CVE-2025-20738 is a stack overflow vulnerability classified under CWE-121, found in the WLAN Access Point (AP) driver software of MediaTek chipsets MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The root cause is an incorrect bounds check in the driver code that leads to an out-of-bounds write on the stack. This memory corruption can be exploited by a local attacker who already possesses System-level privileges to escalate their privileges further, potentially gaining higher control over the device or system. The vulnerability does not require user interaction, which simplifies exploitation once the attacker has initial access. Affected software 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 wireless devices and routers. The CVSS v3.1 score of 6.7 reflects a medium severity rating, with the vector indicating local attack vector (AV:L), low attack complexity (AC:L), high privileges required (PR:H), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). No public exploit code or active exploitation has been reported to date. The vulnerability is significant for embedded systems and IoT devices that rely on these MediaTek chipsets for wireless connectivity, as exploitation could lead to full system compromise or disruption of network services. Vendors and users should monitor for patches and updates to mitigate this risk.

For European organizations, this vulnerability poses a risk primarily in environments where MediaTek chipsets are deployed in wireless access points, routers, or embedded IoT devices. Successful exploitation could allow an attacker with existing System privileges to escalate their access, potentially leading to full device compromise, unauthorized data access, or disruption of network services. This could affect confidentiality, integrity, and availability of critical network infrastructure. Industries such as telecommunications, manufacturing, healthcare, and smart city infrastructure that deploy embedded wireless devices are particularly at risk. Given the medium severity and the requirement for prior System-level access, the threat is more relevant in scenarios where attackers have already breached perimeter defenses or insider threats exist. The lack of user interaction requirement increases the risk of automated or stealthy exploitation once initial access is gained. The vulnerability could also facilitate lateral movement within networks, increasing the potential impact on enterprise environments.

Organizations should inventory their network devices and embedded systems to identify those using affected MediaTek chipsets and software versions (SDK release 7.6.7.2 and earlier, openWRT 19.07 and 21.02). Immediate mitigation includes applying vendor patches or firmware updates once released. Until patches are available, restricting local administrative access to trusted personnel and implementing strict access controls can reduce the risk of exploitation. Network segmentation should be employed to limit lateral movement from compromised devices. Monitoring for unusual privilege escalation attempts or anomalous behavior on devices with these chipsets is recommended. Additionally, organizations should consider deploying host-based intrusion detection systems (HIDS) capable of detecting stack overflow exploitation attempts. For openWRT users, upgrading to newer, patched versions is critical. Vendors should be engaged to confirm patch availability and timelines. Finally, implementing robust endpoint security and maintaining least privilege principles will help mitigate the impact of any successful exploitation.