CVE-2020-10711 in Linux
Summary
by MITRE
A NULL pointer dereference flaw was found in the Linux kernel's SELinux subsystem in versions before 5.7. This flaw occurs while importing the Commercial IP Security Option (CIPSO) protocol's category bitmap into the SELinux extensible bitmap via the' ebitmap_netlbl_import' routine. While processing the CIPSO restricted bitmap tag in the 'cipso_v4_parsetag_rbm' routine, it sets the security attribute to indicate that the category bitmap is present, even if it has not been allocated. This issue leads to a NULL pointer dereference issue while importing the same category bitmap into SELinux. This flaw allows a remote network user to crash the system kernel, resulting in a denial of service.
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Analysis
by VulDB Data Team • 10/12/2024
The vulnerability identified as CVE-2020-10711 represents a critical NULL pointer dereference flaw within the Linux kernel's Security-Enhanced Linux (SELinux) subsystem, specifically affecting versions prior to 5.7. This issue manifests during the processing of Commercial IP Security Option (CIPSO) protocol category bitmaps, which are used for implementing security labels in network communications. The flaw exists in the interaction between the CIPSO protocol handling and SELinux's extensible bitmap management system, creating a condition where memory allocation validation is bypassed. The vulnerability is particularly concerning as it affects the kernel's core security infrastructure, making it a prime target for exploitation by malicious actors seeking to disrupt system operations.
The technical implementation of this flaw occurs within the ebitmap_netlbl_import routine, which is responsible for importing CIPSO protocol category bitmaps into SELinux's extensible bitmap structures. During processing of the CIPSO restricted bitmap tag through the cipso_v4_parsetag_rbm routine, the system incorrectly sets security attributes to indicate that a category bitmap is present without verifying that the actual memory allocation has occurred. This premature attribute setting creates a scenario where subsequent operations attempt to dereference a NULL pointer, as the system believes the bitmap data exists when it has not been properly allocated in memory. The flaw demonstrates poor input validation and memory management practices that are classified under CWE-476, which specifically addresses NULL pointer dereference vulnerabilities. This type of vulnerability is particularly dangerous in kernel space as it can lead to immediate system crashes and potential privilege escalation opportunities.
The operational impact of CVE-2020-10711 extends beyond simple denial of service, as it represents a fundamental breakdown in kernel security mechanisms that could be exploited to disrupt critical network services. Remote attackers can leverage this vulnerability by sending specially crafted CIPSO protocol packets to systems running vulnerable kernel versions, triggering the NULL pointer dereference and causing the kernel to crash. This results in a complete denial of service condition that affects the entire system, potentially disrupting network connectivity, application availability, and overall system stability. The vulnerability is particularly concerning in environments where network security appliances, firewalls, or systems handling sensitive communications are deployed, as these systems often rely heavily on CIPSO protocol support and SELinux security policies. From an adversarial perspective, this flaw aligns with ATT&CK technique T1499.004, which involves network disruption through kernel-level attacks, and represents a classic example of how protocol handling vulnerabilities can be exploited to achieve system compromise.
Mitigation strategies for CVE-2020-10711 primarily focus on kernel version upgrades to 5.7 or later, which contain the necessary patches to address the NULL pointer dereference issue. System administrators should prioritize updating their kernel versions and ensure that all security patches are applied promptly, especially in environments where network security is critical. Additional defensive measures include implementing network segmentation and access controls to limit exposure to potentially malicious CIPSO protocol traffic, as well as monitoring for unusual network protocol processing patterns that might indicate exploitation attempts. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious CIPSO protocol handling activities, providing early warning capabilities for potential exploitation attempts. The vulnerability serves as a reminder of the importance of thorough input validation and proper memory management in kernel space, particularly for security-critical subsystems like SELinux that handle network protocol data and security labels for system operations.