CVE-2020-8992 in Linux
Summary
by MITRE
ext4_protect_reserved_inode in fs/ext4/block_validity.c in the Linux kernel through 5.5.3 allows attackers to cause a denial of service (soft lockup) via a crafted journal size.
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Analysis
by VulDB Data Team • 03/31/2024
The vulnerability identified as CVE-2020-8992 resides within the Linux kernel's ext4 filesystem implementation, specifically in the ext4_protect_reserved_inode function located in fs/ext4/block_validity.c. This flaw represents a critical denial of service vulnerability that can be exploited by malicious actors to trigger a soft lockup condition, effectively rendering the affected system unresponsive. The vulnerability manifests when attackers manipulate the journal size of an ext4 filesystem in a crafted manner, leading to unexpected behavior in the kernel's block validity checking mechanisms.
The technical root cause of this vulnerability stems from insufficient input validation and boundary checking within the ext4 filesystem's journal handling code. When a maliciously crafted journal size is applied to an ext4 filesystem, the ext4_protect_reserved_inode function fails to properly validate the journal parameters, allowing execution to proceed along an unintended code path. This improper validation leads to a situation where the kernel's block validity checking mechanism becomes trapped in an infinite loop or excessively long-running operation, ultimately causing a soft lockup condition where the system appears frozen but remains technically operational. The vulnerability is classified under CWE-129 as an Improper Validation of Array Index, specifically manifesting as inadequate bounds checking in kernel space code.
The operational impact of this vulnerability extends beyond simple system unresponsiveness, as it can be exploited to create persistent denial of service conditions that are particularly dangerous in production environments. Systems running Linux kernel versions 5.5.3 and earlier are susceptible to this attack, making it a widespread concern across various server and embedded device deployments. The soft lockup condition can affect critical infrastructure components including web servers, database systems, and network appliances that rely on ext4 filesystems. Attackers can leverage this vulnerability to disrupt services without requiring elevated privileges, making it particularly attractive for attackers seeking to cause operational disruption.
Mitigation strategies for CVE-2020-8992 focus primarily on kernel version updates and system hardening measures. The most effective remediation involves upgrading to Linux kernel version 5.6 or later, where the vulnerability has been patched through enhanced input validation and proper boundary checking in the ext4 filesystem code. System administrators should also implement monitoring solutions to detect unusual journal size modifications and establish automated alerting for filesystem anomalies. Network segmentation and access controls can help limit potential exploitation by restricting unauthorized modification of filesystem parameters. The ATT&CK framework categorizes this vulnerability under T1499.004 - Endpoint Denial of Service, as it represents a method for causing system unavailability through kernel-level manipulation. Organizations should also consider implementing filesystem integrity monitoring tools and regular security audits to identify potential exploitation attempts and maintain overall system security posture.