CVE-2021-34947
📋 TL;DR
This is a critical remote code execution vulnerability in NETGEAR R7800 routers that allows network-adjacent attackers to execute arbitrary code as root without authentication. The vulnerability exists in the net-cgi component's parsing of soap_block_table files due to improper input validation leading to an out-of-bounds write. All users with affected NETGEAR R7800 routers are at risk.
💻 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 traffic, modify DNS settings, install persistent malware, pivot to internal networks, or brick the device.
Likely Case
Router takeover leading to man-in-the-middle attacks, credential theft, network surveillance, and potential lateral movement to connected devices.
If Mitigated
Limited impact if router is isolated from untrusted networks, though still vulnerable to compromised devices on the same network segment.
🎯 Exploit Status
Exploitation requires network adjacency but no authentication. The vulnerability is well-documented in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware version 1.0.2.84 or later
Vendor Advisory: https://kb.netgear.com/000064044/Security-Advisory-for-Pre-Authentication-Buffer-Overflow-on-Some-Routers-PSV-2021-0129
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 1.0.2.84+. 4. Upload and install the update. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Network Segmentation
allIsolate the router from untrusted devices by placing it on a separate VLAN or network segment
Disable Unnecessary Services
allDisable remote administration and any unnecessary network services if not required
🧯 If You Can't Patch
- Replace the router with a patched model or different vendor
- Implement strict network access controls to limit which devices can communicate with the router
🔍 How to Verify
Check if Vulnerable:
Check current firmware version in router admin interface under Advanced > Administration > Firmware UpdateCheck Version:
Not applicable - check via web interfaceVerify Fix Applied:
Verify firmware version is 1.0.2.84 or higher in the router admin interface📡 Detection & Monitoring
Log Indicators:
- Unusual SOAP requests to router management interface
- Multiple failed exploit attempts
- Unexpected process execution
Network Indicators:
- Unusual traffic patterns to router management ports
- Exploit-specific payloads in network traffic
SIEM Query:
source="router_logs" AND (soap_block_table OR net-cgi) AND (buffer_overflow OR out_of_bounds)🔗 References
- https://kb.netgear.com/000064044/Security-Advisory-for-Pre-Authentication-Buffer-Overflow-on-Some-Routers-PSV-2021-0129
- https://www.zerodayinitiative.com/advisories/ZDI-21-1116/
- https://kb.netgear.com/000064044/Security-Advisory-for-Pre-Authentication-Buffer-Overflow-on-Some-Routers-PSV-2021-0129
- https://www.zerodayinitiative.com/advisories/ZDI-21-1116/
