CVE-2020-25367
📋 TL;DR
This CVE describes a command injection vulnerability in the HNAP1 protocol of D-Link DIR-823G routers. Attackers can execute arbitrary commands via shell metacharacters in the Captcha field during login, potentially gaining full control of affected devices. Only DIR-823G routers with specific firmware versions are affected.
💻 Affected Systems
- D-Link DIR-823G
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to install persistent malware, intercept network traffic, pivot to internal networks, or use device in botnets.
Likely Case
Remote code execution leading to device takeover, credential theft, or participation in DDoS attacks.
If Mitigated
Limited impact if device is behind firewall with restricted WAN access and strong network segmentation.
🎯 Exploit Status
Exploit requires no authentication and has public proof-of-concept code available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor for latest firmware
Vendor Advisory: https://www.dlink.com/en/security-bulletin/
Restart Required: Yes
Instructions:
1. Visit D-Link support site. 2. Download latest firmware for DIR-823G. 3. Log into router admin interface. 4. Navigate to Firmware Update section. 5. Upload and apply new firmware. 6. Reboot router.
🔧 Temporary Workarounds
Disable HNAP1 Protocol
allDisable the vulnerable HNAP1 protocol if not required
Restrict WAN Access
allBlock router admin interface from WAN/internet access
🧯 If You Can't Patch
- Isolate device on separate VLAN with strict firewall rules
- Implement network monitoring for suspicious login attempts and shell commands
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under System > FirmwareCheck Version:
Check via web interface or SSH if enabled: cat /proc/versionVerify Fix Applied:
Verify firmware version is newer than V1.0.2B05 and test Captcha field with metacharacters📡 Detection & Monitoring
Log Indicators:
- Unusual login attempts with shell metacharacters in Captcha field
- Unexpected command execution in system logs
Network Indicators:
- HTTP POST requests to /HNAP1/ with shell commands in parameters
- Unusual outbound connections from router
SIEM Query:
source="router_logs" AND ("Captcha" AND ("|" OR ";" OR "$" OR "`"))