Overview

CVE-2026-20499 is a vulnerability in the MediaTek modem that could lead to remote escalation of privilege. This issue arises from a missing bounds check, which allows an attacker to potentially exploit the vulnerability if a user equipment (UE) connects to a rogue base station controlled by the attacker. The vulnerability has a CVSS score of 7.5 and is considered a high-severity issue.

Understanding the Vulnerability / Threat

Root Cause Analysis

The root cause of this vulnerability is a missing bounds check in the MediaTek modem software. This flaw belongs to the CWE-787 category, which involves out-of-bounds writes. The vulnerability occurs because the modem does not properly validate input data, allowing an attacker to write data outside the bounds of a buffer.

Attack Surface & Vector

The attack surface for this vulnerability is the communication interface between the UE and the base station. An attacker would need to control a rogue base station to exploit this vulnerability. The attack vector involves the UE connecting to this rogue base station, which triggers the out-of-bounds write due to the missing bounds check.

Exploitation Mechanics — Scenario Walkthrough

Scenario: Compromising a Device via a Rogue Base Station

Initial Position: An attacker sets up a rogue base station in a location where they can force a UE to connect to it, possibly by jamming or spoofing legitimate base station signals.

Triggering the Flaw: When a UE connects to the rogue base station, the attacker sends malformed data that exploits the missing bounds check in the MediaTek modem. This malformed data is crafted to exceed the buffer bounds, leading to an out-of-bounds write.

What Breaks: The security boundary that fails is the input validation and bounds checking mechanism in the modem software. This allows the attacker to execute arbitrary code on the UE.

Attacker's Prize: After successfully exploiting the vulnerability, the attacker gains remote escalation of privilege. This means they can execute commands on the UE without needing any additional execution privileges, potentially leading to data theft, lateral movement, or other malicious activities.

Real-World Impact

The real-world impact of this vulnerability can be significant. An attacker could exploit this vulnerability to gain unauthorized access to devices connected to the rogue base station. This could lead to various malicious activities, including data exfiltration, device takeover, or even spreading malware. The affected devices include various MediaTek chipsets used in smartphones and other connected devices.

Detection & Defense

Immediate Mitigations

The recommended immediate mitigation is to apply the patch provided by MediaTek, identified as Patch ID: MOLY01857954. Affected versions include multiple MediaTek chipsets (e.g., MT2716, MT2735, MT2737, etc.); users should upgrade to a patched version. Specific patched versions are not provided in the source data, so checking with the vendor or tracking CVE updates is necessary.

Detection Strategies

Detection strategies may involve monitoring for unusual activity from devices that have connected to potentially rogue base stations. This could include analyzing network traffic for anomalies or implementing security measures that detect and block connections to known rogue base stations. Specific log patterns or SIEM rules would depend on the network architecture and the devices in use.

Long-Term Hardening

Long-term hardening strategies include implementing robust security measures for devices and networks. This could involve enhancing authentication and authorization for base station connections, improving input validation for modem software, and regularly updating and patching devices. Architectural changes might include adopting more secure communication protocols or enhancing the security of the modem software development lifecycle.

Key Takeaways

  • CVE-2026-20499 is a high-severity vulnerability in MediaTek modems that allows for remote escalation of privilege.
  • The vulnerability is due to a missing bounds check, which can be exploited by connecting to a rogue base station.
  • No user interaction or additional execution privileges are needed for exploitation.
  • Applying the provided patch (Patch ID: MOLY01857954) is crucial for mitigation.
  • Detection and defense strategies involve monitoring network traffic and implementing robust security measures.

Sources