CVE-2019-19767 in Linux
Summary
by MITRE
The Linux kernel before 5.4.2 mishandles ext4_expand_extra_isize, as demonstrated by use-after-free errors in __ext4_expand_extra_isize and ext4_xattr_set_entry, related to fs/ext4/inode.c and fs/ext4/super.c, aka CID-4ea99936a163.
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Analysis
by VulDB Data Team • 08/10/2025
The vulnerability described in CVE-2019-19767 represents a critical use-after-free condition within the Linux kernel's ext4 filesystem implementation that affects versions prior to 5.4.2. This flaw manifests in the ext4_expand_extra_isize function and its associated helper functions __ext4_expand_extra_isize and ext4_xattr_set_entry, which are located in the filesystem's inode.c and super.c source files. The issue arises from improper memory management during extended attribute operations on ext4 filesystems, creating a scenario where freed memory locations are accessed after the original allocation has been released, leading to potential system instability and security exploitation.
The technical exploitation of this vulnerability occurs when an attacker manipulates extended attributes on files within an ext4 filesystem, triggering the flawed memory handling logic. The use-after-free condition specifically emerges during the expansion of extra inode space, where the kernel fails to properly validate or manage memory references after certain operations have been completed. This memory corruption vulnerability can be leveraged to execute arbitrary code with kernel privileges, as the freed memory may be reallocated for other purposes while the original code path still attempts to access it. The flaw is particularly dangerous because it operates at the kernel level, allowing attackers to bypass user-space protections and potentially gain complete system control.
From an operational impact perspective, this vulnerability poses significant risks to systems running affected Linux kernel versions, particularly those that rely heavily on ext4 filesystems for storage operations. The use-after-free condition can lead to system crashes, data corruption, or unauthorized privilege escalation, making it a critical concern for enterprise environments, cloud infrastructure, and any system where kernel-level stability is paramount. The vulnerability affects not only individual systems but also broader network infrastructures, as compromised systems can serve as entry points for further attacks. Organizations using older kernel versions without proper patching are particularly vulnerable to exploitation attempts, as the flaw exists in the core filesystem handling mechanisms that are fundamental to system operation.
Mitigation strategies for CVE-2019-19767 primarily focus on immediate kernel version upgrades to 5.4.2 or later, which contain the necessary patches to address the memory management issues in ext4 filesystem operations. System administrators should prioritize patching across all affected environments, particularly in production systems where the risk of exploitation is highest. Additionally, implementing proper access controls and monitoring for unusual filesystem operations can help detect potential exploitation attempts. The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions, and represents a classic example of how memory management flaws in kernel code can create severe security implications. Organizations should also consider implementing the principle of least privilege and maintaining robust backup and recovery procedures to mitigate potential impact from exploitation attempts. This vulnerability demonstrates the critical importance of timely kernel updates and proper security maintenance practices in protecting against sophisticated attacks targeting core operating system components.