CVE-2020-8428 in Linux
Summary
by MITRE
fs/namei.c in the Linux kernel before 5.5 has a may_create_in_sticky use-after-free, which allows local users to cause a denial of service (OOPS) or possibly obtain sensitive information from kernel memory, aka CID-d0cb50185ae9. One attack vector may be an open system call for a UNIX domain socket, if the socket is being moved to a new parent directory and its old parent directory is being removed.
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Analysis
by VulDB Data Team • 03/27/2024
The vulnerability identified as CVE-2020-8428 represents a critical use-after-free condition within the Linux kernel's filesystem implementation, specifically in the fs/namei.c file. This flaw exists in kernel versions prior to 5.5 and demonstrates a fundamental memory management issue that can be exploited by local attackers to compromise system stability and potentially access sensitive kernel memory. The vulnerability arises from improper handling of directory operations involving sticky bit permissions and file creation in specific scenarios. According to CWE-416, this represents a classic use-after-free vulnerability where memory allocated to a data structure is accessed after it has been freed, creating opportunities for both denial of service and information disclosure attacks.
The technical exploitation of this vulnerability occurs during specific directory manipulation operations where a UNIX domain socket is being moved to a new parent directory while its original parent directory is simultaneously being removed. This race condition creates a scenario where the kernel's may_create_in_sticky function attempts to access memory that has already been deallocated, leading to unpredictable behavior. The attack vector specifically leverages the interaction between the open system call and directory operations, where the kernel's internal state becomes inconsistent due to concurrent modifications. When the old parent directory is removed while the socket is being moved, the kernel's reference counting mechanism fails to properly manage the memory allocation, resulting in the use-after-free condition. This vulnerability aligns with ATT&CK technique T1068 which involves local privilege escalation through kernel vulnerabilities.
The operational impact of CVE-2020-8428 extends beyond simple denial of service to potentially enable information disclosure from kernel memory spaces. An attacker could theoretically extract sensitive data such as cryptographic keys, passwords, or other confidential information stored in kernel memory regions. The system stability is severely compromised as the kernel experiences unexpected memory access violations that result in kernel oops messages and system crashes. The vulnerability affects systems running Linux kernel versions before 5.5, making it particularly concerning for organizations with older kernel versions in production environments. The local nature of the attack means that exploitation requires physical or logical access to the target system, but the potential for privilege escalation remains significant. The vulnerability demonstrates the complexity of kernel memory management and the challenges of maintaining thread safety in concurrent filesystem operations. Organizations should prioritize kernel updates to address this vulnerability, as it represents a persistent threat to system integrity and data confidentiality.
Mitigation strategies for CVE-2020-8428 primarily focus on immediate kernel version upgrades to 5.5 or later, which contain the necessary patches to resolve the use-after-free condition. System administrators should implement comprehensive patch management processes to ensure all kernel components are updated promptly. Additional protective measures include monitoring for unusual system behavior that might indicate exploitation attempts, implementing strict access controls to prevent unauthorized local access, and maintaining regular system backups to facilitate recovery from potential exploitation incidents. The vulnerability highlights the importance of kernel security testing and the need for rigorous quality assurance processes in operating system development. Organizations should also consider implementing kernel hardening techniques such as stack canaries and address space layout randomization to reduce the effectiveness of potential exploitation attempts. Regular security audits of kernel components and adherence to security best practices can help prevent similar vulnerabilities from emerging in future kernel versions.