CVE-2026-7422: FreeRTOS-Plus-TCP Auth Bypass Vulnerability

CVE-2026-7422 Overview

Insufficient packet validation in FreeRTOS-Plus-TCP before V4.2.6 and V4.4.1 allows an adjacent network actor to bypass all checksum and minimum-size validation by spoofing the Ethernet source MAC address to match one of the device's own registered endpoints. The vulnerability exists because the loopback detection mechanism skips all input validation for packets whose source MAC matches a local endpoint, creating a dangerous bypass of critical security controls.

Critical Impact
An attacker on an adjacent network can inject malicious packets with spoofed MAC addresses, bypassing all checksum and size validation checks in the FreeRTOS-Plus-TCP stack, potentially leading to data integrity compromise in IoT and embedded systems.

Affected Products

FreeRTOS-Plus-TCP versions prior to V4.2.6
FreeRTOS-Plus-TCP versions prior to V4.4.1

Discovery Timeline

April 29, 2026 - CVE-2026-7422 published to NVD
April 29, 2026 - Last updated in NVD database

Technical Details for CVE-2026-7422

Vulnerability Analysis

This vulnerability stems from a flaw in the loopback detection logic within the FreeRTOS-Plus-TCP networking stack. When the TCP/IP stack receives an incoming packet, it performs a check to determine if the packet originated from the local device (loopback traffic). This check compares the source MAC address of the incoming packet against MAC addresses registered to the device's own network endpoints.

The critical flaw is that when a match is detected (indicating potential loopback traffic), the stack immediately bypasses all subsequent validation steps, including checksum verification and minimum packet size validation. While this optimization may have been intended to improve performance for legitimate local traffic, it creates a significant attack surface.

An attacker positioned on an adjacent network segment can observe the target device's MAC address and craft malicious packets with the source MAC field spoofed to match the victim's endpoint MAC address. These crafted packets will pass through the loopback detection check and proceed through the network stack without proper validation. This weakness is classified as CWE-290 (Authentication Bypass by Spoofing).

Root Cause

The root cause is a design flaw in the packet processing pipeline where the loopback detection mechanism serves as a gate that controls whether subsequent validation routines execute. The logic incorrectly assumes that packets with a matching source MAC address must be trusted internal traffic, when in reality MAC addresses can be trivially spoofed by any device on the same Layer 2 network segment.

This represents an Authentication Bypass by Spoofing (CWE-290) vulnerability where the packet's source MAC address is improperly used as an authentication mechanism. MAC addresses are not cryptographically secured and should never be relied upon as a trust boundary for security decisions.

Attack Vector

The attack requires adjacent network access, meaning the attacker must be on the same local network segment as the target FreeRTOS device. The attack flow involves:

The attacker monitors network traffic to identify the target device's MAC address
The attacker crafts malicious packets with intentionally corrupted checksums or invalid sizes
The attacker sets the source MAC address field to match the target device's own MAC address
When the target receives these packets, the loopback detection logic identifies the source MAC as local
All validation is skipped, and malformed packets are processed by higher-level protocol handlers

Since no code examples are available from verified sources, the vulnerability mechanism centers on the conditional logic in the packet reception path that checks if (source_mac == local_endpoint_mac) and subsequently sets flags to skip validation. For detailed technical analysis, refer to the GitHub Security Advisory GHSA-jpw4-6h59-62w9.

Detection Methods for CVE-2026-7422

Indicators of Compromise

Network traffic showing packets with source MAC addresses matching the device's own MAC address arriving from external interfaces
Malformed packets (incorrect checksums or invalid sizes) being processed by the network stack without rejection
Unexpected behavior in application-layer protocols due to processing of corrupted packet payloads
Log entries indicating packet handling anomalies that would normally be caught by validation routines

Detection Strategies

Deploy network monitoring to detect packets with spoofed source MAC addresses matching known device endpoints
Implement port security features on network switches to restrict MAC address spoofing on adjacent network segments
Monitor for abnormal traffic patterns where packets appear to originate from the receiving device itself
Use network intrusion detection systems (NIDS) with rules to flag MAC address anomalies

Monitoring Recommendations

Enable verbose logging on FreeRTOS devices where available to capture packet processing decisions
Monitor network switches for MAC address violations and port security alerts
Implement continuous network traffic analysis to detect spoofed MAC address patterns
Review application logs for symptoms of processing malformed data that should have been rejected

How to Mitigate CVE-2026-7422

Immediate Actions Required

Upgrade FreeRTOS-Plus-TCP to version V4.2.6 or V4.4.1 immediately
Isolate vulnerable FreeRTOS devices on dedicated network segments to limit adjacent network exposure
Implement network switch port security features to prevent MAC address spoofing
Conduct an inventory of all devices running affected FreeRTOS-Plus-TCP versions

Patch Information

The vulnerability has been addressed in FreeRTOS-Plus-TCP versions V4.2.6 and V4.4.1. Users should upgrade to these fixed versions as soon as possible. Patches are available through the official FreeRTOS GitHub releases:

Additional details are available in the AWS Security Bulletin 2026-021 and the GitHub Security Advisory GHSA-jpw4-6h59-62w9.

Workarounds

Implement network segmentation to isolate FreeRTOS devices from untrusted adjacent network devices
Enable MAC address filtering and port security on network switches to prevent spoofing attacks
Deploy intrusion detection systems to monitor for MAC address spoofing attempts
Consider disabling direct network exposure where possible by placing devices behind firewalls or gateways

bash

# Network switch port security example (Cisco IOS)
interface GigabitEthernet0/1
  switchport port-security
  switchport port-security maximum 1
  switchport port-security violation restrict
  switchport port-security mac-address sticky