CVE-2021-34982
📋 TL;DR
This is a critical stack-based buffer overflow vulnerability in NETGEAR routers' httpd service that allows network-adjacent attackers to execute arbitrary code as root without authentication. It affects multiple NETGEAR router models when parsing strings files. Attackers on the same network can exploit this to gain complete control of affected devices.
💻 Affected Systems
- NETGEAR R6400v2
- NETGEAR R6700
- NETGEAR R6700v3
- NETGEAR R6900P
- NETGEAR R7000
- NETGEAR R7000P
- NETGEAR R7850
- NETGEAR R7900
- NETGEAR R8000
- NETGEAR RS400
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of router with root privileges, allowing attacker to intercept/modify all network traffic, install persistent malware, pivot to internal network, and disable security features.
Likely Case
Router takeover leading to DNS hijacking, credential theft, man-in-the-middle attacks, and botnet recruitment.
If Mitigated
Limited to denial of service if exploit fails or if network segmentation prevents access to vulnerable devices.
🎯 Exploit Status
Exploit code is publicly available. ZDI published technical details. Attack requires network adjacency but no authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware version 1.0.4.120 or later
Vendor Advisory: https://kb.netgear.com/000064313/Security-Advisory-for-Pre-Authentication-Buffer-Overflow-on-Some-Extenders-Routers-and-DSL-Modem-Routers-PSV-2021-0159
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to Advanced > Administration > Firmware Update. 3. Check for updates. 4. Download and install firmware version 1.0.4.120 or later. 5. Reboot router after update completes.
🔧 Temporary Workarounds
Disable remote administration
allPrevents external access to router's web interface
Network segmentation
allIsolate vulnerable routers on separate VLANs
🧯 If You Can't Patch
- Replace affected hardware with patched or different vendor equipment
- Implement strict network access controls to limit who can reach router management interfaces
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface under Advanced > Administration > Firmware UpdateCheck Version:
curl -s http://router-ip/currentsetting.htm | grep firmwareVerify Fix Applied:
Confirm firmware version is 1.0.4.120 or later in router admin interface📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests to router on port 80
- Multiple failed exploit attempts in httpd logs
- Router reboot events after suspicious activity
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains from router
- HTTP traffic patterns matching known exploit payloads
SIEM Query:
source="router_logs" AND (http_status=200 AND uri CONTAINS "strings" AND content_length>1000) OR (process="httpd" AND event="segmentation_fault")🔗 References
- https://kb.netgear.com/000064313/Security-Advisory-for-Pre-Authentication-Buffer-Overflow-on-Some-Extenders-Routers-and-DSL-Modem-Routers-PSV-2021-0159
- https://www.zerodayinitiative.com/advisories/ZDI-21-1274/
- https://kb.netgear.com/000064313/Security-Advisory-for-Pre-Authentication-Buffer-Overflow-on-Some-Extenders-Routers-and-DSL-Modem-Routers-PSV-2021-0159
- https://www.zerodayinitiative.com/advisories/ZDI-21-1274/
