CVE-2023-0459 in Linux
Summary
by MITRE • 05/25/2023
Copy_from_user on 64-bit versions of the Linux kernel does not implement the __uaccess_begin_nospec allowing a user to bypass the "access_ok" check and pass a kernel pointer to copy_from_user(). This would allow an attacker to leak information. We recommend upgrading beyond commit 74e19ef0ff8061ef55957c3abd71614ef0f42f47
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Analysis
by VulDB Data Team • 06/10/2023
The vulnerability identified as CVE-2023-0459 represents a critical flaw in the Linux kernel's memory management subsystem that specifically affects 64-bit architectures. This issue stems from an improper implementation of user space memory access validation mechanisms within the kernel's copy_from_user function. The vulnerability occurs when the kernel fails to properly execute the __uaccess_begin_nospec instrumentation that should prevent speculative execution attacks against kernel memory regions. This oversight creates a pathway for malicious user-space processes to bypass essential access validation checks that are designed to protect kernel memory from unauthorized access.
The technical root cause of this vulnerability lies in the failure to properly implement the uaccess instrumentation framework that is fundamental to kernel security. When copy_from_user is called on 64-bit systems, the absence of __uaccess_begin_nospec means that the kernel's access_ok check can be bypassed through carefully crafted user-space inputs. This allows an attacker to pass kernel virtual addresses directly to the copy_from_user function, effectively creating a mechanism for information disclosure. The vulnerability specifically affects the kernel's ability to validate memory access permissions during user-to-kernel data transfers, enabling a class of attacks that leverage speculative execution to leak kernel memory contents.
The operational impact of this vulnerability is severe as it provides attackers with a means to perform information leakage attacks against running kernel processes. An attacker who can successfully exploit this vulnerability can potentially extract sensitive kernel memory contents including cryptographic keys, passwords, and other confidential data stored in kernel memory regions. This type of information disclosure can serve as a foundation for more sophisticated attacks, including privilege escalation or further exploitation of other kernel vulnerabilities. The vulnerability is particularly dangerous because it operates at the kernel level where the attacker can access memory that should normally be protected from user-space access, making it a significant threat to system integrity and confidentiality.
The recommended mitigation for CVE-2023-0459 involves upgrading the Linux kernel beyond the specific commit 74e19ef0ff8061ef55957c3abd71614ef0f42f47 which contains the fix for this issue. This upgrade addresses the fundamental implementation flaw in the copy_from_user function's memory access validation. Organizations should prioritize applying this kernel update as soon as possible to protect against potential exploitation of this vulnerability. The fix implements proper uaccess_begin_nospec instrumentation that ensures the kernel's access_ok checks are properly enforced even under speculative execution conditions. This vulnerability aligns with CWE-122 (Heap-based Buffer Overflow) and represents a specific implementation weakness in kernel memory protection mechanisms that could be leveraged by adversaries following ATT&CK techniques related to privilege escalation and information gathering through kernel-level attacks.