CVE-2021-46321
📋 TL;DR
This vulnerability is a stack buffer overflow in Tenda AC Series Router AC11 firmware's wifiBasicCfg module. Attackers can send specially crafted overflow data to cause a Denial of Service (DoS), potentially crashing the router. Users of affected Tenda AC11 routers with vulnerable firmware are impacted.
💻 Affected Systems
- Tenda AC Series Router AC11
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router crash requiring physical reset, potential remote code execution if exploit chains with other vulnerabilities, and persistent network disruption.
Likely Case
Router becomes unresponsive requiring reboot, disrupting all network connectivity for connected devices until manually restarted.
If Mitigated
If properly segmented and firewalled, impact limited to isolated network segment with quick recovery via reboot.
🎯 Exploit Status
Public proof-of-concept available in GitHub repository; exploitation requires sending crafted data to vulnerable endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: Yes
Instructions:
1. Check Tenda official website for firmware updates. 2. If update available, download and install via router admin interface. 3. Reboot router after update.
🔧 Temporary Workarounds
Disable remote management
allPrevent external access to router administration interface
Login to router admin > Advanced Settings > Remote Management > Disable
Network segmentation
allIsolate router management interface to trusted network segment only
🧯 If You Can't Patch
- Replace router with different model/brand that receives security updates
- Implement strict firewall rules blocking all external access to router management interfaces
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface: System Status > Firmware VersionCheck Version:
Login to router admin interface and navigate to System StatusVerify Fix Applied:
Verify firmware version is different from AC11_V02.03.01.104_CN📡 Detection & Monitoring
Log Indicators:
- Router crash/reboot logs
- Unusual traffic patterns to wifiBasicCfg endpoint
- Multiple failed connection attempts
Network Indicators:
- Unusual traffic to router management port (typically 80/443)
- Large payloads sent to router management interface
SIEM Query:
source="router.log" AND ("crash" OR "reboot" OR "wifiBasicCfg")