CVE-2025-20736 is a stack overflow vulnerability classified under CWE-121 found in the WLAN Access Point (AP) driver of several MediaTek chipsets (MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, MT7986). The root cause is an incorrect bounds check in the driver code, which allows an out-of-bounds write to occur. This memory corruption can be leveraged by a local attacker who already possesses System-level privileges to escalate their privileges further, potentially gaining higher-level control or bypassing security mechanisms. The vulnerability does not require user interaction, increasing the risk of automated or stealthy exploitation. It affects SDK releases up to 7.6.7.2 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 6.7, reflecting a medium severity with high impact on confidentiality, integrity, and availability, but requiring high privileges for exploitation. No public exploits have been reported yet, but the presence of the vulnerability in widely deployed wireless chipsets makes it a significant concern for network security. The issue was assigned by MediaTek and published in November 2025, with a patch identifier WCNCR00435347 and issue ID MSV-4049, though no direct patch links were provided in the source data.

For European organizations, this vulnerability poses a risk primarily to the security and stability of wireless network infrastructure that uses affected MediaTek chipsets. Successful exploitation could allow attackers with existing System privileges to escalate their access, potentially leading to full device compromise, unauthorized data access, or disruption of network services. This could impact confidentiality by exposing sensitive network traffic or credentials, integrity by allowing unauthorized configuration changes or firmware manipulation, and availability by causing device crashes or denial of service. Given the widespread use of MediaTek chipsets in consumer and enterprise-grade wireless routers and access points, organizations relying on these devices for critical communications or IoT connectivity could face increased risk. The lack of required user interaction facilitates stealthy attacks, and the medium severity score indicates a significant but not critical threat level. The vulnerability could also be leveraged as part of a multi-stage attack chain, especially in environments where attackers have already gained some level of system access.

Organizations should promptly identify devices using the affected MediaTek chipsets and verify the firmware or SDK versions in use, particularly checking for SDK releases up to 7.6.7.2 and openWRT versions 19.07 and 21.02. Applying vendor-provided patches or firmware updates that address this vulnerability is the most effective mitigation. In the absence of immediate patches, network segmentation should be employed to limit access to vulnerable devices, restricting administrative access to trusted personnel and systems. Monitoring for unusual local privilege escalation attempts on devices with these chipsets is recommended, including enhanced logging and alerting for suspicious driver or kernel activity. Additionally, organizations should enforce the principle of least privilege to minimize the number of users or processes with System-level access, reducing the attack surface. Regularly updating and auditing wireless infrastructure and embedded device firmware can prevent exploitation of similar vulnerabilities. Finally, consider isolating or replacing legacy devices that cannot be updated with secure alternatives.