CVE-2026-3839: Unraid Auth Bypass Vulnerability

CVE-2026-3839 Overview

CVE-2026-3839 is a path traversal authentication bypass vulnerability affecting Unraid installations. This vulnerability allows remote attackers to bypass authentication on affected installations of Unraid without requiring any prior authentication. The flaw exists within the auth-request.php file, where improper validation of user-supplied paths enables attackers to circumvent authentication mechanisms entirely.

Critical Impact

Remote attackers can bypass authentication on Unraid systems without any credentials, potentially gaining unauthorized access to sensitive data and system controls.

Affected Products

• Unraid version 7.2.3
• Unraid (all versions prior to patched release)

Discovery Timeline

• 2026-03-16 - CVE-2026-3839 published to NVD
• 2026-03-17 - Last updated in NVD database

Technical Details for CVE-2026-3839

Vulnerability Analysis

This vulnerability is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), commonly known as Path Traversal. The flaw resides in the auth-request.php file within Unraid's authentication subsystem. The issue stems from insufficient validation of user-supplied path data before it is utilized in the authentication process.

When a user submits an authentication request, the affected component fails to properly sanitize path inputs, allowing an attacker to craft malicious requests that traverse the expected directory structure. This path traversal vulnerability directly impacts the authentication decision logic, enabling complete authentication bypass.

The network-accessible nature of this vulnerability means that any attacker with network access to an Unraid system can attempt exploitation without requiring any existing credentials or user interaction. This was reported to the Zero Day Initiative as ZDI-CAN-28912.

Root Cause

The root cause of CVE-2026-3839 is the lack of proper input validation within the auth-request.php file. The authentication mechanism accepts user-supplied path data and uses it in authentication decisions without adequately verifying that the path remains within expected boundaries. This allows attackers to supply specially crafted path traversal sequences that manipulate the authentication flow.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no authentication or user interaction. An attacker can send specially crafted HTTP requests to the Unraid web interface targeting the auth-request.php endpoint. By including path traversal sequences (such as ../) in the request, the attacker can manipulate the authentication logic to bypass credential verification.

The vulnerability can be exploited remotely over the network, making any internet-exposed or network-accessible Unraid installation a potential target. Successful exploitation grants the attacker access to the system as if they had provided valid credentials.

For detailed technical information about the exploitation mechanism, refer to the Zero Day Initiative Advisory ZDI-26-172.

Detection Methods for CVE-2026-3839

Indicators of Compromise

• HTTP requests to auth-request.php containing path traversal sequences such as ../, ..%2f, or encoded variants
• Unusual authentication success events from unknown or external IP addresses without corresponding valid login attempts
• Web server access logs showing repeated requests to authentication endpoints with malformed or suspicious path parameters

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block path traversal patterns in requests to authentication endpoints
• Monitor authentication logs for successful authentications that lack corresponding valid credential submissions
• Deploy intrusion detection system (IDS) signatures to identify path traversal attempts targeting auth-request.php

Monitoring Recommendations

• Enable detailed logging on the Unraid web server to capture full request URIs and parameters
• Set up alerts for authentication events originating from unexpected geographic locations or IP ranges
• Regularly audit access logs for patterns indicative of authentication bypass attempts

How to Mitigate CVE-2026-3839

Immediate Actions Required

• Restrict network access to Unraid systems by placing them behind a VPN or firewall that limits access to trusted IP addresses only
• Disable external/internet access to the Unraid web interface until a patch is applied
• Review authentication and access logs to identify any potential unauthorized access that may have occurred

Patch Information

Users should monitor Unraid's official channels and the Zero Day Initiative Advisory ZDI-26-172 for patch availability and update instructions. Apply vendor-provided security updates as soon as they become available.

Workarounds

• Implement network segmentation to isolate Unraid systems from untrusted networks
• Configure a reverse proxy with input validation rules to filter malicious path traversal attempts before they reach the Unraid application
• Use VPN-only access for remote administration of Unraid systems until a permanent fix is deployed

# Example: Restrict access to Unraid web interface via iptables
# Allow only trusted IP addresses to access the web interface

# Replace 192.168.1.0/24 with your trusted network range
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