CVE-2026-99232 in Linux
Summary
by MITRE • 11/02/2026
In the Linux kernel, the following vulnerability has been resolved:
tracing/syscalls: Use copy_from_user for the faultable syscall buffer
syscall_copy_user_array() copies the buffer argument of faultable syscalls (write, pwrite64, ...) with __copy_from_user(), which skips access_ok(). Use copy_from_user() instead so a non-user address is rejected and the entry is recorded as faulted.
It could be a security concern for machines that trust perf a bit too much.
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Analysis
by VulDB Data Team • 11/02/2026
The Linux kernel tracing subsystem contains a specific implementation flaw within the handling of syscall arguments for tracepoints, specifically affecting functions designed to copy data from user space into kernel buffers during the recording of system call events. The vulnerability centers on the use of __copy_from_user() in the syscall_copy_user_array function when processing faultable syscalls such as write and pwrite64. While __copy_from_user is generally intended for performance optimization by bypassing certain safety checks under controlled conditions, its application here without a preceding access verification creates a significant security gap. The core issue lies in the omission of the access_ok() check, which serves as the primary gatekeeper to ensure that memory addresses provided by user-space applications are valid and accessible within the permitted address space boundaries. By skipping this validation step before attempting to copy data, the kernel fails to reject non-user addresses or invalid pointers, thereby allowing potentially malicious or malformed inputs to bypass standard security checks during tracepoint recording.
This technical flaw has direct implications for system integrity and stability, particularly in environments where performance monitoring tools like perf are granted elevated privileges or deep access to kernel internals. When a user-space process provides an address that does not belong to its own memory space or is otherwise invalid, the kernel proceeds with the copy operation without verifying legitimacy. This can lead to several adverse outcomes including data corruption if the target buffer overlaps with critical kernel structures, potential information disclosure by reading unintended memory regions, or system crashes due to page faults occurring in contexts where they are not properly handled. The risk is exacerbated because tracing mechanisms often run with high privileges and deep visibility into process states, making them attractive targets for exploitation by attackers seeking to escalate privileges or disrupt service availability through denial-of-service attacks triggered via malformed syscall arguments.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation as the root cause stems from failing to adequately validate user-supplied input before processing it within privileged kernel code. Additionally, it relates to CWE-787 Out-of-bounds Write if the invalid address leads to writing beyond allocated buffers, and potentially CWE-416 Use After Free if the operation interacts with memory that has been deallocated or is otherwise inaccessible. In terms of adversary behavior mapping under MITRE ATT&CK, this flaw could be leveraged in techniques associated with Defense Evasion by manipulating tracepoint data to hide malicious activity, or Privilege Escalation if an attacker can exploit the improper validation to execute arbitrary code within kernel space. The trust placed in performance monitoring tools often leads administrators to overlook potential attack vectors originating from these subsystems, making this oversight particularly dangerous for systems relying heavily on perf for diagnostics and security auditing.
To mitigate this vulnerability, it is imperative that developers replace __copy_from_user() with copy_from_user() in the relevant syscall tracing functions. The standard copy_from_user function includes necessary checks such as access_ok(), ensuring that only valid user-space addresses are processed during data transfer operations. This change enforces proper boundary checking and prevents the kernel from accepting memory references that fall outside of permitted ranges, thereby closing the gap that allows non-user addresses to be misinterpreted as legitimate inputs. System administrators should ensure their kernels are updated with patches addressing this specific issue in the tracing subsystem. Furthermore, organizations employing performance monitoring tools should review their configurations to limit access to tracepoints where possible and monitor for unusual patterns in syscall arguments that might indicate exploitation attempts targeting these validation weaknesses. Regular auditing of kernel code changes related to user-space interaction points remains essential to maintaining robust security postures against input-based vulnerabilities.