CVE-2025-20731 is a heap overflow vulnerability categorized under CWE-122 found in the WLAN 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 that leads to an out-of-bounds write operation on the heap. This flaw can be exploited locally by an attacker who already has System-level privileges, particularly when the OceReducedNeighborReport feature is disabled, to escalate privileges further. The vulnerability does not require user interaction, making it easier to exploit once local access is obtained. 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. Although no public exploits have been reported, the vulnerability poses a risk of privilege escalation, potentially allowing attackers to gain higher control over the device, which could lead to further compromise of network infrastructure. The CVSS v3.1 score of 5.3 reflects a medium severity, considering the attack vector is local, requires low complexity, and privileges are needed. The impact on confidentiality, integrity, and availability is limited but non-negligible due to the potential for privilege escalation. No patch links were provided, but MediaTek has assigned a patch ID (WCNCR00441511) and issue ID (MSV-4140), indicating that a fix is available or forthcoming.

For European organizations, this vulnerability could lead to local privilege escalation on devices using affected MediaTek chipsets, such as wireless access points, routers, or embedded IoT devices. This could allow attackers with initial system-level access to gain higher privileges, potentially enabling them to modify device configurations, intercept or manipulate network traffic, or deploy persistent malware. In critical infrastructure or enterprise environments, such privilege escalation could facilitate lateral movement within networks, increasing the risk of broader compromise. The impact is particularly significant for organizations relying on openWRT-based devices or custom firmware incorporating the vulnerable SDK versions. Disruption or compromise of wireless infrastructure could affect availability and confidentiality of communications. Although exploitation requires local access, insider threats or attackers who have already breached perimeter defenses could leverage this vulnerability to deepen their foothold. The absence of user interaction in exploitation further lowers barriers for attackers once local access is obtained.

European organizations should immediately identify devices using the affected MediaTek chipsets and verify the firmware versions against the vulnerable SDK releases and openWRT versions. Applying vendor-provided patches or firmware updates that address CVE-2025-20731 is critical. If patches are not yet available, consider disabling the OceReducedNeighborReport feature as a temporary mitigation to reduce exploitability. Network segmentation and strict access controls should be enforced to limit local access to wireless infrastructure devices, minimizing the risk of local exploitation. Regularly audit device configurations and monitor for unusual privilege escalations or anomalous activity on wireless access points. Employ endpoint protection and intrusion detection systems capable of detecting exploitation attempts targeting heap overflow vulnerabilities. For organizations using openWRT-based devices, ensure firmware is updated to versions beyond 21.02 or apply community patches addressing this issue. Finally, maintain an inventory of embedded devices and their firmware versions to streamline vulnerability management and patch deployment.