^{CVE-2021-37604:}Microchip MiWi Software Frame Counter Validation Vulnerability

Overview

This vulnerability (CVE-2021-37604) affects the Microchip MiWi wireless protocol stack, which is commonly used in IoT and embedded devices for sub-GHz wireless communications. The issue stems from an improper sequence of operations in the protocol implementation where frame counter validation occurs before message authentication. This incorrect sequence creates two significant security issues:

1. An attacker can inject messages with artificially high frame counter values and invalid payloads, causing legitimate devices to update their frame counter expectations. This can lead to denial of service as legitimate messages with normal frame counter values would then be rejected as "old" or "replayed."

2. The vulnerability also enables potential replay attacks against the network, where previously captured valid messages could be retransmitted and accepted by receiving devices.

This vulnerability is categorized as CWE-670 (Always-Incorrect Control Flow Implementation), reflecting how the improper sequence of security checks fundamentally undermines the protocol's security model.

Remediation

Users of Microchip MiWi software should take the following actions:

1. Update to the latest version of the Advanced Software Framework (ASF) that contains the patched MiWi implementation. The fixed version is available in ASF 3.50.0.100 or later.

2. If immediate updating is not possible, consider implementing additional security controls at the application layer to validate message authenticity and freshness.

3. Monitor network traffic for unusual patterns that might indicate exploitation attempts, such as sudden increases in frame counter values or unexpected communication patterns.

4. For critical deployments, consider implementing network segmentation to isolate MiWi-based devices from potential attackers.

5. Consult the Microchip MiWi Software Vulnerability Response page for specific guidance related to your implementation.

References

1. ASF Release Notes 3.50.0.100: https://ww1.microchip.com/downloads/en/DeviceDoc/asf-release-notes-3.50.0.100-readme.pdf

2. Advanced Software Framework Downloads: https://www.microchip.com/en-us/development-tools-tools-and-software/libraries-code-examples-and-more/advanced-software-framework-for-sam-devices#Downloads

3. MiWi Software Vulnerability Response: https://www.microchip.com/en-us/products/wireless-connectivity/software-vulnerability-response/miwi-software-vulnerability

4. MiWi Protocol Information: https://www.microchip.com/en-us/products/wireless-connectivity/sub-ghz/miwi-protocol

5. Microchip Product Change Notifications: https://www.microchip.com/product-change-notifications/#/