CVE-2026-2873
📋 TL;DR
A stack-based buffer overflow vulnerability in Tenda A21 routers allows remote attackers to execute arbitrary code by manipulating time parameters in the setSchedWifi function. 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, lateral movement to internal networks, persistent backdoor installation, and botnet recruitment.
Likely Case
Router compromise allowing traffic interception, DNS hijacking, credential theft, and denial of service to connected devices.
If Mitigated
Limited impact with proper network segmentation, though vulnerable devices remain at risk of compromise.
🎯 Exploit Status
Public exploit available on GitHub. Attack requires sending crafted HTTP POST request to /goform/openSchedWifi endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.tenda.com.cn/
Restart Required: Yes
Instructions:
1. Check Tenda website for firmware updates. 2. Download latest firmware. 3. Access router admin panel. 4. Navigate to firmware upgrade section. 5. Upload and apply new firmware. 6. Reboot router.
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to router web interface
Access router admin panel -> System -> Remote Management -> Disable
Network Segmentation
linuxIsolate router management interface from untrusted networks
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP
🧯 If You Can't Patch
- Replace affected router with patched or different model
- Implement strict firewall rules blocking all external access to router management interface
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin panel. If version is 1.0.0.0, device is vulnerable.Check Version:
curl -s http://router-ip/goform/getStatus | grep versionVerify Fix Applied:
Verify firmware version has changed from 1.0.0.0 to a newer version after update.📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /goform/openSchedWifi with abnormal time parameters
- Multiple failed buffer overflow attempts in system logs
Network Indicators:
- Unusual HTTP traffic to router management port (80/443) from external IPs
- POST requests with long schedStartTime/schedEndTime parameters
SIEM Query:
source="router.log" AND (uri="/goform/openSchedWifi" AND (schedStartTime.length>50 OR schedEndTime.length>50))