CVE-2021-26709
📋 TL;DR
CVE-2021-26709 is a critical stack-based buffer overflow vulnerability in D-Link DSL-320B-D1 routers that allows unauthenticated remote attackers to execute arbitrary code and take complete control of affected devices. This affects all EU_1.25 and earlier firmware versions. The vulnerability is particularly dangerous because it requires no authentication and affects devices that are no longer supported by the vendor.
💻 Affected Systems
- D-Link DSL-320B-D1
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise leading to persistent remote access, credential theft, network pivoting, and potential botnet recruitment.
Likely Case
Remote code execution allowing attackers to install malware, intercept network traffic, or use the device as a proxy for further attacks.
If Mitigated
No impact if devices are properly segmented, firewalled, or replaced with supported hardware.
🎯 Exploit Status
Public exploit code available on Packet Storm Security. Exploitation requires sending specially crafted HTTP requests to the login.xgi endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: None available
Vendor Advisory: https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10216
Restart Required: No
Instructions:
No official patch exists. D-Link has declared these devices end-of-life. The only secure solution is hardware replacement.
🔧 Temporary Workarounds
Network Segmentation and Isolation
allIsolate affected devices in separate VLANs with strict firewall rules preventing external access to web management interface.
Access Control Lists
allImplement ACLs to restrict access to device management interfaces to trusted IP addresses only.
🧯 If You Can't Patch
- Immediately replace affected devices with supported hardware
- Implement strict network segmentation and firewall rules to block all external access to device management interfaces
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or SSH. If version is EU_1.25 or earlier, device is vulnerable.Check Version:
Check web interface at http://[device-ip]/ or use nmap to identify device model and firmware.Verify Fix Applied:
No fix available to verify. Only verification is confirming device replacement.📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts to login.xgi
- Unusual HTTP POST requests to login.xgi with long parameters
- Device reboot or configuration changes without authorization
Network Indicators:
- HTTP requests to /login.xgi with unusually long user/pass parameters
- Traffic from device to unexpected external IPs
- Port scanning originating from device
SIEM Query:
source="router_logs" AND (uri="/login.xgi" AND (param_length>100 OR status_code=500))🔗 References
- http://packetstormsecurity.com/files/162133/D-Link-DSL-320B-D1-Pre-Authentication-Buffer-Overflow.html
- http://seclists.org/fulldisclosure/2021/Apr/15
- https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10216
- https://www.dlink.com/en/security-bulletin
- http://packetstormsecurity.com/files/162133/D-Link-DSL-320B-D1-Pre-Authentication-Buffer-Overflow.html
- http://seclists.org/fulldisclosure/2021/Apr/15
- https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10216
- https://www.dlink.com/en/security-bulletin
