CVE-2021-46901
📋 TL;DR
CVE-2021-46901 is a stack-based buffer overflow vulnerability in CETIC-6LBR's HTTP server component that allows remote attackers to execute arbitrary code or cause denial of service by sending specially crafted long URL requests over 6LoWPAN networks. This affects systems running CETIC-6LBR version 1.5.0 with the 6lbr-webserver component enabled. The vulnerability is particularly concerning for IoT deployments using 6LoWPAN networking.
💻 Affected Systems
- CETIC-6LBR (6lbr)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, allowing attackers to take control of the 6LBR device, pivot to other network segments, or disrupt critical IoT operations.
Likely Case
Denial of service causing the 6LBR device to crash or become unresponsive, disrupting IoT network connectivity and data collection.
If Mitigated
Limited impact with proper network segmentation and input validation, potentially causing only temporary service disruption.
🎯 Exploit Status
Exploitation requires network access to the 6LoWPAN interface but no authentication. The strcat vulnerability makes exploitation straightforward for attackers with basic buffer overflow knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after commit c3092a1ccc6b6b0e668f33f6f4b2d6967975d664
Vendor Advisory: https://github.com/cetic/6lbr/issues/414
Restart Required: Yes
Instructions:
1. Update to latest CETIC-6LBR version from GitHub repository
2. Rebuild the 6lbr-webserver component
3. Restart the 6LBR service
4. Verify the fix by checking the httpd.c file for proper bounds checking
🔧 Temporary Workarounds
Disable 6lbr-webserver
linuxDisable the vulnerable HTTP server component if not required
# Disable in configuration or remove webserver component
Network Segmentation
allRestrict 6LoWPAN network access to trusted devices only
# Configure firewall rules to limit 6LoWPAN traffic
🧯 If You Can't Patch
- Implement strict network access controls to limit 6LoWPAN traffic to trusted sources only
- Deploy network-based intrusion detection to monitor for long URL requests and buffer overflow attempts
🔍 How to Verify
Check if Vulnerable:
Check if running CETIC-6LBR version 1.5.0 with 6lbr-webserver enabled and examine httpd.c line 119 for unsafe strcat usageCheck Version:
Check 6LBR version in configuration files or via system logsVerify Fix Applied:
Verify the httpd.c file contains proper bounds checking (e.g., using strncat instead of strcat) and check version is updated📡 Detection & Monitoring
Log Indicators:
- HTTP server crashes
- Unusually long URL requests in logs
- Stack overflow error messages
Network Indicators:
- Multiple long URL requests over 6LoWPAN
- Patterns of buffer overflow exploitation attempts
SIEM Query:
source="6lbr-webserver" AND (url_length>1000 OR message="stack overflow" OR message="segmentation fault")🔗 References
- https://github.com/cetic/6lbr/blob/c3092a1ccc6b6b0e668f33f6f4b2d6967975d664/examples/6lbr/apps/6lbr-webserver/httpd.c#L119
- https://github.com/cetic/6lbr/issues/414
- https://github.com/cetic/6lbr/blob/c3092a1ccc6b6b0e668f33f6f4b2d6967975d664/examples/6lbr/apps/6lbr-webserver/httpd.c#L119
- https://github.com/cetic/6lbr/issues/414
