CVE-2025-20703 Overview
CVE-2025-20703 is an out-of-bounds read vulnerability [CWE-125] in the MediaTek Modem component. The flaw stems from an incorrect bounds check that attackers can trigger when a user equipment (UE) connects to a rogue base station. Successful exploitation causes a remote denial of service (DoS) on the affected device without requiring user interaction or elevated privileges. The vulnerability is tracked by MediaTek under Patch ID MOLY01599794 and Issue ID MSV-3708. MediaTek addressed the issue in the September 2025 Product Security Bulletin. The vulnerability affects a wide range of 4G/5G modem chipsets used in smartphones, tablets, and connected devices.
Critical Impact
An adjacent-network attacker operating a rogue base station can crash the modem of any vulnerable UE within radio range, disrupting cellular connectivity without authentication or user interaction.
Affected Products
- MediaTek 5G modem platforms: NR15, NR16, NR17, NR17R
- MediaTek smartphone SoCs including MT6833, MT6853, MT6873, MT6885, MT6893, MT6895, MT6983, MT6985, MT6989, MT6991
- MediaTek automotive and tablet SoCs including MT2735, MT2737, MT8673, MT8675, MT8791, MT8798, MT8893
Discovery Timeline
- 2025-09-01 - CVE-2025-20703 published to NVD
- 2025-09 - MediaTek releases security patch via September 2025 Product Security Bulletin
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-20703
Vulnerability Analysis
The vulnerability resides in the MediaTek Modem firmware that processes cellular protocol messages between the UE and the base station. An incorrect bounds check in the message parsing path allows a specially crafted radio frame to trigger an out-of-bounds read beyond an allocated buffer. The read operation accesses memory outside the intended range, causing the modem baseband to crash. Because the modem handles all cellular connectivity, the crash results in loss of voice, SMS, and data services on the affected device. Exploitation requires only adjacent network access through radio proximity, with no credentials or user interaction. The vulnerability is categorized under CWE-125 (Out-of-Bounds Read) and impacts availability but not confidentiality or integrity.
Root Cause
The root cause is an incorrect bounds check in a cellular protocol handler within the Modem firmware. When processing attacker-controlled fields from a radio message, the component fails to properly validate length or offset values before reading from a buffer. This allows reads past the end of the allocated memory region, producing undefined behavior that terminates modem execution.
Attack Vector
Exploitation requires an attacker to operate a rogue base station within radio range of a vulnerable UE. Modern cellular devices typically attempt to connect to the strongest available cell, and an attacker with low-cost software-defined radio hardware can impersonate a legitimate base station. Once the UE associates with the rogue cell, the attacker sends a crafted downlink message that triggers the out-of-bounds read in the modem. No prior pairing, user interaction, or privileges are required. See the MediaTek Product Security Bulletin for additional protocol context.
No verified proof-of-concept code is publicly available. The vulnerability mechanism involves protocol-level parsing within the modem baseband, and MediaTek has not released exploitation details.
Detection Methods for CVE-2025-20703
Indicators of Compromise
- Unexpected modem resets, baseband crashes, or loss of cellular registration on MediaTek-powered devices
- Repeated cellular reconnection attempts correlated with the presence of an unknown or unauthorized base station
- Device logs showing modem subsystem restarts (ssr, mdm_restart) without a corresponding software update or configuration change
Detection Strategies
- Monitor fleet mobile device management (MDM) telemetry for abnormal rates of cellular disconnections or modem reboots across devices with MediaTek chipsets
- Deploy mobile threat defense agents that can flag connections to suspicious or rogue cell towers (unexpected PLMN, cell ID, or signal profile)
- Correlate device-side modem crash reports with physical location data to identify clusters indicating a localized rogue base station
Monitoring Recommendations
- Track MediaTek chipset firmware versions across the device inventory and verify patch status against the September 2025 bulletin
- Enable logging of radio-layer events on managed devices where supported, and ingest into centralized telemetry
- Alert on devices that exhibit repeated modem subsystem restarts within short intervals
How to Mitigate CVE-2025-20703
Immediate Actions Required
- Apply the vendor firmware update containing MediaTek Patch ID MOLY01599794 as soon as the device OEM distributes it
- Inventory affected devices by MediaTek chipset model and prioritize patching for high-value or executive devices
- Instruct users to avoid connecting to unknown or weak-signal cellular networks in sensitive locations
Patch Information
MediaTek released the fix for CVE-2025-20703 in the September 2025 Product Security Bulletin under Patch ID MOLY01599794 and Issue ID MSV-3708. The patch must be integrated by downstream device manufacturers (OEMs) and delivered to end users through vendor firmware updates. Confirm the applicable Android security patch level or OEM firmware revision that incorporates the fix.
Workarounds
- Where supported by the device, disable automatic connection to 2G/legacy networks to reduce exposure to protocol downgrade and rogue cell scenarios
- Enable airplane mode in untrusted radio environments until the device firmware is updated
- For managed fleets, restrict operation to known cellular carriers through carrier allow-lists where the MDM platform supports it
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
