CVE-2019-11833 in Linux
Summary
by MITRE
fs/ext4/extents.c in the Linux kernel through 5.1.2 does not zero out the unused memory region in the extent tree block, which might allow local users to obtain sensitive information by reading uninitialized data in the filesystem.
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Analysis
by VulDB Data Team • 09/19/2023
The vulnerability identified as CVE-2019-11833 resides within the ext4 filesystem implementation of the Linux kernel, specifically in the fs/ext4/extents.c file. This flaw represents a classic case of information disclosure through uninitialized memory access, where the kernel fails to properly sanitize memory regions during filesystem operations. The vulnerability affects Linux kernel versions through 5.1.2, making it a significant concern for systems running these kernel versions. The issue manifests when the extent tree block structure is manipulated, creating a scenario where sensitive data from previous operations might persist in memory regions that are subsequently exposed to userspace applications.
The technical root cause of this vulnerability stems from the kernel's failure to zero out unused memory regions within the extent tree block structure. When ext4 manages file system extents, it allocates memory blocks to store metadata about file locations and sizes. However, during certain operations such as extent insertion or modification, the kernel does not properly clear memory regions that are no longer actively used within the extent tree. This creates a situation where data from previous filesystem operations, potentially including sensitive information from other processes or system components, remains accessible in memory. The vulnerability is particularly concerning because it operates at the kernel level where such information disclosure can expose critical system data, including credentials, encryption keys, or other confidential information.
From an operational impact perspective, this vulnerability enables local users to obtain sensitive information through reading uninitialized data in the filesystem. Attackers could potentially exploit this by creating specific filesystem operations that cause the kernel to expose memory regions containing previously stored data. The attack vector is particularly dangerous because it requires only local access to the system, making it more accessible than many other kernel vulnerabilities. The information disclosure could potentially include process memory contents, kernel data structures, or other sensitive information that might aid in further exploitation attempts. This vulnerability aligns with CWE-119, which addresses improper access to memory locations, and represents a form of information disclosure that can be leveraged for privilege escalation or data theft.
The security implications of CVE-2019-11833 extend beyond simple information disclosure, as the leaked data could potentially contain cryptographic keys, authentication tokens, or other sensitive system information. The vulnerability's classification under ATT&CK technique T1005 suggests it could be used for data collection activities, while its kernel-level nature makes it particularly dangerous for systems with high security requirements. Systems running affected kernel versions are vulnerable to attacks that could compromise data confidentiality and potentially lead to more severe security breaches. Organizations should prioritize patching this vulnerability, as the exposure of uninitialized memory data creates a significant risk for systems handling sensitive information. The vulnerability demonstrates the critical importance of proper memory management in kernel code and highlights the potential for seemingly benign memory handling issues to create serious security risks.
Mitigation strategies for this vulnerability primarily involve upgrading to a patched kernel version where the memory zeroing behavior has been corrected. System administrators should implement immediate patching procedures to address this vulnerability, as the risk of exploitation increases with the amount of time systems remain unpatched. Additionally, monitoring for unusual filesystem operations that might trigger memory exposure scenarios can help detect potential exploitation attempts. The fix implemented in patched versions typically involves ensuring that memory regions within the extent tree blocks are properly zeroed before being made available for reuse, preventing the exposure of stale data. Organizations should also consider implementing additional security controls such as mandatory access controls and process isolation to limit the potential impact of any successful exploitation attempts.