CVE-2021-45043: HD-Network Monitoring Path Traversal Flaw

CVE-2021-45043 Overview

HD-Network Real-time Monitoring System 2.0 contains a critical directory traversal vulnerability that allows unauthenticated attackers to read arbitrary files from the underlying system. The vulnerability exists in the /language/lang endpoint where the s_Language parameter is improperly validated, allowing attackers to use ../ sequences to escape the intended directory and access sensitive system files including /etc/shadow.

Critical Impact

Unauthenticated attackers can read sensitive system files including password hashes from /etc/shadow, potentially leading to full system compromise through offline password cracking attacks.

Affected Products

• HD-Network Real-time Monitoring System 2.0
• hd-network_real-time_monitoring_system_project hd-network_real-time_monitoring_system

Discovery Timeline

• 2021-12-15 - CVE-2021-45043 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-45043

Vulnerability Analysis

This directory traversal vulnerability (CWE-22) allows remote attackers to read arbitrary files on the server without authentication. The root cause lies in insufficient input validation of the s_Language parameter within the /language/lang endpoint. When processing language file requests, the application fails to properly sanitize path traversal sequences, enabling attackers to navigate outside the intended web directory structure.

The vulnerability is particularly severe because it can be exploited remotely over the network without requiring any user interaction or authentication. Successful exploitation results in unauthorized disclosure of highly sensitive information, including system configuration files and password hashes.

Root Cause

The application does not properly sanitize the s_Language parameter before using it in file system operations. When a user requests a language file through the /language/lang endpoint, the application directly concatenates the user-supplied parameter to construct a file path without removing or blocking directory traversal sequences such as ../. This allows an attacker to traverse up the directory tree and access files outside the intended language directory, including sensitive system files like /etc/shadow.

Attack Vector

The attack is conducted remotely over the network by sending a crafted HTTP request to the vulnerable /language/lang endpoint. An attacker manipulates the s_Language parameter to include multiple ../ sequences, allowing navigation to the root filesystem and subsequent access to any readable file.

The attack flow proceeds as follows: the attacker identifies a vulnerable HD-Network Real-time Monitoring System instance, crafts a malicious request with directory traversal sequences in the s_Language parameter (such as ../../../../etc/shadow), sends the request to the target system, and receives the contents of the targeted file in the HTTP response. No authentication is required, making this vulnerability easily exploitable by any network-accessible attacker.

Detection Methods for CVE-2021-45043

Indicators of Compromise

• HTTP requests to /language/lang containing ../ sequences in the s_Language parameter
• Unusual access patterns to the /language/lang endpoint from external IP addresses
• Log entries showing attempts to access sensitive files like /etc/shadow, /etc/passwd, or configuration files
• Multiple rapid requests to the language endpoint from the same source with varying traversal depths

Detection Strategies

• Configure web application firewalls (WAF) to detect and block requests containing path traversal patterns (../, ..%2f, %2e%2e/)
• Implement intrusion detection system (IDS) rules to alert on directory traversal attempts in HTTP parameters
• Monitor web server access logs for requests to /language/lang with suspicious parameter values
• Deploy file integrity monitoring on sensitive system files to detect unauthorized access attempts

Monitoring Recommendations

• Enable detailed logging for all requests to the /language/lang endpoint
• Set up real-time alerts for any request containing directory traversal sequences
• Monitor for unusual file read operations on sensitive system files such as /etc/shadow and /etc/passwd
• Implement network traffic analysis to identify exploitation attempts from external sources

How to Mitigate CVE-2021-45043

Immediate Actions Required

• Restrict network access to HD-Network Real-time Monitoring System to trusted IP addresses only
• Implement a web application firewall rule to block requests containing ../ sequences
• Consider taking the vulnerable system offline until a patch is available or alternative mitigations are in place
• Audit system access logs for evidence of prior exploitation attempts

Patch Information

No vendor patch information is currently available in public advisories. Administrators should contact the HD-Network Real-time Monitoring System vendor directly for security updates. Additional technical details about this vulnerability can be found in the technical documentation on Google Drive.

Workarounds

• Implement strict input validation on the s_Language parameter to reject any input containing ../ or URL-encoded variants
• Use a web application firewall to filter malicious requests before they reach the application
• Restrict filesystem permissions so the web application process cannot read sensitive files like /etc/shadow
• Isolate the monitoring system on a segmented network with restricted access from untrusted networks
• Consider implementing a reverse proxy with path normalization to strip traversal sequences

# Example WAF rule to block directory traversal attempts (ModSecurity)
SecRule ARGS:s_Language "@contains ../" "id:1001,phase:1,deny,status:403,msg:'Directory Traversal Attempt Blocked'"
SecRule ARGS:s_Language "@rx \.\.(%2f|%5c|\/|\\)" "id:1002,phase:1,deny,status:403,msg:'Encoded Directory Traversal Blocked'"