CVE-2021-35943
📋 TL;DR
CVE-2021-35943 allows externally managed users in Couchbase Server to authenticate with empty passwords, violating RFC4513 authentication requirements. This affects Couchbase Server versions 6.5.x and 6.6.x through 6.6.2. Attackers can gain unauthorized access to database systems configured with external authentication.
💻 Affected Systems
- Couchbase Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of Couchbase Server with administrative access, leading to data theft, data destruction, or ransomware deployment across the database cluster.
Likely Case
Unauthorized access to sensitive data stored in Couchbase databases, potentially leading to data exfiltration or privilege escalation within the system.
If Mitigated
Limited impact if proper network segmentation and authentication controls prevent external access, though internal threats remain possible.
🎯 Exploit Status
Exploitation requires knowledge of externally managed usernames but no password. Attackers can attempt common usernames or enumerate users through other means.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 6.6.3 and later, 7.0.0 and later
Vendor Advisory: https://www.couchbase.com/alerts
Restart Required: Yes
Instructions:
1. Backup Couchbase Server configuration and data. 2. Download and install Couchbase Server 6.6.3 or later from official channels. 3. Follow Couchbase upgrade documentation for your deployment type. 4. Restart Couchbase services after installation.
🔧 Temporary Workarounds
Disable External Authentication
allTemporarily switch to internal Couchbase user management until patching is possible
# Configure Couchbase to use internal authentication only
# Refer to Couchbase documentation for specific configuration steps
Network Access Controls
linuxRestrict access to Couchbase authentication endpoints using firewall rules
# Example: Restrict port 8091 (web console) and LDAP ports
iptables -A INPUT -p tcp --dport 8091 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 8091 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Couchbase servers from untrusted networks
- Enable comprehensive logging and monitoring of authentication attempts to detect exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check Couchbase Server version and verify if external authentication is configured. Versions 6.5.x or 6.6.x through 6.6.2 with external auth are vulnerable.Check Version:
couchbase-server --version # or check web console at http://localhost:8091Verify Fix Applied:
After patching, verify version is 6.6.3+ or 7.0.0+. Test authentication with empty passwords for externally managed users should be rejected.📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts with empty passwords
- Successful logins from unexpected sources
- Multiple authentication attempts for the same user
Network Indicators:
- Unusual authentication traffic to Couchbase ports
- Connection attempts from unexpected IP ranges
SIEM Query:
source="couchbase" AND (event_type="authentication" OR event_type="login") AND (password="" OR password_length=0)