CVE-2026-87765 in Unisoc
Summary
by MITRE • 10/12/2026
In the kernel apsys DVFS driver, there is a possible out-of-bounds read or hardware register corruption due to improper input validation of the frequency index. This could lead to system instability or denial of service with local privileges.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified within the Linux kernel's apsys Dynamic Voltage and Frequency Scaling (DVFS) driver represents a critical flaw in how the operating system manages hardware performance states for specific System-on-Chip architectures, particularly those found in MediaTek mobile devices. DVFS is a power management technique that dynamically adjusts the voltage and frequency of a processor core to balance performance with energy consumption. The apsys driver serves as an intermediary between the kernel's generic clock framework and the underlying hardware registers that control these adjustments. When a user-space application or a privileged process requests a change in CPU frequency, it typically passes an index value corresponding to a predefined operating point defined in the device tree or firmware tables. This vulnerability arises because the apsys driver fails to rigorously validate this input index against the bounds of the available performance state array before proceeding with hardware register writes.
From a technical perspective, the core issue is an improper input validation mechanism that allows for out-of-bounds access. In C-based kernel drivers, accessing memory or hardware registers outside their allocated boundaries can lead to undefined behavior. If the provided frequency index exceeds the maximum valid index defined by the driver's internal data structures, the code may read from invalid memory locations, potentially exposing sensitive kernel data through side-channel effects, although the primary risk described is more severe. More critically, an out-of-bounds write or misinterpreted register address can result in hardware register corruption. The DVFS mechanism relies on precise bit manipulation within specific control registers to set voltage levels and clock dividers. Writing incorrect values due to a miscalculated memory offset can corrupt these settings, causing the CPU core to operate at unsafe electrical parameters or enter an undefined state from which it cannot recover without a hard reset.
The operational impact of this vulnerability is significant for system stability and availability. An attacker with local privileges on the target device could exploit this flaw by crafting specific ioctl calls or sysfs writes that supply maliciously crafted frequency indices. Successful exploitation would likely result in immediate system instability, manifesting as kernel panics, freezes, or spontaneous reboots. This constitutes a Denial of Service (DoS) condition against the local user and potentially other users sharing the same physical device if the corruption affects shared hardware resources such as clock gates for peripherals like display controllers or network interfaces. While the requirement for local privileges limits the attack surface compared to remote exploits, it remains highly relevant in multi-user environments, containerized systems, or scenarios where a compromised application gains elevated access through other means.
This vulnerability aligns with CWE-125, which describes Out-of-Bounds Read, and potentially CWE-787 if the corruption leads to arbitrary write capabilities via register manipulation. In terms of offensive security frameworks, this falls under MITRE ATT&CK technique T1496, Resource Hijacking, specifically within the context of Denial of Service through resource exhaustion or system instability caused by improper input validation in kernel drivers. The lack of boundary checks is a classic software engineering error that persists even in mature codebases due to complex hardware abstraction layers and performance optimization pressures that sometimes bypass rigorous safety checks.
Mitigation strategies must focus on both immediate patching and long-term defensive coding practices. For system administrators, the primary mitigation is applying vendor-provided kernel updates or security patches that include bounds checking logic within the apsys driver's frequency selection functions. Developers should implement strict validation routines that compare the requested index against the maximum size of the supported operating points array before any hardware interaction occurs. If an invalid index is detected, the function should return an error code such as -EINVAL rather than proceeding with potentially destructive operations. Furthermore, adopting static analysis tools and fuzzing techniques during the development lifecycle can help identify similar input validation gaps in other kernel drivers. Enabling Kernel Hardening features like CONFIG_STRICT_DEVMEM and enforcing strict access controls on device nodes also reduces the risk of exploitation by limiting the attack surface available to local users.