CVE-2021-27253
📋 TL;DR
This vulnerability allows network-adjacent attackers to bypass authentication and execute arbitrary code with root privileges on NETGEAR Nighthawk R7800 routers. The flaw exists in the handling of the rc_service parameter in apply_bind.cgi, where improper input validation enables command injection. Attackers on the same network can exploit this to take complete control of affected routers.
💻 Affected Systems
- NETGEAR Nighthawk R7800
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of router with root access, enabling traffic interception, malware deployment, network pivoting, and persistent backdoor installation.
Likely Case
Router takeover leading to DNS hijacking, credential theft from network traffic, and deployment of malware to connected devices.
If Mitigated
Limited to authenticated attackers on local network; proper network segmentation and access controls reduce exposure.
🎯 Exploit Status
Authentication bypass exists, making exploitation straightforward for network-adjacent attackers. Public exploit code available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware version 1.0.2.76 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 1.0.2.76+. 4. Upload and install update. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Disable remote administration
allPrevents exploitation by disabling web interface access from local network
Navigate to Advanced > Administration > Remote Management and disable
Network segmentation
allIsolate router management interface to trusted VLAN
🧯 If You Can't Patch
- Replace router with patched model or different vendor
- Implement strict network access controls to limit who can reach router management interface
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under Advanced > Administration > Firmware UpdateCheck Version:
curl -s http://routerlogin.com/currentsetting.htm | grep firmwareVerify Fix Applied:
Confirm firmware version is 1.0.2.76 or higher in admin interface📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /apply_bind.cgi with rc_service parameter
- Multiple failed authentication attempts followed by successful access
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains
- Unexpected SSH/Telnet connections from router
SIEM Query:
source="router.log" AND (uri="/apply_bind.cgi" AND rc_service=*) OR (event_type="authentication" AND result="success" AFTER result="failure")🔗 References
- https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
- https://www.zerodayinitiative.com/advisories/ZDI-21-249/
- https://kb.netgear.com/000062883/Security-Advisory-for-Multiple-Vulnerabilities-on-Some-Routers-Satellites-and-Extenders
- https://www.zerodayinitiative.com/advisories/ZDI-21-249/
