CVE-2025-20735 is a heap overflow vulnerability classified under CWE-122, found in the WLAN Access Point (AP) driver of several MediaTek chipsets including 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 heap memory. This flaw can be exploited by an attacker with local user execution privileges to escalate their privileges to higher levels, potentially gaining kernel or administrative rights. Notably, exploitation does not require any user interaction, which increases the risk of automated or stealthy attacks. The affected products 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 devices and wireless routers. The vulnerability impacts confidentiality, integrity, and availability, as an attacker could execute arbitrary code, manipulate sensitive data, or cause denial of service. The CVSS v3.1 score of 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) indicates a high severity with local attack vector, low complexity, requiring low privileges but no user interaction. Although no known exploits are currently in the wild, the vulnerability's nature and affected widespread chipsets make it a critical concern for embedded device security. The issue was publicly disclosed on November 4, 2025, with a patch identified as WCNCR00435349, though no direct patch links are provided in the data.

For European organizations, this vulnerability poses a significant risk particularly to those deploying MediaTek-based wireless access points, routers, or embedded IoT devices running affected SDK or openWRT firmware versions. Successful exploitation could allow attackers with limited local access to escalate privileges, potentially gaining control over network infrastructure devices. This could lead to interception or manipulation of network traffic, disruption of wireless services, and compromise of connected systems. Critical sectors such as telecommunications, manufacturing, and public services that rely on embedded wireless devices could face operational disruptions and data breaches. The lack of required user interaction increases the likelihood of automated exploitation in internal networks. Given the widespread use of openWRT in European networking equipment and the popularity of MediaTek chipsets in consumer and industrial devices, the threat surface is substantial. Additionally, the vulnerability could be leveraged in targeted attacks against organizations with sensitive wireless infrastructure, amplifying the impact on confidentiality and availability.

Organizations should prioritize applying official patches from MediaTek or device vendors as soon as they become available, specifically targeting SDK releases up to 7.6.7.2 and openWRT versions 19.07 and 21.02. In the absence of immediate patches, network administrators should restrict local user access to affected devices by enforcing strict access controls and monitoring for unusual local activity. Deploying host-based intrusion detection systems (HIDS) on devices running vulnerable firmware can help detect exploitation attempts. Network segmentation should be implemented to isolate critical wireless infrastructure from general user networks, reducing the risk of privilege escalation spreading. Firmware integrity verification and regular audits of device configurations can prevent unauthorized modifications. Additionally, organizations should consider upgrading to newer firmware versions or alternative hardware platforms that do not contain this vulnerability. Security teams should also monitor threat intelligence feeds for emerging exploit code and indicators of compromise related to this CVE to enable rapid response.