CVE-2020-26892
📋 TL;DR
This vulnerability in NATS nats-server allows attackers to bypass authentication by using expired JWT credentials, potentially gaining unauthorized access to the messaging system. It affects all deployments using JWT authentication with nats-server versions before 2.1.9.
💻 Affected Systems
- NATS nats-server
📦 What is this software?
Fedora by Fedoraproject
Nats Server by Linuxfoundation
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where attackers gain administrative access to the NATS messaging system, allowing them to intercept, modify, or inject messages across all connected applications.
Likely Case
Unauthorized access to the messaging system enabling attackers to eavesdrop on sensitive data, inject malicious messages, or disrupt message flow between applications.
If Mitigated
Limited impact with proper network segmentation and additional authentication layers, though expired credentials could still be misused within the NATS system.
🎯 Exploit Status
Exploitation requires obtaining expired JWT credentials, which could be gathered from logs, previous connections, or other sources.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.1.9 and later
Vendor Advisory: https://github.com/nats-io/nats-server/commits/master
Restart Required: Yes
Instructions:
1. Download nats-server version 2.1.9 or later from https://github.com/nats-io/nats-server/releases
2. Stop the current nats-server process
3. Replace the binary with the new version
4. Restart the nats-server service
🔧 Temporary Workarounds
Disable JWT Authentication
allTemporarily switch to alternative authentication methods or disable authentication if not required
Modify nats-server configuration to remove JWT authentication settings
Network Segmentation
allRestrict access to NATS server to trusted networks only
Configure firewall rules to limit inbound connections to NATS server
🧯 If You Can't Patch
- Implement network-level authentication and encryption (TLS/mTLS) for all NATS connections
- Deploy an API gateway or reverse proxy with additional authentication layers in front of NATS
🔍 How to Verify
Check if Vulnerable:
Check nats-server version with 'nats-server -v' and verify it's below 2.1.9, and confirm JWT authentication is enabled in configurationCheck Version:
nats-server -vVerify Fix Applied:
After patching, verify version is 2.1.9 or higher with 'nats-server -v' and test that expired JWT tokens are properly rejected📡 Detection & Monitoring
Log Indicators:
- Authentication attempts with expired JWT tokens
- Unexpected successful authentications
- Access from unusual IP addresses
Network Indicators:
- Unauthorized connections to NATS ports
- Suspicious message patterns or injection attempts
SIEM Query:
source="nats-server" AND ("authentication failed" OR "JWT expired") | stats count by src_ip🔗 References
- https://github.com/nats-io/nats-server/commits/master
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VT67XCLIIBYRT762SVFBYFFTQFVSM3SI/
- https://www.openwall.com/lists/oss-security/2020/11/02/2
- https://github.com/nats-io/nats-server/commits/master
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VT67XCLIIBYRT762SVFBYFFTQFVSM3SI/
- https://www.openwall.com/lists/oss-security/2020/11/02/2
