CVE-2026-20540 Overview
CVE-2026-20540 is an out-of-bounds read vulnerability in MediaTek Modem firmware. The flaw stems from a missing bounds check [CWE-126] that allows a remote attacker to trigger a denial of service on affected user equipment (UE). Exploitation requires the UE to connect to a rogue base station controlled by the attacker, but no user interaction or additional execution privileges are required. MediaTek assigned patch ID MOLY01774038 and tracks the issue internally as MSV-8912.
Critical Impact
A remote attacker operating a rogue base station can crash the modem subsystem on a connected UE, disrupting cellular connectivity without user interaction.
Affected Products
- MediaTek Modem firmware (specific chipset models listed in the vendor bulletin)
- Android devices integrating affected MediaTek modem baseband
- See the MediaTek Security Bulletin - October 2026 for the complete chipset list
Discovery Timeline
- 2026-10-05 - CVE-2026-20540 published to NVD
- 2026-10-06 - Last updated in NVD database
Technical Details for CVE-2026-20540
Vulnerability Analysis
The vulnerability resides in the MediaTek Modem baseband firmware, which processes radio protocol messages received over the cellular air interface. A code path parsing attacker-controlled data fails to validate a length or index field before performing a memory read. The resulting out-of-bounds read [CWE-126] accesses memory beyond the intended buffer boundary.
When the modem reads unexpected or invalid memory contents, the baseband processor enters an unrecoverable state and crashes. This produces a denial of service condition affecting cellular connectivity on the targeted UE. Because exploitation occurs below the Android application layer, standard application sandboxing does not mitigate the issue.
Root Cause
The root cause is a missing bounds check in a modem message parsing routine. The affected code trusts length or offset fields supplied by the serving base station without verifying them against the actual size of the receive buffer. MediaTek addresses the defect by adding the missing validation in patch MOLY01774038.
Attack Vector
Exploitation requires the attacker to operate a rogue cellular base station within radio range of the target device. The attacker lures the UE into attaching to the rogue cell, then transmits a crafted protocol message containing malformed length or offset fields. On receipt, the modem performs the out-of-bounds read and crashes, interrupting voice and data service on the device. The attack complexity is rated high because the attacker must successfully stand up and attract devices to a rogue base station.
No verified public exploit code is available. Refer to the MediaTek Security Bulletin - October 2026 for additional technical context.
Detection Methods for CVE-2026-20540
Indicators of Compromise
- Unexpected modem crashes, reboots, or loss of cellular service on affected MediaTek-based devices
- Baseband error logs or ramdump artifacts referencing the vulnerable parsing routine
- Device logs showing attachment to unknown or unexpected cell IDs prior to the crash
Detection Strategies
- Monitor mobile device management (MDM) telemetry for repeated baseband resets or loss of cellular connectivity events
- Use cellular network survey tools to identify rogue base stations broadcasting in sensitive physical locations
- Correlate device crash reports with geolocation data to detect localized exploitation attempts
Monitoring Recommendations
- Enable Android bug report collection on managed devices to capture modem crash traces
- Deploy IMSI catcher detection applications on high-risk user devices
- Track MediaTek security bulletin publications and map chipset identifiers to the managed device inventory
How to Mitigate CVE-2026-20540
Immediate Actions Required
- Identify all managed devices using affected MediaTek modem chipsets by consulting the October 2026 bulletin
- Prioritize firmware updates for devices operated in sensitive locations or by high-risk personnel
- Advise users to avoid connecting to unknown cellular networks and to enable 5G-only or LTE-only modes where supported
Patch Information
MediaTek released the fix under patch ID MOLY01774038. The patch must be delivered to end-user devices by the device OEM through a system or firmware update. Consult the MediaTek Security Bulletin - October 2026 and the corresponding OEM security advisories for update availability on specific device models.
Workarounds
- Restrict device radios to trusted networks using carrier-managed configuration profiles where available
- Disable 2G fallback on devices that support the option to reduce rogue base station attack surface
- Use airplane mode in environments where rogue base station activity is suspected, until the patch is applied
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
