CVE-2020-29376
📋 TL;DR
This CVE exposes a hardcoded administrative password '!j@l#y$z%x6x7q8c9z)' for the TELNET service on affected V-SOL OLT devices. Attackers can use this password to gain full administrative access to the devices. Organizations using the specified V-SOL OLT models and firmware versions are vulnerable.
💻 Affected Systems
- V-SOL V1600D
- V1600D4L
- V1600D-MINI
- V1600G1
- V1600G2
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of OLT devices allowing attackers to reconfigure network infrastructure, intercept/modify traffic, disable services, or use devices as pivot points into internal networks.
Likely Case
Unauthorized administrative access leading to network disruption, configuration changes, and potential data interception.
If Mitigated
Limited impact if TELNET is disabled, network segmentation is implemented, and strong access controls are in place.
🎯 Exploit Status
Exploitation requires only TELNET access and knowledge of the hardcoded password. No authentication bypass or complex techniques needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: No
Instructions:
No official patch available. Contact V-SOL vendor for updated firmware or mitigation guidance.
🔧 Temporary Workarounds
Disable TELNET Service
allDisable the TELNET service on affected devices to prevent exploitation via this vector.
telnet disable
no telnet server enable
Implement Network Access Controls
allRestrict access to TELNET ports (typically TCP 23) using firewall rules or network segmentation.
iptables -A INPUT -p tcp --dport 23 -j DROP
access-list 101 deny tcp any any eq 23
🧯 If You Can't Patch
- Isolate affected devices in a separate VLAN with strict access controls
- Implement monitoring and alerting for TELNET authentication attempts
🔍 How to Verify
Check if Vulnerable:
Attempt TELNET connection to device port 23 and use password '!j@l#y$z%x6x7q8c9z)' for admin accountCheck Version:
show version or display version in device CLIVerify Fix Applied:
Verify TELNET service is disabled or inaccessible, and test that password no longer grants access📡 Detection & Monitoring
Log Indicators:
- Successful TELNET authentication with admin account
- Multiple failed TELNET login attempts followed by success
Network Indicators:
- TELNET connections to device port 23 from unexpected sources
- Traffic patterns indicating administrative configuration changes
SIEM Query:
source_port=23 AND (event_type="authentication_success" OR user="admin")