CVE-2021-3708
📋 TL;DR
CVE-2021-3708 is an OS command injection vulnerability in D-Link DSL-2750U routers with firmware vME1.16 or earlier. Unauthenticated attackers on the local network can execute arbitrary operating system commands on the device, potentially gaining full control. This vulnerability requires exploitation alongside CVE-2021-3707 for successful attack.
💻 Affected Systems
- D-Link DSL-2750U
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router allowing attacker to intercept all network traffic, install persistent malware, pivot to other devices on the network, or brick the device.
Likely Case
Attacker gains administrative access to router, modifies DNS settings, intercepts credentials, or uses router as pivot point for further attacks.
If Mitigated
Limited impact due to network segmentation, but still allows attacker to compromise the router itself.
🎯 Exploit Status
Exploit code is publicly available. Attack requires local network access and chaining with CVE-2021-3707.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware version newer than vME1.16
Vendor Advisory: https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10230
Restart Required: Yes
Instructions:
1. Download latest firmware from D-Link support site. 2. Log into router admin interface. 3. Navigate to Maintenance > Firmware Update. 4. Upload and install new firmware. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Network Segmentation
allIsolate router management interface to separate VLAN or restrict access to trusted devices only.
Access Control
allImplement MAC address filtering or firewall rules to restrict access to router management interface.
🧯 If You Can't Patch
- Replace affected router with newer model that receives security updates
- Place router behind dedicated firewall with strict access controls
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router web interface under Maintenance > Firmware Update. If version is vME1.16 or earlier, device is vulnerable.Check Version:
curl -s http://router-ip/status.html | grep -i firmwareVerify Fix Applied:
After firmware update, verify version shows newer than vME1.16 in router admin interface.📡 Detection & Monitoring
Log Indicators:
- Unusual command execution in router logs
- Multiple failed login attempts followed by successful access
- Unexpected firmware modification attempts
Network Indicators:
- Unusual outbound connections from router
- DNS queries to suspicious domains
- Unexpected port scans originating from router
SIEM Query:
source="router_logs" AND ("command injection" OR "unauthorized access" OR "firmware modified")🔗 References
- https://github.com/HadiMed/firmware-analysis/blob/main/DSL-2750U%20%28firmware%20version%201.6%29/README.md
- https://jvn.jp/en/vu/JVNVU92088210/
- https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10230
- https://github.com/HadiMed/firmware-analysis/blob/main/DSL-2750U%20%28firmware%20version%201.6%29/README.md
- https://jvn.jp/en/vu/JVNVU92088210/
- https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10230
