CVE-2026-25139: RIOT OS Buffer Overflow Vulnerability

CVE-2026-25139 Overview

CVE-2026-25139 is an out-of-bounds read vulnerability affecting RIOT, an open-source microcontroller operating system designed for Internet of Things (IoT) devices and other embedded systems. The vulnerability exists in the 6LoWPAN stack implementation where multiple out-of-bounds read conditions allow any unauthenticated user with the ability to send or manipulate input packets to read adjacent memory locations or crash vulnerable devices.

Critical Impact

Unauthenticated remote attackers can exploit this vulnerability to crash IoT devices or potentially leak sensitive memory contents from devices running the vulnerable 6LoWPAN stack, posing significant risks to IoT infrastructure deployments.

Affected Products

• RIOT OS version 2025.10 and prior
• IoT devices running the 6LoWPAN network stack
• Embedded devices utilizing RIOT's networking implementation

Discovery Timeline

• 2026-02-04 - CVE-2026-25139 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-25139

Vulnerability Analysis

This vulnerability stems from improper input validation in RIOT's 6LoWPAN (IPv6 over Low-Power Wireless Personal Area Networks) stack implementation. The 6LoWPAN protocol is widely used in IoT environments to enable IPv6 communication over IEEE 802.15.4 wireless networks, making this vulnerability particularly concerning for smart home, industrial IoT, and sensor network deployments.

The core issue involves insufficient bounds checking when processing incoming network packets. When a packet is received by the 6LoWPAN stack, it is cast into a sixlowpan_sfr_rfrag_t struct and dereferenced without first validating that the packet contains sufficient data to populate the entire struct object. This allows attackers to trigger reads beyond the allocated packet buffer boundaries.

Root Cause

The root cause is classified as CWE-125 (Out-of-bounds Read). The vulnerability occurs because the code fails to validate that incoming packet data is large enough to contain the expected sixlowpan_sfr_rfrag_t structure before performing the type cast and subsequent memory access operations. This missing size validation check allows undersized packets to be processed as if they contained valid structure data, resulting in memory reads outside the intended buffer boundaries.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker positioned on the same network segment or with the ability to send crafted packets to the target device can exploit this vulnerability. The attacker crafts malicious 6LoWPAN packets that are smaller than the expected sixlowpan_sfr_rfrag_t structure size. When the vulnerable device processes these packets, it reads memory beyond the packet buffer, potentially exposing adjacent memory contents or causing the device to crash due to invalid memory access.

The attack can be executed by sending specially crafted fragmented IPv6 packets over the 6LoWPAN protocol. Since no authentication is required and the vulnerability exists in the network stack's packet processing path, any device capable of sending 6LoWPAN frames to the target can potentially exploit this flaw.

Detection Methods for CVE-2026-25139

Indicators of Compromise

• Unexpected device crashes or reboots in IoT devices running RIOT OS
• Abnormal 6LoWPAN packet patterns with undersized fragmentation headers
• Memory access violations or segmentation faults in device logs
• Unusual network traffic patterns targeting 6LoWPAN endpoints

Detection Strategies

• Monitor 6LoWPAN network traffic for malformed or undersized packet fragments
• Implement network intrusion detection rules to identify packets with invalid header sizes
• Deploy anomaly detection for IoT device behavior to catch crash-restart cycles
• Review device crash logs for memory access violation patterns indicative of out-of-bounds reads

Monitoring Recommendations

• Enable verbose logging on RIOT-based devices where possible to capture packet processing errors
• Implement network segmentation to isolate vulnerable IoT devices from untrusted networks
• Deploy network monitoring at the gateway level to inspect 6LoWPAN traffic before reaching endpoints
• Establish baseline behavior profiles for IoT devices to detect anomalous crash patterns

How to Mitigate CVE-2026-25139

Immediate Actions Required

• Identify all devices in your environment running RIOT OS version 2025.10 or prior
• Isolate vulnerable IoT devices from untrusted network segments using network segmentation
• Implement strict firewall rules to limit which hosts can send 6LoWPAN traffic to vulnerable devices
• Monitor the GitHub Security Advisory for patch availability updates

Patch Information

At the time of publication, no known patch exists for this vulnerability. Organizations should monitor the RIOT OS project's security advisories and GitHub repository for updates. The security advisory is tracked at GHSA-c8fh-23qr-97mc.

Workarounds

• Implement network-level filtering to block potentially malicious 6LoWPAN packets at the network perimeter
• Deploy vulnerable devices only on isolated network segments with strict access controls
• Use application-layer gateways that can validate 6LoWPAN packet integrity before forwarding
• Consider disabling unnecessary 6LoWPAN functionality if not required for device operation

# Network isolation configuration example for IoT segments
# Configure firewall rules to restrict access to vulnerable IoT devices
# Only allow trusted management hosts to communicate with 6LoWPAN devices
iptables -A FORWARD -d 192.168.100.0/24 -j DROP
iptables -A FORWARD -s 192.168.1.10 -d 192.168.100.0/24 -j ACCEPT