CVE-2025-20735 is a heap overflow vulnerability classified under CWE-122, found in the WLAN Access Point (AP) driver of multiple MediaTek chipsets including MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The root cause is an incorrect bounds check in the driver code, which leads to an out-of-bounds write on the heap. This memory corruption can be exploited by a local attacker with user-level execution privileges to escalate their privileges to a higher level, potentially root or system-level access. Exploitation does not require user interaction, increasing the risk of automated or stealthy attacks. The 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. Although no public exploits have been reported yet, the vulnerability's nature suggests that once weaponized, it could allow attackers to compromise device integrity, bypass security controls, and potentially pivot within networks. The vulnerability was reserved in November 2024 and published in November 2025, with no CVSS score assigned at the time of reporting. The absence of a patch link indicates that remediation may still be pending or in progress. This vulnerability is significant because MediaTek chipsets are widely deployed in consumer and enterprise wireless equipment, making the attack surface broad. The flaw's exploitation could undermine confidentiality, integrity, and availability of affected devices, especially in environments where local user access is possible. The vulnerability's local scope and requirement for user privileges limit remote exploitation but do not eliminate risk in multi-user or shared environments.

For European organizations, this vulnerability poses a considerable risk to the security of wireless networking infrastructure that relies on affected MediaTek chipsets. The ability to escalate privileges locally can allow attackers to gain administrative control over routers, access points, or IoT devices, potentially leading to network compromise, interception of sensitive communications, or deployment of persistent malware. Sectors such as telecommunications, critical infrastructure, manufacturing, and enterprise IT environments that deploy embedded wireless devices are particularly vulnerable. The impact extends to operational disruptions, data breaches, and erosion of trust in network security. Given the widespread use of openWRT in European networking devices, organizations using these platforms are at heightened risk. The lack of user interaction for exploitation means that insider threats or compromised user accounts could quickly escalate privileges without alerting users. Additionally, the vulnerability could be leveraged in targeted attacks against high-value assets or supply chain components. The potential for lateral movement within networks following privilege escalation increases the threat to broader organizational security.

Organizations should prioritize identifying devices running the affected MediaTek chipsets and firmware versions, including openWRT 19.07 and 21.02 or SDK releases 7.6.7.2 and earlier. Immediate mitigation involves restricting local user access to these devices, enforcing strict access controls, and monitoring for unusual privilege escalation attempts. Network segmentation can reduce the risk of lateral movement if a device is compromised. Administrators should subscribe to MediaTek security advisories and apply patches or firmware updates as soon as they become available. Where patches are delayed, consider deploying host-based intrusion detection systems (HIDS) or endpoint protection solutions capable of detecting anomalous behavior indicative of heap overflow exploitation. Regularly audit device configurations and user permissions to minimize unnecessary local privileges. For openWRT users, upgrading to newer, patched releases or applying vendor-provided patches is critical. Additionally, implement robust logging and alerting mechanisms to detect exploitation attempts early. In environments where physical or local access cannot be fully controlled, consider device replacement or isolation until remediation is possible.