CVE-2025-20751 is a medium-severity vulnerability classified as an out-of-bounds write (CWE-787) in the modem firmware of numerous MediaTek chipsets, specifically versions identified as Modem NR15. The vulnerability arises from a missing bounds check in the modem's processing logic, which can be triggered remotely when a user equipment (UE) device connects to a rogue base station controlled by an attacker. This out-of-bounds write can cause the modem system to crash, resulting in a denial of service condition. The attack vector requires network-level access to the cellular connection but does not require any user interaction or elevated privileges, making it a relatively straightforward attack if the attacker can establish a rogue base station. The affected chipsets span a wide range of MediaTek's modem products, including MT2735, MT6833 series, MT6853 series, MT6873 series, MT6880 series, MT6890 series, MT8675, MT8771, MT8791 series, and MT8797. The vulnerability was published on December 2, 2025, with a CVSS v3.1 score of 5.3, reflecting a network attack vector with high attack complexity and low privileges required, but only impacting availability. MediaTek has released a patch identified as MOLY01661195 to address this issue. No exploits have been reported in the wild to date. The vulnerability primarily threatens the availability of devices relying on these modems, potentially disrupting communications and services dependent on cellular connectivity.

For European organizations, this vulnerability poses a risk primarily to the availability of cellular-connected devices and infrastructure. Telecommunications providers using affected MediaTek modems in their network equipment or customer premises equipment (CPE) could experience service disruptions if attackers deploy rogue base stations to trigger modem crashes. Critical sectors such as emergency services, transportation, and industrial IoT deployments relying on cellular connectivity may face operational interruptions. Enterprises using mobile devices or embedded systems with these chipsets could see degraded service or device reboots, impacting business continuity. Although the vulnerability does not compromise confidentiality or integrity, the denial of service effect could be leveraged in targeted attacks to disrupt communications during critical periods. The medium severity rating reflects the limited scope of impact but acknowledges the potential for significant operational disruption in environments with high dependency on cellular connectivity.

Organizations should prioritize applying the MediaTek patch MOLY01661195 to all affected devices and modems running Modem NR15 firmware. Network operators should monitor for unauthorized or rogue base stations within their coverage areas using radio frequency monitoring tools and anomaly detection systems to prevent attackers from establishing malicious access points. Deploying network-level protections such as base station authentication and integrity verification can reduce the risk of rogue base station connections. Device manufacturers and integrators should verify firmware versions and enforce update policies to ensure vulnerable modems are upgraded promptly. For critical infrastructure, implementing redundancy in communication channels and failover mechanisms can mitigate the impact of potential denial of service events. Security teams should also educate users and administrators about the risks of connecting to untrusted cellular networks and encourage vigilance for unusual connectivity issues. Finally, collaboration with telecom providers to share threat intelligence on rogue base station activity can enhance detection and response capabilities.