CVE-2020-9277
📋 TL;DR
This vulnerability allows attackers to bypass authentication on D-Link DSL-2640B routers and perform administrative tasks without credentials. Attackers can modify admin passwords, change router settings, or potentially gain full control of affected devices. This affects D-Link DSL-2640B B2 EU_4.01B devices.
💻 Affected Systems
- D-Link DSL-2640B
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router compromise allowing attacker to change all settings, intercept network traffic, install malware, and use the router as an attack platform.
Likely Case
Unauthorized administrative access leading to password changes, network configuration modifications, and potential credential theft.
If Mitigated
Limited impact if device is not internet-facing and network segmentation prevents lateral movement.
🎯 Exploit Status
Exploitation involves sending crafted HTTP requests to CGI modules without authentication. Public advisories include technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check D-Link for latest firmware updates
Vendor Advisory: https://www.dlink.com/en/security-bulletin
Restart Required: Yes
Instructions:
1. Visit D-Link support site. 2. Download latest firmware for DSL-2640B. 3. Log into router admin panel. 4. Navigate to firmware update section. 5. Upload and apply new firmware. 6. Reboot router.
🔧 Temporary Workarounds
Disable remote management
allPrevents external attackers from accessing router admin interface
Network segmentation
allIsolate router management interface to separate VLAN
🧯 If You Can't Patch
- Replace affected device with supported model
- Implement strict firewall rules blocking all external access to router management interface
🔍 How to Verify
Check if Vulnerable:
Attempt to access CGI modules without authentication. Check if administrative actions can be performed without login.Check Version:
Check router web interface or use command: telnet [router_ip] and check bannerVerify Fix Applied:
Verify authentication is required for all CGI module access after firmware update.📡 Detection & Monitoring
Log Indicators:
- Unauthenticated access to CGI modules
- Admin password change without login
- Multiple failed login attempts followed by successful CGI access
Network Indicators:
- HTTP requests to /cgi/* without authentication headers
- Unusual administrative actions from non-admin IPs
SIEM Query:
source="router_logs" AND (uri="/cgi/*" AND NOT auth_success="true")🔗 References
- https://raelize.com/advisories/CVE-2020-9277_D-Link-DSL-2640B_CGI-Authentication-bypass_v1.0.txt
- https://raelize.com/posts/d-link-dsl-2640b-security-advisories/
- https://www.dlink.com/en/security-bulletin
- https://raelize.com/advisories/CVE-2020-9277_D-Link-DSL-2640B_CGI-Authentication-bypass_v1.0.txt
- https://raelize.com/posts/d-link-dsl-2640b-security-advisories/
- https://www.dlink.com/en/security-bulletin
