CVE-2021-40406
📋 TL;DR
A denial of service vulnerability in Reolink RLC-410W cameras allows attackers to prevent legitimate users from logging in by sending specially-crafted HTTP requests to the cgiserver.cgi session creation functionality. This affects users of vulnerable Reolink camera models, potentially disrupting surveillance system access.
💻 Affected Systems
- Reolink RLC-410W
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Persistent denial of service preventing all legitimate user logins, effectively disabling camera management and monitoring capabilities until device restart or fix.
Likely Case
Temporary login disruption for legitimate users, requiring device restart to restore functionality.
If Mitigated
No impact if device is patched or network access is properly restricted.
🎯 Exploit Status
HTTP-based attack requiring no authentication, making exploitation straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Reolink for latest firmware updates
Vendor Advisory: https://reolink.com/support/
Restart Required: Yes
Instructions:
1. Log into Reolink camera web interface. 2. Navigate to System > Maintenance > Firmware Upgrade. 3. Download latest firmware from Reolink support site. 4. Upload and apply firmware update. 5. Reboot camera after update completes.
🔧 Temporary Workarounds
Network Segmentation
linuxRestrict network access to camera management interface
iptables -A INPUT -p tcp --dport 80 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
Access Control Lists
allImplement firewall rules to limit HTTP access to trusted IPs only
🧯 If You Can't Patch
- Isolate camera on separate VLAN with strict access controls
- Implement rate limiting on HTTP requests to cgiserver.cgi endpoint
🔍 How to Verify
Check if Vulnerable:
Check firmware version in camera web interface under System > Device InformationCheck Version:
curl -s http://camera-ip/cgi-bin/cgiserver.cgi?cmd=getSystemInfo | grep versionVerify Fix Applied:
Verify firmware version is updated beyond v3.0.0.136_20121102 and test login functionality📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts
- Unusual HTTP requests to cgiserver.cgi
- Session creation failures
Network Indicators:
- HTTP POST requests to /cgi-bin/cgiserver.cgi with malformed parameters
- High volume of requests to session endpoints
SIEM Query:
source="camera_logs" AND (uri="/cgi-bin/cgiserver.cgi" AND status=500) OR (event="session_creation_failed")