CVE-2025-20729 is a heap overflow vulnerability classified under CWE-122 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, 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, enabling them to escalate privileges further or compromise system integrity. Notably, exploitation does not require user interaction, increasing the risk in environments where attackers have some level of system access. The affected software includes SDK release 7.6.7.2 and earlier, and openWRT versions 19.07 and 21.02, which are commonly used in embedded devices and routers. Although no public exploits have been reported, the vulnerability's presence in widely deployed MediaTek chipsets used in access points and routers makes it a significant concern. The vulnerability was reserved in November 2024 and published in November 2025, but no CVSS score has been assigned yet. The lack of a patch link suggests that organizations should monitor vendor communications closely for updates. The vulnerability's impact is primarily on the integrity and confidentiality of affected systems, as it allows privilege escalation from an already privileged context. This could lead to unauthorized modifications, persistent malware installation, or disruption of network services.

For European organizations, the impact of CVE-2025-20729 can be substantial, especially for those relying on MediaTek-based wireless access points and routers in their network infrastructure. Privilege escalation vulnerabilities in network devices can lead to full device compromise, allowing attackers to manipulate network traffic, intercept sensitive data, or disrupt connectivity. Critical sectors such as telecommunications, government, finance, and healthcare that deploy these devices at scale could face increased risk of targeted attacks or insider threats exploiting this flaw. The vulnerability's requirement for existing System privileges limits remote exploitation but does not eliminate risk, as attackers who gain initial footholds through other means could leverage this flaw to deepen their access. Additionally, the absence of user interaction for exploitation facilitates automated or stealthy attacks. The use of openWRT in many European ISP-provided routers and embedded devices further broadens the attack surface. Unpatched devices could become entry points for lateral movement within corporate or critical infrastructure networks, potentially leading to data breaches or service outages.

Organizations should immediately identify and inventory devices using the affected MediaTek chipsets and software versions, including those running openWRT 19.07 and 21.02. Applying vendor-provided patches or firmware updates as soon as they become available is critical. Until patches are deployed, network segmentation should be enforced to isolate vulnerable devices from sensitive systems and limit administrative access to trusted personnel only. Employ strict access controls and monitor for unusual privilege escalation attempts or anomalous behavior on devices with these chipsets. Consider disabling unnecessary services or features in the WLAN AP driver to reduce the attack surface. For openWRT users, upgrading to newer, patched versions or applying community patches is advisable. Regularly audit device configurations and firmware integrity to detect unauthorized changes. Additionally, implement endpoint detection and response (EDR) solutions to identify potential exploitation attempts. Collaborate with vendors and security communities to stay informed about emerging exploits and mitigation strategies.