CVE-2021-3835
📋 TL;DR
This CVE describes a heap-based buffer overflow vulnerability in the USB device class implementation in Zephyr RTOS. Attackers could exploit this to execute arbitrary code or cause denial of service on affected systems. This affects devices running Zephyr RTOS version 2.6.0 and later.
💻 Affected Systems
- Zephyr RTOS
📦 What is this software?
Zephyr by Zephyrproject
Zephyr by Zephyrproject
Zephyr by Zephyrproject
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, potentially allowing attackers to take control of the device.
Likely Case
Denial of service through system crashes or instability when processing malicious USB data.
If Mitigated
Limited impact with proper input validation and memory protection mechanisms in place.
🎯 Exploit Status
Exploitation requires sending specially crafted USB data to vulnerable devices. No public exploit code has been identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in Zephyr v2.7.0 and later
Vendor Advisory: https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-fm6v-8625-99jf
Restart Required: Yes
Instructions:
1. Update Zephyr RTOS to version 2.7.0 or later. 2. Rebuild and redeploy firmware to affected devices. 3. Test USB functionality after update.
🔧 Temporary Workarounds
Disable USB device functionality
allTemporarily disable USB device support if not required for device operation
Modify device configuration to disable CONFIG_USB_DEVICE_STACK
Implement input validation
allAdd custom validation for USB data packets before processing
Implement bounds checking in USB device class handlers
🧯 If You Can't Patch
- Segment network to isolate USB-connected devices from untrusted networks
- Implement strict USB device whitelisting and monitoring
🔍 How to Verify
Check if Vulnerable:
Check Zephyr version: if >=2.6.0 and <2.7.0, device is vulnerableCheck Version:
Check Zephyr version in build configuration or device firmwareVerify Fix Applied:
Verify Zephyr version is >=2.7.0 and test USB functionality📡 Detection & Monitoring
Log Indicators:
- USB error messages
- System crashes during USB operations
- Memory corruption warnings
Network Indicators:
- Unusual USB traffic patterns
- Unexpected USB device enumeration
SIEM Query:
Search for USB-related error codes or system crashes in device logs