CVE-2021-3625
📋 TL;DR
CVE-2021-3625 is a heap-based buffer overflow vulnerability in Zephyr RTOS's USB Device Firmware Upgrade (DFU) DNLOAD functionality. This allows attackers to execute arbitrary code or cause denial of service by sending specially crafted USB packets. Affects Zephyr RTOS users with USB DFU enabled on devices running vulnerable versions.
💻 Affected Systems
- Zephyr RTOS
📦 What is this software?
Zephyr by Zephyrproject
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, persistence, and lateral movement within connected systems.
Likely Case
Denial of service causing device crashes or instability, potentially requiring physical reset.
If Mitigated
Limited impact if USB DFU is disabled or devices are not exposed to untrusted USB connections.
🎯 Exploit Status
Exploitation requires physical or logical USB access to the device.
🛠️ 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-c3gr-hgvr-f363
Restart Required: Yes
Instructions:
1. Update Zephyr RTOS to version 2.7.0 or later. 2. Rebuild and reflash firmware on affected devices. 3. Verify USB DFU functionality works correctly after update.
🔧 Temporary Workarounds
Disable USB DFU
allDisable USB Device Firmware Upgrade functionality in Zephyr configuration
CONFIG_USB_DFU=n in prj.conf or Kconfig
Restrict USB Access
allPhysically or logically restrict USB port access to trusted devices only
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable devices from critical systems
- Monitor USB connection logs and implement alerting for unauthorized USB activity
🔍 How to Verify
Check if Vulnerable:
Check Zephyr version and USB DFU configuration: grep -r CONFIG_USB_DFU in build directory and check Zephyr versionCheck Version:
Check Zephyr version in source code or build output: Zephyr version is typically defined in VERSION fileVerify Fix Applied:
Verify Zephyr version is >=2.7.0 and test USB DFU functionality with known good firmware📡 Detection & Monitoring
Log Indicators:
- USB DFU protocol errors
- Device resets/crashes during USB transfers
- Memory corruption warnings
Network Indicators:
- Unexpected USB device enumeration
- Abnormal USB traffic patterns
SIEM Query:
Device logs showing USB DFU failures OR device reboot events following USB connection