CVE-2026-7426 Overview
CVE-2026-7426 is a heap buffer overflow vulnerability in the IPv6 Router Advertisement (RA) processing logic of Amazon FreeRTOS-Plus-TCP. The flaw stems from insufficient validation of the prefix length field within incoming RA packets. An adjacent network attacker can send a crafted Router Advertisement containing a prefix length value that exceeds the maximum valid length, triggering memory corruption on the heap. The issue affects FreeRTOS-Plus-TCP versions prior to V4.2.6 and V4.4.1. Deployments that process only IPv4 RA traffic are not impacted. The vulnerability is tracked under [CWE-787] (Out-of-Bounds Write).
Critical Impact
An adjacent attacker on the same link-local network can corrupt heap memory on embedded devices running vulnerable FreeRTOS-Plus-TCP versions, leading to integrity and availability impact on connected IoT and embedded systems.
Affected Products
- Amazon FreeRTOS-Plus-TCP versions before V4.2.6
- Amazon FreeRTOS-Plus-TCP versions before V4.4.1
- Embedded and IoT devices using FreeRTOS-Plus-TCP with IPv6 enabled
Discovery Timeline
- 2026-04-29 - CVE-2026-7426 published to NVD
- 2026-05-04 - Last updated in NVD database
Technical Details for CVE-2026-7426
Vulnerability Analysis
The vulnerability resides in the IPv6 Router Advertisement parsing path of FreeRTOS-Plus-TCP. ICMPv6 Router Advertisement messages include a Prefix Information Option that carries a Prefix Length field. RFC 4861 limits this field to values between 0 and 128 bits, since IPv6 addresses are 128 bits wide. The vulnerable code path accepts the attacker-supplied prefix length without bounding it against this maximum. Subsequent memory operations use the unvalidated length value to write into a heap-allocated buffer, producing an out-of-bounds write.
Because FreeRTOS-Plus-TCP runs on resource-constrained embedded systems with limited memory protection, heap corruption can overwrite adjacent allocator metadata or live objects. The impact ranges from device crash and reboot to potential control-flow hijacking, depending on the heap layout and target build.
Root Cause
The root cause is missing input validation on the Prefix Length field of the Prefix Information Option in IPv6 Router Advertisements. The code path does not enforce the protocol-defined upper bound of 128 before using the value in size calculations or copy operations. This results in a classified out-of-bounds heap write under [CWE-787].
Attack Vector
Exploitation requires adjacent network access — the attacker must be on the same Layer 2 segment or link-local IPv6 domain as the target device. No authentication or user interaction is required. The attacker crafts an ICMPv6 Router Advertisement frame containing a Prefix Information Option with a prefix length greater than 128 and transmits it to the all-nodes multicast address or directly to the target. When the vulnerable RA handler processes the option, the oversized prefix length triggers the heap buffer overflow.
The vulnerability is described in prose only because no verified public proof-of-concept exploit code is available. Technical details are documented in the GitHub Security Advisory GHSA-97qg-4359-xm3x.
Detection Methods for CVE-2026-7426
Indicators of Compromise
- ICMPv6 Type 134 (Router Advertisement) packets containing Prefix Information Options with a Prefix Length value greater than 128.
- Unexpected reboots, watchdog resets, or task crashes on embedded devices running FreeRTOS-Plus-TCP after receiving IPv6 traffic.
- Anomalous RA traffic originating from non-router hosts on the local segment.
Detection Strategies
- Deploy network sensors that inspect ICMPv6 RA messages and alert on malformed Prefix Information Options with invalid prefix length values.
- Enable RA Guard on managed switches to drop Router Advertisements from unauthorized ports.
- Inventory embedded and IoT assets to identify firmware images linking against vulnerable FreeRTOS-Plus-TCP versions prior to V4.2.6 or V4.4.1.
Monitoring Recommendations
- Monitor link-local IPv6 segments for spikes in ICMPv6 Type 134 traffic from unexpected sources.
- Log device availability metrics and correlate unexpected restarts on FreeRTOS-based devices with adjacent network events.
- Capture and retain packet metadata on OT and IoT VLANs to support post-incident analysis.
How to Mitigate CVE-2026-7426
Immediate Actions Required
- Upgrade FreeRTOS-Plus-TCP to V4.2.6 or V4.4.1 and rebuild affected firmware images.
- Identify all deployed devices running vulnerable versions with IPv6 enabled and prioritize them for firmware update.
- Restrict adjacent network access to embedded devices by segmenting IoT and OT traffic onto isolated VLANs.
Patch Information
The FreeRTOS project released fixed versions V4.2.6 and V4.4.1 that add validation of the Prefix Length field during IPv6 Router Advertisement processing. Refer to the AWS Security Bulletin 2026-023 and the GitHub Security Advisory GHSA-97qg-4359-xm3x for upgrade guidance.
Workarounds
- Disable IPv6 support in FreeRTOS-Plus-TCP builds where it is not required; devices processing only IPv4 RA traffic are not impacted.
- Enable IPv6 RA Guard on access switches to filter Router Advertisements from untrusted ports.
- Place vulnerable devices behind a Layer 3 boundary that blocks ICMPv6 Type 134 messages from untrusted networks.
# Example: Cisco IOS RA Guard policy to drop RAs from host ports
ipv6 nd raguard policy HOST_PORTS
device-role host
interface range GigabitEthernet1/0/1 - 24
ipv6 nd raguard attach-policy HOST_PORTS
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
