CVE-2025-20791 is a vulnerability identified in several MediaTek modem chipsets (including MT2735, MT6833 series, MT6853 series, MT6873 series, MT6880 series, MT6890 series, MT8675, MT8771, MT8791 series, and MT8797) that affects the modem firmware version NR15. The root cause is an incorrect error handling mechanism that leads to a reachable assertion failure within the modem's software. When a user equipment (UE) device equipped with these chipsets connects to a rogue base station controlled by an attacker, the assertion can be triggered, causing the modem system to crash. This results in a denial of service condition, disrupting the device's ability to maintain network connectivity. The vulnerability requires no additional execution privileges and does not need user interaction, making it remotely exploitable by an attacker who can set up a malicious base station. This attack vector is particularly concerning because rogue base stations can be deployed in proximity to targets without their knowledge. The flaw is categorized under CWE-617 (Reachable Assertion), indicating that the software does not properly validate conditions before asserting, leading to unexpected termination. Although no exploits have been reported in the wild, the vulnerability is published and patches are expected from MediaTek under Patch ID MOLY01661189. The broad range of affected chipsets suggests a wide impact across many mobile devices using MediaTek modems, including smartphones and IoT devices. The vulnerability primarily impacts availability by causing system crashes and potential service outages. Confidentiality and integrity impacts are not indicated. The lack of a CVSS score necessitates an assessment based on the technical details and potential impact.

For European organizations, the primary impact of CVE-2025-20791 is the potential disruption of mobile communications due to modem crashes caused by rogue base stations. This can affect critical sectors such as telecommunications providers, emergency services, transportation, and enterprises relying on mobile connectivity for operations. Denial of service at the device level can lead to loss of communication, impacting business continuity and safety-critical functions. The vulnerability could also be exploited in targeted attacks against high-value individuals or organizations by deploying rogue base stations in strategic locations. Given the increasing reliance on mobile devices and IoT in Europe, widespread exploitation could degrade network reliability and user trust. Additionally, industries with mobile-dependent infrastructure, such as smart cities and industrial automation, may face operational risks. Although no data breach or code execution is involved, the availability impact alone can have significant operational and reputational consequences. The threat is heightened by the ease of exploitation and lack of user interaction requirements.

1. Apply official patches from MediaTek as soon as they are released (Patch ID MOLY01661189). Coordinate with device manufacturers and mobile operators to ensure timely firmware updates. 2. Mobile network operators should monitor for and mitigate rogue base stations by deploying detection systems that identify unauthorized or suspicious base stations in their coverage areas. 3. Enterprises should implement mobile device management (MDM) solutions to enforce firmware updates and monitor device health. 4. Users and organizations should avoid connecting to untrusted or unknown cellular networks, especially in sensitive environments. 5. Security teams should collaborate with telecom providers to share threat intelligence regarding rogue base station activities. 6. For critical infrastructure, consider network segmentation and fallback communication channels to reduce reliance on vulnerable mobile devices. 7. Encourage manufacturers to improve error handling and assertion checks in modem firmware to prevent similar vulnerabilities. 8. Conduct regular security assessments of mobile devices and IoT endpoints using affected chipsets to identify unpatched systems.