CVE-2021-25309
📋 TL;DR
This vulnerability allows remote attackers to brute-force the administrative telnet service on Gigaset DX600A handsets due to no lockout/throttling and a weak 4-digit password policy. Attackers can gain full administrative access to the device. Only Gigaset DX600A devices with vulnerable firmware are affected.
💻 Affected Systems
- Gigaset DX600A Handset
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the device allowing attackers to install malware, intercept communications, pivot to internal networks, or use the device as a botnet node.
Likely Case
Unauthorized administrative access leading to device takeover, call interception, and potential lateral movement within the network.
If Mitigated
Limited to no impact if telnet service is disabled or strong access controls are implemented.
🎯 Exploit Status
Simple brute-force attack against telnet service with only 10,000 possible password combinations (0000-9999).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: No official vendor advisory found
Restart Required: No
Instructions:
No official patch available. Check Gigaset website for firmware updates or contact vendor support.
🔧 Temporary Workarounds
Disable Telnet Service
allDisable the telnet administrative service on port 650 if not required.
Access device admin interface > Disable telnet service
Network Access Control
linuxRestrict access to port 650 using firewall rules to only trusted IP addresses.
iptables -A INPUT -p tcp --dport 650 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 650 -j DROP
🧯 If You Can't Patch
- Isolate affected devices on separate VLAN with strict network segmentation
- Implement network monitoring for brute-force attempts on port 650
🔍 How to Verify
Check if Vulnerable:
Check if telnet service is running on port 650: nmap -p 650 <device_ip>Check Version:
Check device firmware version in admin interface or via telnet bannerVerify Fix Applied:
Verify telnet service is disabled or inaccessible: telnet <device_ip> 650 (should fail to connect)📡 Detection & Monitoring
Log Indicators:
- Multiple failed telnet authentication attempts from single source
- Successful telnet login from unexpected IP
Network Indicators:
- High volume of TCP connections to port 650
- Brute-force patterns in network traffic
SIEM Query:
source_port=650 AND (event_type="authentication_failed" OR event_type="authentication_successful") | stats count by src_ip🔗 References
- https://research.nccgroup.com/2021/02/28/technical-advisory-administrative-passcode-recovery-and-authenticated-remote-buffer-overflow-vulnerabilities-in-gigaset-dx600a-handset-cve-2021-25309-cve-2021-25306/
- https://research.nccgroup.com/2021/02/28/technical-advisory-administrative-passcode-recovery-and-authenticated-remote-buffer-overflow-vulnerabilities-in-gigaset-dx600a-handset-cve-2021-25309-cve-2021-25306/
