CVE-2026-19676 in Zephyr
Summary
by MITRE • 10/22/2026
The user-mode verifier for the peci_transfer() system call, z_vrfy_peci_transfer() in drivers/peci/peci_handlers.c, checked only the device object permission and copied the caller-supplied struct peci_msg with k_usermode_from_copy(). That copy validates the outer structure only; the buf pointers and len values inside the embedded struct peci_buf members tx_buffer and rx_buffer remained fully caller-controlled and were passed unchecked to the driver.
Every in-tree PECI driver dereferences those pointers in supervisor mode: peci_npcx_transfer() in drivers/peci/peci_npcx.c and peci_it8xxx2_transfer() in drivers/peci/peci_ite_it8xxx2.c copy hardware bytes into rx_buffer.buf[i] and read command bytes out of tx_buffer.buf[i], and peci_xec_read()/peci_xec_write() in drivers/peci/peci_mchp_xec.c do the same with no bound on rx_buffer.len at all. A user-mode thread that has been granted the PECI device object — the normal way an application exposes a device under CONFIG_USERSPACE — could therefore point rx_buffer.buf at kernel data structures and have the driver write hardware-supplied bytes there, or point tx_buffer.buf at kernel memory and have its contents pushed onto the PECI/eSPI out-of-band bus.
The impact is a full user-mode-to-kernel escape: an arbitrary kernel write primitive (integrity and, through it, code execution at supervisor privilege), an arbitrary kernel read disclosed to a PECI bus observer, and a trivially reachable supervisor-mode fault if an unmapped address is supplied. Exploitation requires CONFIG_USERSPACE=y, one of the PECI drivers enabled (CONFIG_PECI_NPCX, CONFIG_PECI_XEC or CONFIG_PECI_ITE_IT8XXX2), and local code execution in a user-mode thread holding the PECI device.
The fix adds K_SYSCALL_MEMORY_READ() and K_SYSCALL_MEMORY_WRITE() checks over the two embedded buffers, with a size_add_overflow() guard on the frame-check-sequence byte accounted for in the RX length.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified as CVE-2024-something involves a critical privilege escalation flaw within the Peripheral Component Interconnect Express (PECI) subsystem of the Zephyr real-time operating system, specifically affecting the user-mode verifier function z_vrfy_peci_transfer located in drivers/peci/peci_handlers.c. This security defect stems from an incomplete validation mechanism during the handling of PECI transfer requests initiated by unprivileged applications. Under normal operation with CONFIG_USERSPACE enabled, applications interact with hardware devices through a controlled interface that is supposed to enforce strict boundaries between user space and kernel space memory regions. However, in this specific implementation, while the verifier correctly checks permissions for the primary device object and performs an initial copy of the outer struct peci_msg structure using k_usermode_from_copy(), it fails to validate the internal pointers contained within nested structures. Specifically, the buf pointers and length values associated with the tx_buffer and rx_buffer members of embedded struct peci_buf objects remain entirely under caller control without any subsequent integrity checks or boundary validations before being passed directly to the underlying driver implementations.
This architectural oversight allows a malicious user-mode thread that has been granted access to the PECI device object to manipulate memory addresses in ways that bypass standard security controls. The vulnerability is particularly severe because every active in-tree PECI driver, including peci_npcx_transfer for NXP controllers, peci_it8xxx2_transfer for ITE controllers, and peci_xec_read/peci_xec_write for Microchip XEC devices, operates these pointers in supervisor mode without verifying their validity or bounds. These drivers directly dereference the provided buffers to read command bytes from tx_buffer.buf[i] and write hardware-returned data into rx_buffer.buf[i]. In several implementations, such as those for the PECI_XEC driver, there is no bound on the rx_buffer.len value at all, meaning a user can specify an arbitrarily large length. Consequently, if a user-mode application points the rx_buffer.buf to kernel memory addresses, the hardware will write incoming data directly into protected kernel structures via DMA or direct bus access mechanisms. Conversely, pointing tx_buffer.buf to kernel memory allows sensitive internal state information to be read out and transmitted over the PECI or eSPI out-of-band management bus, potentially exposing cryptographic keys, system configuration details, or other privileged data to external observers connected to these low-level hardware interfaces.
The operational impact of this vulnerability constitutes a full user-mode-to-kernel escape vector with significant consequences for system integrity and confidentiality. An attacker can achieve an arbitrary kernel write primitive by supplying crafted buffer pointers that target specific kernel memory locations where they wish to inject malicious code or alter critical data structures, thereby gaining the potential for arbitrary code execution at supervisor privilege levels. Additionally, the vulnerability provides a trivially reachable mechanism for arbitrary kernel reads; any content from kernel space can be exfiltrated through the PECI bus if an observer is present on that physical interface. Furthermore, supplying unmapped addresses results in immediate supervisor-mode faults, which could lead to denial of service conditions or further exploitation attempts depending on how the system handles such exceptions. The exploitability requires specific configuration states: CONFIG_USERSPACE must be enabled, one of the affected PECI drivers (CONFIG_PECI_NPCX, CONFIG_PECI_XEC, or CONFIG_PECI_ITE_IT8XXX2) must be compiled into the kernel, and the attacker must have local code execution capabilities within a user-mode thread that holds the necessary permissions for the PECI device object.
From a classification perspective, this vulnerability aligns with CWE-94 Improper Control of Generation of Code (Code Injection) due to the potential for arbitrary code execution via memory corruption, as well as CWE-200 Exposure of Sensitive Information to an Unauthorized Actor regarding the kernel read capability. In terms of the MITRE ATT&CK framework, this represents a technique consistent with T1059 Command and Scripting Interpreter if viewed through the lens of initial access leading to privilege escalation, but more accurately maps to T1068 Exploitation for Privilege Escalation by leveraging improper input validation in system calls. The root cause is fundamentally an insecure direct object reference combined with insufficient boundary checks on memory pointers passed from user space to kernel space during hardware interaction routines.
The remediation strategy implemented addresses these flaws by introducing rigorous memory access verification mechanisms before the buffers are utilized by the drivers. Specifically, the fix incorporates K_SYSCALL_MEMORY_READ and K_SYSCALL_MEMORY_WRITE macros to validate that the target memory regions for both transmission and reception buffers reside within valid user-space address ranges accessible to the calling process. This ensures that pointers cannot be directed toward kernel space or other protected memory segments. Additionally, a size_add_overflow guard has been added to account for the frame-check-sequence byte in the RX length calculation, preventing integer overflow issues that could lead to buffer overruns even if valid user-space addresses were provided. These changes enforce strict adherence to memory isolation principles mandated by modern operating system security models, ensuring that hardware interactions remain confined within the boundaries of authorized user-mode allocations and do not compromise kernel integrity or confidentiality.