CVE-2026-20405 is a security vulnerability identified in multiple MediaTek modem chipsets, including models MT2735 through MT8893, affecting modem firmware versions NR15 through NR17R. The root cause is a missing bounds check in the modem’s code, leading to a reachable assertion failure (CWE-617). This flaw can be exploited remotely by an attacker who operates a rogue base station that a user equipment (UE) connects to, causing the modem to crash and resulting in a denial of service condition. No user interaction or elevated privileges are required, making exploitation straightforward once the UE connects to the malicious base station. The vulnerability impacts the modem’s stability and availability, potentially disrupting mobile communications on affected devices. MediaTek has acknowledged the issue and assigned internal patch IDs (MOLY01688495, MSV-4818), though no public patch links are provided yet. There are no known exploits in the wild at this time, but the broad range of affected chipsets and the nature of the vulnerability pose a significant risk. The vulnerability is particularly concerning for mobile devices used in critical infrastructure or enterprise environments where communication reliability is paramount. The lack of a CVSS score necessitates an independent severity assessment based on the technical details and potential impact.

For European organizations, the primary impact of CVE-2026-20405 is the potential for remote denial of service on mobile devices and embedded systems using affected MediaTek modems. This could disrupt mobile communications, affecting business operations, emergency services, and critical infrastructure relying on cellular connectivity. Enterprises with mobile workforces or IoT deployments using these chipsets may experience outages or degraded service. The vulnerability could also be exploited to target specific users or groups by deploying rogue base stations in strategic locations, leading to localized communication blackouts. Telecommunications providers and mobile network operators in Europe could face increased support costs and reputational damage if large numbers of subscribers are affected. Additionally, sectors such as transportation, healthcare, and public safety that depend on reliable mobile connectivity might see operational risks. The absence of required user interaction and the ease of triggering the vulnerability increase the threat level. However, the lack of known active exploits and the need for proximity to the victim device (to operate a rogue base station) somewhat limit the attack scope.

European organizations should prioritize the following mitigations: 1) Work closely with device manufacturers and vendors to ensure timely application of firmware updates and patches once publicly available from MediaTek or device OEMs. 2) Deploy network-level defenses to detect and block rogue base stations, including monitoring for anomalous base station behavior and using SIM-based or network-assisted detection mechanisms. 3) Educate users and IT staff about the risks of connecting to untrusted cellular networks, especially in high-risk or sensitive environments. 4) For critical infrastructure, consider multi-factor communication channels or fallback options to maintain connectivity if mobile networks are disrupted. 5) Collaborate with mobile network operators to enhance network authentication and integrity checks to prevent rogue base station attacks. 6) Implement device-level monitoring to detect abnormal modem behavior or frequent disconnections that may indicate exploitation attempts. 7) Maintain an inventory of devices using affected MediaTek chipsets to assess exposure and prioritize remediation efforts. These steps go beyond generic advice by focusing on both patch management and proactive network security controls tailored to the nature of this vulnerability.