CVE-2026-20503 Denial of service in MediaTek chipset

Medium 5.3 Published 7 Sep 2026 Updated 7 Sep 2026

A missing bounds check in MediaTek modem firmware allows remote attackers to cause a system crash via a rogue base station.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-20503?

CVE-2026-20503 is a medium-severity denial of service vulnerability in MediaTek, Inc. MediaTek chipset, published on 7 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In Modem, there is a possible system crash due to a missing bounds check. This could lead to remote denial of service, if a UE has connected to a rogue base station controlled by the attacker, with no additional execution privileges needed. User interaction is not needed for exploitation. Patch ID: MOLY01371002; Issue ID: MSV-9020.

Weakness: CWE-617

Which versions are affected by CVE-2026-20503?

It affects 57 products.

Products include Mediatek Mt2716 Firmware, Mediatek Mt2735 Firmware, Mediatek Mt2737 Firmware, Mediatek Mt6813 Firmware, Mediatek Mt6833 Firmware, Mediatek Mt6835 Firmware and 51 more.

How do I fix CVE-2026-20503?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-20503 being exploited?

There is no known exploitation of CVE-2026-20503 in the wild and no public exploit code.

Sources

Also known as A-528211067, ASB-A-528211067, GHSA-x74h-78mc-6jq7, M-MOLY01371002.