CVE-2025-20703 is a high-severity vulnerability classified as CWE-125 (Out-of-bounds Read) affecting a broad range of MediaTek modem chipsets, including models MT2735 through MT8893 and their variants. The flaw resides in the modem's firmware, specifically in the bounds checking logic. An incorrect bounds check allows an attacker controlling a rogue base station to induce an out-of-bounds read condition remotely. This vulnerability does not require any user interaction or prior authentication, making it remotely exploitable by simply having a User Equipment (UE) device connect to the malicious base station. The primary impact of this flaw is a denial of service (DoS) condition, which can disrupt the modem's normal operation, potentially causing the device to crash or reboot. The vulnerability affects modem firmware versions NR15, NR16, NR17, and NR17R. The CVSS v3.1 base score is 7.5, indicating a high severity level, with an attack vector of network (remote), low attack complexity, no privileges required, no user interaction, and impact limited to availability (no confidentiality or integrity impact). There are no known exploits in the wild as of the publication date (September 1, 2025), and no patch links were provided, though MediaTek has assigned an internal patch ID (MOLY01599794) and issue ID (MSV-3708). The vulnerability affects a wide range of MediaTek modems commonly used in mobile devices, IoT gateways, and embedded communication modules, which are integral to cellular connectivity.

For European organizations, the impact of CVE-2025-20703 can be significant, especially for those relying on devices with MediaTek modems for critical communications infrastructure, mobile workforce connectivity, or IoT deployments. The vulnerability enables attackers to cause denial of service remotely by setting up rogue base stations, which could disrupt cellular connectivity for affected devices. This disruption can lead to loss of communication, impacting business operations, emergency services, and critical infrastructure monitoring. Enterprises using mobile broadband for remote sites or mobile employees may experience outages, affecting productivity and operational continuity. Additionally, sectors such as transportation, healthcare, and utilities that increasingly depend on cellular IoT devices could face service interruptions. The lack of confidentiality or integrity impact reduces the risk of data breaches, but availability disruption alone can have cascading effects on dependent systems and services. Given the ease of exploitation and no user interaction requirement, the threat is particularly concerning in urban or high-density areas where rogue base stations can be deployed covertly.

To mitigate this vulnerability effectively, European organizations should: 1) Identify and inventory all devices using affected MediaTek modem chipsets and firmware versions NR15 through NR17R. 2) Engage with device manufacturers and vendors to obtain and apply firmware updates or patches as soon as they become available from MediaTek or OEMs. 3) Implement network-level detection and prevention mechanisms to identify and block rogue base stations, such as using cellular network anomaly detection tools and SIM-based security features. 4) Employ mobile device management (MDM) solutions to monitor device connectivity and enforce security policies that can detect unusual network behavior indicative of rogue base station attacks. 5) For critical deployments, consider fallback communication methods or redundant connectivity options to maintain availability during potential outages. 6) Educate security teams about the threat of rogue base stations and incorporate this vulnerability into incident response plans. 7) Collaborate with mobile network operators to report and mitigate rogue base station activity in their coverage areas. These steps go beyond generic patching advice by emphasizing proactive detection, inventory management, and operational resilience.