CVE-2025-20748 is an out-of-bounds write vulnerability classified under CWE-787 found in the WLAN AP driver of several MediaTek chipsets, including MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The root cause is an incorrect bounds check in the driver code, which allows writing outside the intended memory buffer. This memory corruption can lead to local escalation of privilege if an attacker already has System-level privileges on the device. The vulnerability does not require user interaction for exploitation, but it does require the attacker to have high privileges initially, limiting remote exploitation potential. Affected versions include SDK release 7.6.7.2 and earlier, as well as openWRT versions 19.07 and 21.02, which are commonly used in embedded and networking devices. The CVSS v3.1 base score is 6.7, reflecting medium severity with high impact on confidentiality, integrity, and availability. No public exploits have been reported yet, but the vulnerability poses a significant risk in environments where local high-privilege access is possible. The issue is tracked internally by MediaTek under patch ID WCNCR00432679 and issue ID MSV-3950, though no public patch links are currently available.

This vulnerability allows an attacker with existing System privileges on affected devices to perform out-of-bounds writes, potentially leading to privilege escalation beyond the current level. This can compromise the confidentiality, integrity, and availability of the device and its data. In wireless access points and embedded systems using these MediaTek chipsets, successful exploitation could enable attackers to execute arbitrary code with elevated privileges, disrupt network services, or manipulate sensitive information. Organizations relying on these chipsets in critical infrastructure, enterprise networks, or IoT deployments face increased risk of internal attacks or lateral movement by malicious insiders or compromised administrators. The lack of required user interaction facilitates automated exploitation once local access is obtained. Although remote exploitation is unlikely without prior system access, the vulnerability significantly raises the stakes for devices already compromised or accessed by unauthorized personnel.

Organizations should monitor MediaTek advisories and apply official patches or firmware updates as soon as they become available to address this vulnerability. Until patches are released, restrict local administrative access to trusted personnel only and implement strict access controls and monitoring on devices using affected chipsets. Employ network segmentation to limit exposure of vulnerable devices to untrusted networks or users. Regularly audit device configurations and logs for suspicious activity indicative of privilege escalation attempts. For openWRT users, consider upgrading to versions beyond 21.02 once patched or applying vendor-provided backported fixes. Additionally, implement host-based intrusion detection systems (HIDS) to detect anomalous behavior resulting from exploitation attempts. Avoid running unnecessary services with elevated privileges on affected devices to reduce attack surface. Finally, maintain an inventory of devices using these MediaTek chipsets to prioritize remediation efforts effectively.