CVE-2025-20729 is a heap overflow vulnerability classified under CWE-122, found in the WLAN 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 allows an out-of-bounds write to heap memory. This flaw can be exploited locally by an attacker who already possesses System-level privileges on the device, enabling them to escalate privileges further or cause memory corruption. The vulnerability does not require user interaction, increasing the risk of automated or stealthy exploitation. Affected firmware 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 observed, the vulnerability's presence in widely deployed wireless chipsets makes it a significant concern. The CVSS v3.1 base score is 4.2, reflecting the requirement for high privileges to exploit and the limited scope of impact. The issue has been assigned Patch ID WCNCR00441512 and Issue ID MSV-4153 by MediaTek, but no public patches or exploit code are currently available.

The vulnerability allows a local attacker with System privileges to perform an out-of-bounds write on the heap, potentially leading to privilege escalation, arbitrary code execution, or system instability. This can compromise the confidentiality, integrity, and availability of the affected device. Since the affected chipsets are embedded in many wireless access points, routers, and IoT devices, exploitation could disrupt network infrastructure or enable attackers to gain deeper control over network devices. Organizations relying on these chipsets in critical environments such as enterprise networks, telecommunications, or industrial control systems may face increased risk of targeted attacks. The lack of required user interaction facilitates stealthy exploitation by insiders or malware already present on the device. Although exploitation requires existing high privileges, the vulnerability could be chained with other flaws to achieve full system compromise.

Organizations should monitor MediaTek and device vendor advisories for official patches addressing this vulnerability and apply them promptly. Until patches are available, restrict access to devices running affected chipsets to trusted administrators only, minimizing the risk of local exploitation. Employ strict access controls and endpoint protection to prevent unauthorized elevation to System privileges. Network segmentation can limit the impact of compromised devices. For openWRT users, consider upgrading to versions beyond 21.02 once patched releases are available. Conduct thorough audits of devices using these chipsets to identify and isolate vulnerable hardware. Implement runtime protections such as heap integrity checks or exploit mitigation technologies where supported. Finally, maintain robust logging and monitoring to detect anomalous behavior indicative of exploitation attempts.