CVE-2020-36970: PMB Path Traversal Vulnerability

CVE-2020-36970 Overview

PMB 5.6 contains a local file disclosure vulnerability in getgif.php that allows attackers to read arbitrary system files by manipulating the chemin parameter. This Path Traversal vulnerability (CWE-22) enables attackers to exploit unsanitized file path input to access sensitive files like /etc/passwd by sending crafted requests to the getgif.php endpoint.

Critical Impact

Unauthorized access to sensitive system files including configuration files, credentials, and other confidential data stored on the server hosting PMB 5.6.

Affected Products

• PMB 5.6

Discovery Timeline

• 2026-01-28 - CVE CVE-2020-36970 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2020-36970

Vulnerability Analysis

This vulnerability is classified as a Path Traversal (CWE-22) issue affecting the getgif.php endpoint in PMB 5.6. The vulnerability exists because the application fails to properly validate and sanitize the chemin parameter before using it in file system operations. An attacker with local access can manipulate this parameter to traverse directory structures and read files outside the intended directory scope.

The impact of successful exploitation is significant from a confidentiality perspective. Attackers can read arbitrary files from the server's file system, potentially exposing sensitive configuration files, database credentials, application source code, and system files such as /etc/passwd. This information disclosure can serve as a stepping stone for further attacks against the vulnerable system.

Root Cause

The root cause of CVE-2020-36970 is insufficient input validation on the chemin parameter within the getgif.php script. The application accepts user-controlled input and directly uses it to construct file paths without sanitizing directory traversal sequences such as ../. This allows attackers to escape the intended directory and access files anywhere on the file system that the web server process has read permissions for.

Attack Vector

The attack vector for this vulnerability requires local access to the system. An attacker can craft malicious requests to the getgif.php endpoint containing directory traversal sequences in the chemin parameter. By including path traversal characters like ../, the attacker can navigate out of the web application's root directory and access sensitive system files.

The vulnerability allows attackers to send specially crafted requests to getgif.php with manipulated chemin parameters containing directory traversal sequences. For example, an attacker could target paths like ../../../../etc/passwd to read system user information. Technical details and proof-of-concept information are available in the Exploit-DB #49054 entry and the VulnCheck PMB Local File Disclosure Advisory.

Detection Methods for CVE-2020-36970

Indicators of Compromise

• Unusual requests to getgif.php containing directory traversal sequences such as ../ or encoded variants like %2e%2e%2f
• Web server logs showing access attempts to getgif.php with suspicious chemin parameter values
• Access to sensitive system files like /etc/passwd, /etc/shadow, or application configuration files through the web application
• Unexpected file read operations by the web server process targeting system directories

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block path traversal patterns in the chemin parameter
• Monitor web server access logs for requests to getgif.php with path traversal sequences
• Deploy file integrity monitoring on critical system files to detect unauthorized access attempts
• Use intrusion detection systems configured with signatures for path traversal attacks

Monitoring Recommendations

• Enable detailed logging for all requests to getgif.php and similar endpoints
• Configure alerting for any access attempts containing ../ or URL-encoded traversal sequences
• Monitor for anomalous file system access patterns by the web server process
• Review web server logs regularly for suspicious activity targeting PMB endpoints

How to Mitigate CVE-2020-36970

Immediate Actions Required

• Upgrade PMB to a patched version that addresses the path traversal vulnerability in getgif.php
• Implement input validation to reject requests containing directory traversal sequences
• Restrict file system permissions for the web server process to limit the scope of potential file disclosure
• Deploy a web application firewall with rules to block path traversal attacks

Patch Information

Refer to the PMB File Project Repository for the latest updates and security patches. Additional information about PMB is available on the SIGB Main Website. Review the VulnCheck PMB Local File Disclosure Advisory for specific remediation guidance.

Workarounds

• Restrict access to getgif.php using web server access controls until a patch can be applied
• Implement a reverse proxy or WAF rule to filter requests containing path traversal sequences in the chemin parameter
• Use PHP's basename() or realpath() functions to sanitize file path inputs before file operations
• Consider disabling or removing the getgif.php script if its functionality is not required

# Example Apache configuration to restrict access to getgif.php
<Files "getgif.php">
    Order Deny,Allow
    Deny from all
    Allow from 127.0.0.1
</Files>