CVE-2021-27248
📋 TL;DR
This is a critical buffer overflow vulnerability in D-Link DAP-2020 access points that allows network-adjacent attackers to execute arbitrary code as root without authentication. The flaw exists in CGI script processing where user-supplied data length isn't properly validated before copying to a fixed buffer. All installations of DAP-2020 v1.01rc001 are affected.
💻 Affected Systems
- D-Link DAP-2020
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise with root-level code execution, allowing attacker to install persistent backdoors, intercept network traffic, pivot to other network devices, or render the device unusable.
Likely Case
Remote code execution leading to device takeover, network traffic monitoring, and potential lateral movement within the network.
If Mitigated
Limited impact if device is isolated from untrusted networks and proper network segmentation is in place.
🎯 Exploit Status
ZDI published detailed advisory with exploitation details. The vulnerability requires network adjacency but no authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Later firmware versions (check vendor advisory)
Vendor Advisory: https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10201
Restart Required: Yes
Instructions:
1. Download latest firmware from D-Link support site. 2. Log into device web interface. 3. Navigate to System > Firmware Update. 4. Upload and apply new firmware. 5. Device will reboot automatically.
🔧 Temporary Workarounds
Network Segmentation
allIsolate DAP-2020 devices on separate VLANs or network segments to limit attack surface
Access Control Lists
allImplement firewall rules to restrict access to device management interface
🧯 If You Can't Patch
- Replace affected devices with patched models or different vendor products
- Deploy network-based intrusion prevention systems (IPS) with rules to detect and block exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface: System > Status > Firmware Version. If version is v1.01rc001, device is vulnerable.Check Version:
curl -s http://device-ip/status.cgi | grep firmwareVerify Fix Applied:
After firmware update, verify version is no longer v1.01rc001. Test web interface functionality remains intact.📡 Detection & Monitoring
Log Indicators:
- Unusual CGI script requests with long parameters
- Multiple failed buffer overflow attempts
- Unexpected device reboots
Network Indicators:
- HTTP requests to CGI endpoints with unusually long getpage parameters
- Traffic patterns indicating buffer overflow exploitation
SIEM Query:
source="dlink-access-point" AND (uri="*.cgi" AND uri_length>1000) OR (http_user_agent CONTAINS "exploit" OR "metasploit")