CVE-2025-20739 is a stack overflow vulnerability classified under CWE-121 found in the WLAN AP driver of several MediaTek chipsets including MT6890, MT7615, MT7622, MT7663, MT7915, MT7916, MT7981, and MT7986. The vulnerability stems from an incorrect bounds check in the driver code that leads to an out-of-bounds write on the stack. This memory corruption flaw can be exploited by an attacker who already has System-level privileges on the device to escalate their privileges further, potentially gaining higher control or bypassing security mechanisms. The flaw does not require user interaction, which means exploitation can be automated or triggered remotely if the attacker has system access. 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, the vulnerability poses a risk to the integrity and security of affected devices. The issue was reserved in November 2024 and published in November 2025, but no CVSS score has been assigned yet. The vulnerability is significant because stack overflows can lead to arbitrary code execution or system compromise if exploited successfully. The vulnerability's impact is limited by the prerequisite that the attacker must already have System privileges, which reduces the attack surface but still represents a critical escalation vector within compromised environments. MediaTek has identified the issue under internal tracking MSV-4038 and patch ID WCNCR00435340, though no public patch links are currently available. Organizations using affected MediaTek chipsets in wireless access points or embedded devices should prioritize patching once updates are released and monitor for any exploitation attempts.

For European organizations, this vulnerability could lead to local privilege escalation on devices using affected MediaTek chipsets, particularly wireless access points and embedded network devices. If an attacker gains System-level access—potentially through other vulnerabilities or insider threats—they could exploit this flaw to gain higher privileges, enabling them to manipulate device firmware, intercept or redirect network traffic, or disable security controls. This could compromise network integrity, confidentiality, and availability, especially in critical infrastructure or enterprise environments relying on these devices for secure wireless connectivity. The lack of user interaction requirement increases the risk of automated exploitation in compromised environments. The impact is heightened in scenarios where these devices serve as network gateways or are part of sensitive operational technology systems. Additionally, since openWRT is widely used in custom router deployments, organizations employing these versions are at risk. The vulnerability could facilitate lateral movement within networks, making incident containment more difficult. However, the prerequisite of existing System privileges limits the initial attack vector, meaning the vulnerability is more likely to be exploited as part of a multi-stage attack rather than as an initial entry point.

1. Monitor MediaTek and openWRT official channels closely for the release of patches addressing CVE-2025-20739 and apply them promptly to all affected devices. 2. Restrict administrative and system-level access to devices using these MediaTek chipsets to trusted personnel only, employing strong authentication and access controls. 3. Implement network segmentation to isolate devices with these chipsets, limiting the potential for lateral movement if a device is compromised. 4. Regularly audit and monitor device logs for unusual privilege escalation attempts or anomalous behavior indicative of exploitation attempts. 5. Where possible, replace or upgrade devices running vulnerable SDK or openWRT versions with newer, patched firmware or hardware. 6. Employ endpoint detection and response (EDR) solutions capable of detecting exploitation behaviors related to stack overflows and privilege escalation. 7. Conduct internal penetration testing and vulnerability assessments focusing on wireless infrastructure to identify and remediate privilege escalation vectors. 8. Educate system administrators about the risks of privilege escalation vulnerabilities and enforce the principle of least privilege to minimize the impact of potential exploits.