CVE-2026-20407 is a critical vulnerability identified in the WLAN STA driver of several MediaTek MT79xx series wireless chipsets, specifically MT7902, MT7920, MT7921, MT7922, MT7925, and MT7927. The root cause is a missing bounds check in the driver code, classified under CWE-787 (Out-of-bounds Write). This flaw allows an attacker with local user privileges to perform an out-of-bounds write operation, which can corrupt memory and escalate privileges to higher levels, potentially root or SYSTEM. The vulnerability does not require user interaction, making it easier to exploit once local access is obtained. The affected software versions include NB SDK release 3.8 and earlier. The CVSS v3.1 base score is 9.3, reflecting critical severity with high impact on confidentiality, integrity, and availability. The vector indicates local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), scope changed (S:C), and high impact on all security properties (C:H/I:H/A:H). Although no active exploits have been reported, the vulnerability's nature and severity necessitate prompt attention. The issue is tracked internally by MediaTek as MSV-4905 and patched under WCNCR00464377. The vulnerability affects wireless communication modules widely used in consumer devices, IoT, and enterprise networking hardware, potentially allowing attackers to gain unauthorized control over affected systems.

The vulnerability allows local attackers to escalate privileges from user-level to higher privileged levels, potentially root or SYSTEM, enabling full control over the affected device. This can lead to unauthorized access to sensitive data, modification or deletion of critical system files, installation of persistent malware, and disruption of wireless communications. Given the widespread deployment of MediaTek MT79xx chipsets in consumer electronics, IoT devices, and enterprise networking equipment, exploitation could compromise a large number of devices globally. The out-of-bounds write may also cause system instability or crashes, impacting availability. Organizations relying on these chipsets in critical infrastructure or sensitive environments face increased risk of data breaches, operational disruption, and lateral movement by attackers. The lack of need for user interaction lowers the barrier for exploitation once local access is obtained, increasing the threat level. Although no known exploits are currently active, the vulnerability's critical severity and broad impact necessitate urgent mitigation to prevent potential exploitation.

1. Apply the official MediaTek patch WCNCR00464377 as soon as it becomes available to address the out-of-bounds write vulnerability. 2. Upgrade affected devices to NB SDK versions later than 3.8 where the vulnerability is fixed. 3. Restrict local user access on devices using affected MediaTek chipsets to trusted personnel only, minimizing the risk of local exploitation. 4. Implement strict access controls and monitoring on endpoints with these wireless modules to detect suspicious local activity. 5. Employ endpoint detection and response (EDR) solutions capable of identifying anomalous behavior indicative of privilege escalation attempts. 6. For enterprise environments, consider network segmentation to isolate devices with vulnerable chipsets from critical systems. 7. Maintain up-to-date inventories of hardware using MediaTek MT79xx series chipsets to prioritize patch deployment. 8. Educate users about the risks of executing untrusted code locally, as local execution privileges are required for exploitation. 9. Monitor security advisories from MediaTek and related vendors for updates or additional mitigations. 10. If patching is delayed, consider temporary disabling or limiting WLAN functionality on affected devices where feasible to reduce attack surface.