in Linux
Summary
by MITRE
A flaw was found in the Linux kernels SELinux LSM hook implementation before version 5.7, where it incorrectly assumed that an skb would only contain a single netlink message. The hook would incorrectly only validate the first netlink message in the skb and allow or deny the rest of the messages within the skb with the granted permission without further processing.
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Analysis
by VulDB Data Team • 10/19/2020
The vulnerability CVE-2020-10751 represents a critical flaw in the Linux kernel's Security-Enhanced Linux (SELinux) implementation that affects systems running kernel versions prior to 5.7. This issue resides within the Linux Security Module (LSM) framework where SELinux enforces mandatory access controls. The flaw stems from an incorrect assumption in the kernel's network packet processing logic that an skb (socket buffer) contains only a single netlink message. This fundamental misunderstanding creates a significant security gap in the kernel's access control enforcement mechanism.
The technical implementation of this vulnerability occurs in the SELinux LSM hook functions that process network traffic, specifically when handling netlink messages within socket buffers. When multiple netlink messages are bundled together in a single skb, the kernel's validation logic only examines the first message for access control decisions. Subsequent messages within the same skb are processed without additional security validation, potentially allowing unauthorized operations to proceed with the permissions granted to the initial message. This flaw directly violates the principle of least privilege and creates a pathway for privilege escalation or unauthorized access to system resources.
The operational impact of CVE-2020-10751 is substantial as it allows attackers to bypass SELinux access controls in scenarios where multiple netlink messages are transmitted together. This vulnerability can be exploited to perform unauthorized operations within the kernel's security context, potentially leading to privilege escalation, information disclosure, or system compromise. The flaw affects systems that rely on SELinux for mandatory access control, particularly those running older kernel versions that have not been updated to 5.7 or later. Attackers can craft malicious network traffic that includes multiple netlink messages to exploit this bypass mechanism.
Systems affected by this vulnerability include any Linux distribution running kernel versions before 5.7 that utilize SELinux for security policy enforcement. The vulnerability is particularly concerning in enterprise environments where SELinux is actively used to enforce security policies and where systems have not been updated to the patched kernel versions. Organizations running cloud infrastructure, containerized environments, or systems with strict security requirements are at heightened risk. The vulnerability can be exploited remotely through network-based attacks that manipulate netlink message composition within socket buffers.
The remediation strategy for CVE-2020-10751 requires immediate kernel updates to version 5.7 or later where the implementation has been corrected to properly validate all netlink messages within an skb. System administrators should prioritize patching affected systems and verify that SELinux policies remain functional after updates. Organizations should implement network monitoring to detect unusual netlink message patterns that might indicate exploitation attempts. Additionally, security teams should review and audit existing SELinux policies to ensure proper enforcement mechanisms are in place, as this vulnerability demonstrates the importance of robust message validation in kernel security modules.
This vulnerability maps to CWE-119 in the Common Weakness Enumeration catalog, which covers "Improper Restriction of Operations within the Bounds of a Memory Buffer." The flaw demonstrates poor input validation in kernel space operations and represents a classic case of assuming fixed message boundaries in variable-length data structures. From an ATT&CK perspective, this vulnerability aligns with techniques involving privilege escalation and defense evasion, as it allows bypassing mandatory access controls that would normally prevent unauthorized operations within the kernel space. The vulnerability also relates to T1068, which covers 'Local Privilege Escalation', and T1566, covering 'Phishing', as attackers might use network-based delivery methods to exploit this flaw in targeted environments.