CVE-2021-3321
📋 TL;DR
This CVE describes an integer underflow vulnerability in Zephyr's IEEE 802.15.4 fragment reassembly header removal code. When exploited, it can lead to buffer overflow, potentially allowing remote code execution or denial of service. Affects Zephyr RTOS users implementing IEEE 802.15.4 wireless networking.
💻 Affected Systems
- Zephyr RTOS
📦 What is this software?
Zephyr by Zephyrproject
⚠️ Risk & Real-World Impact
Worst Case
Remote attacker gains arbitrary code execution on affected Zephyr devices, potentially taking full control of IoT/embedded systems.
Likely Case
Denial of service through system crashes or instability in affected wireless networking functionality.
If Mitigated
Limited impact with proper network segmentation and device isolation, potentially only affecting specific wireless functionality.
🎯 Exploit Status
Requires sending specially crafted IEEE 802.15.4 packets to trigger the integer underflow during fragment reassembly.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in Zephyr v2.5.0 and later
Vendor Advisory: https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-w44j-66g7-xw99
Restart Required: Yes
Instructions:
1. Update Zephyr RTOS to version 2.5.0 or later. 2. Rebuild and redeploy firmware to affected devices. 3. Verify IEEE 802.15.4 functionality post-update.
🔧 Temporary Workarounds
Disable IEEE 802.15.4 Fragment Reassembly
allDisable fragment reassembly in IEEE 802.15.4 configuration if not required for your application.
Set CONFIG_IEEE802154_FRAGMENT_REASSEMBLY=n in prj.conf
Network Segmentation
allIsolate IEEE 802.15.4 networks from untrusted networks and implement strict firewall rules.
🧯 If You Can't Patch
- Implement strict network segmentation for IEEE 802.15.4 traffic
- Deploy network monitoring for anomalous IEEE 802.15.4 packet patterns
🔍 How to Verify
Check if Vulnerable:
Check Zephyr version and IEEE 802.15.4 configuration: if version >=2.4.0 and CONFIG_IEEE802154_FRAGMENT_REASSEMBLY=y, system is vulnerable.Check Version:
Check Zephyr version in build configuration or use Zephyr shell command 'kernel version' if available.Verify Fix Applied:
Verify Zephyr version is >=2.5.0 and check that IEEE 802.15.4 functionality works correctly after update.📡 Detection & Monitoring
Log Indicators:
- Kernel panics
- IEEE 802.15.4 subsystem crashes
- Unexpected reboots
Network Indicators:
- Malformed IEEE 802.15.4 fragments
- Unusual fragment reassembly patterns
SIEM Query:
Search for: (event_source:"zephyr_kernel" AND (event_type:"panic" OR event_type:"crash")) OR (protocol:"802.15.4" AND fragment_count > threshold)