CVE-2026-2870
📋 TL;DR
A stack-based buffer overflow vulnerability in Tenda A21 routers allows remote attackers to execute arbitrary code by manipulating the QoS configuration. This affects Tenda A21 routers running firmware version 1.0.0.0. Attackers can exploit this without authentication to potentially take full control of affected devices.
💻 Affected Systems
- Tenda A21
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, enabling attackers to install malware, pivot to internal networks, or create persistent backdoors.
Likely Case
Remote code execution allowing attackers to modify router settings, intercept traffic, or use the device as part of a botnet.
If Mitigated
Limited impact if devices are behind firewalls with strict inbound filtering, though internal network exposure remains a risk.
🎯 Exploit Status
Public exploit code is available on GitHub, making exploitation trivial for attackers with basic skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.tenda.com.cn/
Restart Required: Yes
Instructions:
1. Check Tenda's official website for firmware updates. 2. Download the latest firmware for A21. 3. Log into router admin interface. 4. Navigate to System Tools > Firmware Upgrade. 5. Upload and install the new firmware. 6. Reboot the router.
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to the vulnerable interface by disabling remote administration features.
Network Segmentation
allIsolate affected routers in separate network segments with strict firewall rules.
🧯 If You Can't Patch
- Replace affected devices with patched or different vendor equipment
- Implement strict network access controls to limit exposure to the router's management interface
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via admin interface at System Status > Firmware Version. If version is 1.0.0.0, device is vulnerable.Check Version:
Check via web interface or attempt to access http://router-ip/goform/formSetQosBand (though this could trigger exploitation)Verify Fix Applied:
After updating firmware, verify the version has changed from 1.0.0.0 to a newer version.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /goform/formSetQosBand
- Router crash/reboot logs
- Unusual outbound connections from router
Network Indicators:
- HTTP POST requests to router IP on port 80/443 with abnormal payload sizes
- Traffic patterns suggesting router compromise
SIEM Query:
source="router_logs" AND (uri="/goform/formSetQosBand" OR message="buffer overflow" OR message="segmentation fault")