CVE-2023-34256 in Linux
Summary
by MITRE • 05/31/2023
An issue was discovered in the Linux kernel before 6.3.3. There is an out-of-bounds read in crc16 in lib/crc16.c when called from fs/ext4/super.c because ext4_group_desc_csum does not properly check an offset.
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Analysis
by VulDB Data Team • 08/02/2024
The vulnerability identified as CVE-2023-34256 represents a critical out-of-bounds read condition within the Linux kernel version 6.3.2 and earlier. This flaw exists in the crc16 implementation located in lib/crc16.c and is specifically triggered when the function is invoked from fs/ext4/super.c through the ext4_group_desc_csum routine. The issue stems from insufficient validation of offset parameters within the checksum calculation process, creating a scenario where memory access occurs beyond the intended boundaries of allocated buffers.
The technical root cause of this vulnerability lies in the improper bounds checking mechanism within the ext4_group_desc_csum function which is responsible for computing checksums for ext4 filesystem group descriptors. When processing filesystem metadata, the function fails to validate the offset value before using it to index into memory regions containing crc16 data structures. This oversight allows an attacker to manipulate the offset parameter in such a way that subsequent memory accesses reference locations outside the legitimate data boundaries, potentially exposing sensitive kernel memory contents or causing system instability.
This vulnerability falls under the CWE-129 category of Improper Validation of Array Index, which specifically addresses issues where array indices are not properly validated before use. The operational impact of this flaw extends beyond simple memory access violations as it creates potential attack vectors for privilege escalation and information disclosure within the kernel space. An attacker could leverage this vulnerability to read kernel memory contents that should remain protected, potentially extracting sensitive information such as cryptographic keys, passwords, or other confidential data stored in kernel memory regions.
The attack surface for this vulnerability is particularly concerning given that it affects the ext4 filesystem implementation which is widely used across Linux distributions. The out-of-bounds read condition could be exploited through malicious filesystem operations or by crafting specific input data that triggers the vulnerable code path during normal filesystem operations. This makes the vulnerability particularly dangerous as it could be triggered by legitimate system operations rather than requiring specialized attack conditions.
Security professionals should note that this vulnerability aligns with ATT&CK technique T1068 which involves the exploitation of legitimate system processes to gain unauthorized access. The flaw represents a critical kernel-level vulnerability that could enable attackers to extract information from kernel memory or potentially manipulate kernel data structures. Mitigation strategies should focus on updating to kernel versions 6.3.3 or later where the offset validation has been properly implemented. Additionally, system administrators should monitor for any unusual filesystem behavior or memory access patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of rigorous input validation in kernel space code and highlights the critical need for comprehensive testing of cryptographic and checksum routines that handle user-provided or system-generated data within privileged execution contexts.