CVE-2021-27891
📋 TL;DR
SSH Tectia Client and Server on Windows versions before 6.4.19 have weak key generation in ConnectSecure, potentially allowing attackers to compromise SSH sessions. This affects Windows installations of SSH Tectia products using ConnectSecure. The vulnerability could lead to unauthorized access to encrypted communications.
💻 Affected Systems
- SSH Tectia Client
- SSH Tectia Server
- ConnectSecure
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could decrypt SSH sessions, intercept sensitive data, perform man-in-the-middle attacks, and gain unauthorized access to systems protected by SSH Tectia.
Likely Case
Targeted attacks against organizations using vulnerable SSH Tectia deployments, potentially leading to credential theft and data exfiltration.
If Mitigated
With proper network segmentation and monitoring, impact would be limited to isolated systems with minimal lateral movement potential.
🎯 Exploit Status
Exploitation requires network access to SSH services and knowledge of weak key generation patterns.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 6.4.19 or later
Vendor Advisory: https://info.ssh.com/tectia-vulnerability-cve-2021-27891
Restart Required: Yes
Instructions:
1. Download SSH Tectia version 6.4.19 or later from SSH.com
2. Backup current configuration
3. Install the update following vendor instructions
4. Restart SSH Tectia services
5. Regenerate SSH keys if previously generated with vulnerable versions
🔧 Temporary Workarounds
Disable ConnectSecure
windowsTemporarily disable ConnectSecure component if not essential
Refer to SSH Tectia documentation for ConnectSecure disable procedures
Network Segmentation
allRestrict network access to SSH Tectia services
Use firewall rules to limit SSH access to trusted IPs only
🧯 If You Can't Patch
- Implement strict network access controls to limit exposure
- Monitor SSH sessions for unusual patterns and implement additional authentication layers
🔍 How to Verify
Check if Vulnerable:
Check SSH Tectia version in Windows Programs and Features or via 'tectia-version' commandCheck Version:
tectia-versionVerify Fix Applied:
Verify version is 6.4.19 or later and test SSH key generation📡 Detection & Monitoring
Log Indicators:
- Unusual SSH connection patterns
- Failed authentication attempts from unexpected sources
- SSH key generation events
Network Indicators:
- SSH traffic to/from non-standard ports
- Unencrypted SSH traffic patterns
SIEM Query:
source="ssh_tectia" AND (event_type="connection" OR event_type="authentication") | stats count by src_ip dest_ip