CVE-2021-3329
📋 TL;DR
CVE-2021-3329 is a critical vulnerability in the Zephyr RTOS Bluetooth HCI Host stack initialization that lacks proper input validation, allowing attackers to crash the Bluetooth stack via crafted packets. This affects devices running vulnerable versions of Zephyr RTOS with Bluetooth enabled. The high CVSS score reflects the potential for denial of service attacks on IoT and embedded systems.
💻 Affected Systems
- Zephyr RTOS
📦 What is this software?
Zephyr by Zephyrproject
Zephyr by Zephyrproject
Zephyr by Zephyrproject
Zephyr by Zephyrproject
⚠️ Risk & Real-World Impact
Worst Case
Complete Bluetooth stack crash leading to denial of service, potentially disrupting Bluetooth-dependent functionality in IoT devices, medical equipment, or industrial control systems.
Likely Case
Bluetooth service disruption requiring device reboot, affecting connectivity for Bluetooth peripherals and wireless communications.
If Mitigated
Minimal impact if Bluetooth is disabled or devices are properly segmented from untrusted networks.
🎯 Exploit Status
Exploitation requires sending specially crafted Bluetooth packets to trigger the validation flaw during stack initialization.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Zephyr RTOS 2.5.0 and later
Vendor Advisory: https://zephyrprojectsec.atlassian.net/browse/ZEPSEC-117
Restart Required: Yes
Instructions:
1. Update Zephyr RTOS to version 2.5.0 or later. 2. Rebuild and redeploy the firmware. 3. Restart affected devices to apply the updated firmware.
🔧 Temporary Workarounds
Disable Bluetooth
allTemporarily disable Bluetooth functionality if not required, preventing exploitation of the vulnerable stack.
Configure device to disable Bluetooth via device-specific commands or configuration files
Network Segmentation
allIsolate Bluetooth-enabled devices from untrusted networks to limit attack surface.
🧯 If You Can't Patch
- Implement strict network access controls to limit Bluetooth traffic to trusted sources only.
- Monitor for Bluetooth stack crashes and implement automated alerting for potential exploitation attempts.
🔍 How to Verify
Check if Vulnerable:
Check Zephyr RTOS version and verify if Bluetooth is enabled. Vulnerable if version < 2.5.0 with Bluetooth active.Check Version:
Check Zephyr version in build configuration or via device firmware version command specific to implementation.Verify Fix Applied:
Confirm Zephyr RTOS version is 2.5.0 or later and verify Bluetooth functionality operates normally without crashes.📡 Detection & Monitoring
Log Indicators:
- Bluetooth stack crash logs
- HCI initialization failure messages
- Unexpected Bluetooth service restarts
Network Indicators:
- Unusual Bluetooth packet patterns targeting initialization sequences
SIEM Query:
Search for logs containing 'bluetooth crash', 'HCI error', or 'stack initialization failed' from Zephyr devices.