CVE-2021-27255
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to execute arbitrary code with root privileges on NETGEAR R7800 routers. The flaw exists in the refresh_status.aspx endpoint which doesn't require authentication to start services. Only NETGEAR R7800 routers running firmware version 1.0.2.76 are affected.
💻 Affected Systems
- NETGEAR R7800
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router with root-level code execution, allowing attackers to intercept all network traffic, install persistent malware, pivot to internal networks, or brick the device.
Likely Case
Router takeover leading to DNS hijacking, credential theft from network traffic, and installation of backdoors for persistent access.
If Mitigated
No impact if patched or if router is behind proper network segmentation and firewalls.
🎯 Exploit Status
ZDI published detailed advisory with exploitation details. No authentication required makes exploitation trivial.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware version 1.0.2.78 or later
Vendor Advisory: https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to Advanced > Administration > Firmware Update. 3. Check for updates or manually download firmware from NETGEAR support site. 4. Upload and install firmware version 1.0.2.78 or later. 5. Reboot router after installation.
🔧 Temporary Workarounds
Disable remote management
allPrevent external access to router management interface
Navigate to Advanced > Administration > Remote Management and disable
Network segmentation
allPlace router in isolated network segment with strict firewall rules
🧯 If You Can't Patch
- Replace affected router with patched model or different vendor
- Implement strict network segmentation and firewall rules to limit router exposure
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via admin interface at Advanced > Administration > Firmware UpdateCheck Version:
Not applicable - check via web interfaceVerify Fix Applied:
Verify firmware version is 1.0.2.78 or later in router admin interface📡 Detection & Monitoring
Log Indicators:
- Unusual requests to refresh_status.aspx endpoint
- Unexpected service startups
- Failed authentication attempts to management interface
Network Indicators:
- External IP addresses accessing router management ports
- Unusual outbound connections from router
SIEM Query:
source_ip=external AND dest_port=80,443 AND uri_path="*refresh_status.aspx*"🔗 References
- https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
- https://www.zerodayinitiative.com/advisories/ZDI-21-263/
- https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
- https://www.zerodayinitiative.com/advisories/ZDI-21-263/
