CVE-2020-5849: Unraid Auth Bypass Vulnerability

CVE-2020-5849 Overview

CVE-2020-5849 is an authentication bypass vulnerability affecting Unraid 6.8.0. This vulnerability allows remote attackers to bypass authentication mechanisms on vulnerable Unraid NAS (Network Attached Storage) servers, potentially gaining unauthorized access to sensitive system resources and data without valid credentials.

Critical Impact

This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. With an EPSS score of 93.76%, this vulnerability has an extremely high probability of exploitation, placing it in the 99.8th percentile of all vulnerabilities.

Affected Products

• Unraid 6.8.0
• Unraid NAS servers running version 6.8.0

Discovery Timeline

• 2020-03-16 - CVE-2020-5849 published to NVD
• 2025-10-31 - Last updated in NVD database

Technical Details for CVE-2020-5849

Vulnerability Analysis

This authentication bypass vulnerability in Unraid 6.8.0 is classified under CWE-697 (Incorrect Comparison), indicating that the underlying flaw stems from improper comparison logic within the authentication mechanism. The vulnerability allows unauthenticated remote attackers to bypass security controls that should restrict access to the Unraid web management interface.

When exploited, attackers can gain unauthorized access to the Unraid server's administrative functions without providing valid credentials. This is particularly severe given that Unraid is commonly used as a home and small business NAS solution, often containing sensitive personal and business data. The vulnerability has been linked to CVE-2020-5847, which together form an exploit chain enabling unauthenticated remote code execution as root.

Root Cause

The root cause of this vulnerability lies in an incorrect comparison operation (CWE-697) within the authentication validation logic of Unraid 6.8.0. The flawed comparison logic fails to properly validate authentication credentials, allowing attackers to craft requests that bypass the authentication check entirely. This type of vulnerability often occurs when developers use improper comparison operators or when the authentication logic doesn't handle edge cases correctly.

Attack Vector

The attack vector for CVE-2020-5849 is network-based, requiring no user interaction or prior authentication. An attacker can remotely target any Unraid 6.8.0 server exposed to the network. The exploitation requires low attack complexity, making it accessible to attackers with minimal technical expertise.

The attack flow typically involves:

1. Identifying vulnerable Unraid 6.8.0 instances exposed to the network
2. Crafting malicious HTTP requests that exploit the incorrect comparison logic
3. Bypassing the authentication mechanism to gain unauthorized access
4. Once authenticated, the attacker may chain this with CVE-2020-5847 to achieve remote code execution as root

This vulnerability is particularly concerning because it can be combined with related vulnerabilities to achieve full system compromise with root privileges, as documented in the Sysdream security analysis.

Detection Methods for CVE-2020-5849

Indicators of Compromise

• Unexpected authentication events in Unraid server logs without corresponding valid login attempts
• Unauthorized changes to system configuration or user accounts
• Unusual network traffic patterns targeting the Unraid web management interface
• Evidence of command execution or file access without proper authentication records

Detection Strategies

• Monitor Unraid web server access logs for suspicious authentication bypass attempts
• Implement network-level monitoring for unusual traffic to Unraid management ports (typically port 80/443)
• Deploy intrusion detection rules to identify exploit patterns associated with this vulnerability
• Review system logs for signs of unauthorized administrative actions or root-level command execution

Monitoring Recommendations

• Configure alerting for failed and successful authentication attempts to Unraid management interfaces
• Implement file integrity monitoring on critical Unraid configuration files
• Monitor for new user account creation or privilege modifications
• Set up network segmentation alerts for any unexpected access to NAS management interfaces

How to Mitigate CVE-2020-5849

Immediate Actions Required

• Update Unraid to the latest available version immediately
• Restrict network access to the Unraid management interface using firewall rules
• Do not expose Unraid management interfaces directly to the internet
• Review access logs for signs of historical exploitation
• Consider placing Unraid servers behind a VPN for remote access

Patch Information

Unraid has addressed this vulnerability in versions released after 6.8.0. Users should check the Unraid Forum Announcements for the latest security updates and patch information. Given that this vulnerability is actively exploited and listed in CISA's KEV catalog, patching should be treated as the highest priority.

Workarounds

• Implement strict network segmentation to isolate Unraid servers from untrusted networks
• Use a reverse proxy with additional authentication layers in front of the Unraid management interface
• Disable remote access to the management interface if not required
• Monitor and log all access attempts to the Unraid web interface for forensic purposes

# Network isolation example using iptables
# Restrict Unraid management interface to trusted IP ranges only
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP