CVE-2026-5842: Decolua 9router Auth Bypass Vulnerability

CVE-2026-5842 Overview

A security vulnerability has been identified in decolua 9router versions up to 0.3.47. The vulnerability exists in an unknown function of the /api endpoint within the Administrative API component. Improper authorization controls allow attackers to bypass security restrictions, potentially gaining unauthorized access to administrative functions. The vulnerability can be exploited remotely over the network without requiring authentication, and a public exploit has been disclosed.

Critical Impact

Unauthenticated attackers can bypass authorization controls on the Administrative API endpoint, potentially compromising router management functionality and network infrastructure.

Affected Products

• decolua 9router versions up to 0.3.47

Discovery Timeline

• April 9, 2026 - CVE-2026-5842 published to NVD
• April 9, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5842

Vulnerability Analysis

This authorization bypass vulnerability (CWE-285: Improper Authorization) affects the Administrative API Endpoint of decolua 9router. The vulnerability stems from inadequate access control mechanisms in the /api component, allowing remote attackers to perform actions that should be restricted to authenticated administrators.

The attack can be executed remotely over the network without requiring any prior authentication or user interaction. An attacker exploiting this vulnerability could potentially access or modify router configurations, view sensitive network information, or perform other administrative operations depending on the exposed API functionality.

Root Cause

The root cause is improper authorization (CWE-285) within the /api endpoint handler. The affected function fails to properly validate user permissions before processing administrative requests, allowing unauthorized access to protected resources and operations.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can send specially crafted HTTP requests to the /api endpoint to bypass authorization checks. Since no authentication is required and the vulnerability is remotely exploitable, any network-accessible instance of the affected router software is potentially at risk.

The vulnerability mechanism involves sending requests to the Administrative API Endpoint that bypass the expected authorization flow. Technical details and proof-of-concept information have been publicly disclosed through the GitHub Exploit Repository and documented in VulDB #356298.

Detection Methods for CVE-2026-5842

Indicators of Compromise

• Unexpected or unauthorized API requests to the /api endpoint from external IP addresses
• Administrative configuration changes without corresponding authenticated sessions
• Anomalous access patterns to router management interfaces during non-business hours
• Web server logs showing repeated requests to administrative API endpoints from unrecognized sources

Detection Strategies

• Monitor HTTP traffic to the /api endpoint for requests lacking proper authentication headers
• Implement network intrusion detection rules to identify exploitation attempts against the Administrative API
• Review access logs for successful API responses to unauthenticated requests
• Deploy web application firewall (WAF) rules to detect and block authorization bypass attempts

Monitoring Recommendations

• Enable verbose logging on the decolua 9router Administrative API component
• Configure alerts for any administrative actions performed without proper authentication
• Implement real-time monitoring of configuration changes on affected router instances
• Establish baseline network traffic patterns to identify anomalous API access attempts

How to Mitigate CVE-2026-5842

Immediate Actions Required

• Upgrade decolua 9router to version 0.3.75 or later immediately
• Restrict network access to the /api endpoint using firewall rules until patching is complete
• Audit existing router configurations for unauthorized changes
• Review access logs for evidence of exploitation attempts

Patch Information

The vendor has released version 0.3.75 which addresses this vulnerability. Upgrading to this version or later is the recommended remediation. The fixed release is available from the GitHub Release v0.3.75. Additional details about the vulnerability and fix are documented in GitHub Issue #431.

Workarounds

• Implement network-level access controls to restrict access to the Administrative API endpoint
• Use a reverse proxy with authentication in front of the /api endpoint
• Disable remote access to the Administrative API if not operationally required
• Deploy IP-based allowlisting to limit API access to trusted management networks only

# Example: Restrict access to /api endpoint using iptables
# Allow only trusted management subnet (adjust IP range as needed)
iptables -A INPUT -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP