CVE-2025-20735 is a heap overflow vulnerability classified under CWE-122 found in the WLAN Access Point (AP) driver of multiple MediaTek chipsets (MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, MT7986). The root cause is an incorrect bounds check in the driver code that allows an out-of-bounds write to heap memory. This flaw can be triggered by a local user with execution privileges on the device, without requiring any additional user interaction, making it a local privilege escalation vulnerability. The heap overflow can corrupt memory, potentially allowing an attacker to execute arbitrary code with elevated privileges, leading to full system compromise. The affected software versions include SDK release 7.6.7.2 and earlier, and openWRT versions 19.07 and 21.02, which are commonly used in embedded wireless devices and routers. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity but requiring local privileges. No public exploits have been reported yet, but the vulnerability poses a significant risk due to the widespread use of these chipsets in consumer and enterprise wireless infrastructure. MediaTek has assigned Patch ID WCNCR00435349 and Issue ID MSV-4051 to address this issue, though no direct patch links are currently provided.

The vulnerability enables a local attacker with user-level execution privileges to escalate to higher privileges by exploiting a heap overflow in the WLAN AP driver. This can lead to full compromise of the affected device, including unauthorized access to sensitive data, modification or deletion of critical system files, and disruption of network services. For organizations, this could mean compromised wireless infrastructure, allowing attackers to pivot into internal networks, intercept or manipulate network traffic, and disrupt business operations. The impact is especially severe in environments relying on MediaTek-based wireless access points or embedded devices running vulnerable SDKs or openWRT versions. The lack of required user interaction lowers the barrier for exploitation once local access is obtained, increasing the risk in multi-tenant or shared environments. Although no exploits are currently known in the wild, the vulnerability’s characteristics make it a prime target for attackers seeking persistent access or lateral movement within networks.

Organizations should promptly identify devices using the affected MediaTek chipsets and verify the firmware or SDK versions in use. Immediate mitigation involves upgrading to patched versions of the SDK or openWRT once MediaTek releases them. In the interim, restrict local user access to trusted personnel only and implement strict access controls to limit the ability of unprivileged users to execute code on affected devices. Network segmentation can reduce the risk of lateral movement if a device is compromised. Monitoring for anomalous behavior or privilege escalation attempts on wireless infrastructure devices is recommended. Additionally, consider disabling or limiting WLAN AP driver functionalities where feasible until patches are applied. Coordination with device vendors and firmware providers to obtain and deploy official patches is critical. Finally, maintain updated inventories of embedded devices and apply security best practices for embedded system hardening.