CVE-2026-68435 in Linux
Summary
by MITRE • 08/12/2026
In the Linux kernel, the following vulnerability has been resolved:
LoongArch: Fix address space mismatch in kexec command line lookup
When searching the loaded segments for the "kexec" command line marker, the kexec_load(2) path (file_mode == 0) passes the user-space segment buffer straight to strncmp() through a bogus (char __user *) cast. This dereferences a user pointer in kernel context, which is wrong and is flagged by sparse:
arch/loongarch/kernel/machine_kexec.c:84:51: sparse: incorrect type in argument 2 (different address spaces) @@ expected char const * @@ got char [noderef] __user *
Here copy the marker-sized prefix of each segment into a small on-stack buffer with copy_from_user() before comparing, and skip segments that fault. The subsequent copy_from_user() that stages the full command line into the safe area is left unchanged.
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Analysis
by VulDB Data Team • 08/12/2026
This vulnerability represents a critical kernel memory safety issue affecting the LoongArch architecture within the Linux kernel's kexec implementation. The flaw occurs during the kexec_load system call processing when the kernel attempts to locate command line markers within loaded memory segments. The vulnerability stems from improper handling of user-space memory pointers during kernel context operations, creating a dangerous address space mismatch that violates fundamental security principles of kernel operation.
The technical root cause involves a type casting error where the kernel code incorrectly passes a user-space pointer directly to the strncmp function through an invalid (char __user ) cast. This pattern creates a scenario where kernel code dereferences user memory addresses while operating in kernel context, bypassing essential memory protection mechanisms. The sparse static analysis tool correctly identifies this as a type mismatch between expected char const and the actual char [noderef] __user * pointer, highlighting the fundamental violation of address space separation principles that are core to kernel security architecture.
The operational impact of this vulnerability is severe as it enables potential privilege escalation attacks through kernel memory corruption. An attacker with access to execute kexec_load operations could manipulate the command line marker lookup process to cause unexpected behavior in kernel memory management or potentially gain unauthorized code execution privileges. This represents a classic case of improper kernel memory handling that violates the principle of least privilege and address space isolation that forms the foundation of modern operating system security models.
The fix implemented addresses this vulnerability by introducing proper memory validation procedures that copy the marker-sized prefix from each user-space segment into a controlled on-stack buffer using the copy_from_user() function. This approach ensures that all user-space memory access occurs through proper kernel interfaces rather than direct pointer dereferencing. The solution also includes fault handling for segments that fail during the copy operation, making the implementation robust against malformed or inaccessible memory regions while maintaining the original functionality for legitimate command line processing.
This vulnerability aligns with CWE-476 which describes NULL pointer dereference issues and represents a specific instance of improper access to user-space memory from kernel context. The fix demonstrates proper adherence to security best practices by implementing defensive programming techniques that prevent unauthorized memory access patterns. From an ATT&CK perspective, this vulnerability could be categorized under privilege escalation techniques where the improper memory handling creates a path for attackers to manipulate kernel operations through carefully crafted input data. The remediation approach follows established kernel security guidelines that emphasize proper memory validation and the use of safe copy functions when transitioning between user and kernel address spaces, ensuring that the solution maintains system stability while preventing potential exploitation vectors.