CVE-2025-20739 is a stack overflow vulnerability classified under CWE-121 found in the WLAN Access Point (AP) driver of several MediaTek chipsets, including MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The vulnerability stems from an incorrect bounds check in the driver code, which allows an out-of-bounds write operation on the stack. This flaw can be exploited by a local attacker who already possesses System-level privileges to escalate their privileges further, potentially gaining higher-level control over the affected device. The vulnerability does not require user interaction to be exploited, but it does require the attacker to have high privileges initially, which limits the attack surface to insiders or attackers who have already compromised the system to some extent. The affected software versions include MediaTek 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 base score is 6.7, indicating a medium severity with high impact on confidentiality, integrity, and availability, but limited by the requirement of local high privileges. No public exploits or active exploitation campaigns have been reported to date. The issue was publicly disclosed on November 4, 2025, and patches have been identified by MediaTek under patch ID WCNCR00435340 and issue ID MSV-4038, though direct patch links are not provided in the source data.

For European organizations, this vulnerability poses a risk primarily in environments where MediaTek chipsets are deployed in wireless infrastructure, including enterprise access points, routers, and embedded devices running affected SDK or OpenWRT versions. Successful exploitation could allow an attacker with existing System privileges to escalate their access, potentially leading to full device compromise. This could result in unauthorized access to sensitive network traffic, manipulation of device configurations, or disruption of wireless services, impacting confidentiality, integrity, and availability of critical network resources. Given the widespread use of MediaTek chipsets in consumer and enterprise wireless equipment, organizations in sectors such as telecommunications, manufacturing, and critical infrastructure could face increased risk. The lack of required user interaction facilitates stealthy exploitation once initial access is gained. However, the prerequisite of high privileges limits remote exploitation, making insider threats or post-compromise lateral movement more relevant. Failure to patch could enable attackers to solidify persistence and expand control within networks, complicating incident response and remediation efforts.

European organizations should immediately identify all devices using the affected MediaTek chipsets and verify the firmware or SDK versions in use, focusing on those running SDK release 7.6.7.2 or earlier and OpenWRT 19.07 or 21.02. Applying the official patches from MediaTek (patch ID WCNCR00435340) as soon as they become available is critical. Where patching is not immediately feasible, organizations should implement strict access controls to limit local administrative access to trusted personnel only, reducing the risk of privilege escalation. Network segmentation should be enforced to isolate wireless infrastructure devices from general user networks and sensitive systems. Monitoring for unusual local privilege escalation attempts and anomalous behavior on devices with affected chipsets can aid early detection. Additionally, organizations should review and harden device configurations, disable unnecessary services, and ensure firmware integrity checks are in place. For devices running OpenWRT, upgrading to versions beyond 21.02 that include the fix or applying vendor-provided patches is recommended. Regular vulnerability scanning and asset inventory updates will help maintain awareness of exposure. Finally, educating IT staff about the nature of this vulnerability and the importance of limiting high privilege access can reduce insider threat risks.