CVE-2020-36921: RED-V Super Digital Signage Disclosure

CVE-2020-36921 Overview

CVE-2020-36921 is an information disclosure vulnerability affecting the RED-V Super Digital Signage System version 5.1.1. This vulnerability allows unauthenticated attackers to access sensitive webserver log files by visiting multiple endpoints that expose system resources and debug log information without requiring any authentication.

Critical Impact

Unauthenticated attackers can retrieve sensitive log files and system resources, potentially exposing internal configuration details, user activity, and debug information that could facilitate further attacks against the signage system infrastructure.

Affected Products

• RED-V Super Digital Signage System 5.1.1

Discovery Timeline

• 2026-01-06 - CVE-2020-36921 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2020-36921

Vulnerability Analysis

This vulnerability falls under CWE-548 (Exposure of Information Through Directory Listing) and represents a significant information leakage risk in the RED-V Super Digital Signage System. The flaw exists in the web server component of the signage system, which fails to properly restrict access to sensitive endpoints that serve log files and system resources.

The vulnerability is exploitable over the network without any prior authentication or user interaction. An attacker can directly request specific endpoints to retrieve webserver logs and debug information, which may contain sensitive data such as internal IP addresses, system paths, user activity patterns, error messages revealing system configuration, and potentially credentials or session tokens logged during debugging operations.

Root Cause

The root cause of this vulnerability is the absence of proper access control mechanisms on endpoints that serve log files and system resources. The web application fails to implement authentication checks before allowing access to sensitive debugging and logging endpoints, exposing these resources to any network-accessible attacker.

Attack Vector

The attack vector is network-based, allowing remote unauthenticated attackers to exploit this vulnerability. The attack requires no user interaction and can be executed with low complexity by simply sending HTTP requests to the vulnerable endpoints.

The exploitation mechanism involves accessing specific URLs on the RED-V Super Digital Signage System web interface that serve log files without verifying the requester's authentication status. An attacker can enumerate and retrieve these files to gather intelligence about the target system.

For detailed technical analysis and proof-of-concept information, see the Zero Science Lab advisory ZSL-2020-5609 and the Packet Storm security disclosure.

Detection Methods for CVE-2020-36921

Indicators of Compromise

• Unusual HTTP requests to log file endpoints or debugging URLs on the RED-V system
• Multiple requests from single IP addresses attempting to access various system resource paths
• Web server access logs showing requests for sensitive file extensions (.log, .txt, .debug) from external sources
• Reconnaissance patterns indicating enumeration of web directories and files

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests to known sensitive log file paths
• Monitor HTTP access logs for requests targeting logging and debugging endpoints from unauthenticated sessions
• Deploy intrusion detection systems (IDS) with signatures for common information disclosure exploitation patterns
• Configure alerting for high volumes of 404/403 errors that may indicate endpoint enumeration attempts

Monitoring Recommendations

• Enable verbose logging on the RED-V signage system to track all access attempts to sensitive endpoints
• Implement network monitoring to identify unusual traffic patterns targeting the signage system web interface
• Establish baseline behavior for legitimate access patterns and alert on deviations
• Regularly audit web server access logs for evidence of attempted information disclosure attacks

How to Mitigate CVE-2020-36921

Immediate Actions Required

• Restrict network access to RED-V Super Digital Signage System web interfaces using firewall rules
• Implement authentication requirements for all sensitive endpoints including log files and debug resources
• Disable unnecessary debugging and logging endpoints in production environments
• Segment signage system networks from general corporate networks to limit attack surface

Patch Information

Organizations should consult the Red-V TV vendor website for official security updates and patch availability. Additional technical details and advisory information can be found in the VulnCheck Advisory, CxSecurity Issue WLB-2020110130, and IBM X-Force Vulnerability #191803.

Workarounds

• Deploy a reverse proxy with authentication in front of the RED-V web interface to enforce access controls
• Use network segmentation to isolate signage systems from untrusted network segments
• Implement IP whitelisting to restrict access to the web management interface to authorized administrator addresses only
• Configure web server to deny direct access to log directories and files through .htaccess or equivalent server configuration

# Example: Restrict access to log directories using iptables
# Allow only management network to access signage system web interface
iptables -A INPUT -p tcp --dport 80 -s 10.0.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 10.0.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP