CVE-2024-40455

Executive Summary

CVE-2024-40455 is an arbitrary file deletion vulnerability discovered in ThinkSAAS v3.7, a popular open-source social networking and community management system. The flaw allows an unauthenticated or low-privileged attacker to delete arbitrary files on the server by sending a crafted HTTP request. This can lead to denial of service, data loss, or further exploitation by removing critical application files (e.g., configuration files, logs, or security controls). The vulnerability is classified under CWE-73 (External Control of File Name or Path), indicating improper sanitization of user-supplied input used in file operations. No official patch has been released, and the CVSS score is currently unassigned, but the impact is considered high due to the potential for complete file system compromise.

Supply Chain & Package Security

ThinkSAAS is a PHP-based application. The vulnerability resides in the core file handling logic, not in a third-party package. However, administrators should verify the integrity of their ThinkSAAS installation and monitor for any unauthorized modifications to core files.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, a reasonable assessment based on the vulnerability characteristics is:

• Attack Vector (AV): Network (N) – The attack can be launched remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the only affected component.
• Confidentiality (C): None (N) – File deletion does not directly leak data.
• Integrity (I): High (H) – Arbitrary file deletion can destroy critical data.
• Availability (A): High (H) – Deleting essential files can cause denial of service.

Estimated CVSS Score: 9.1 (Critical)

Threat Level: Critical – Exploitation is straightforward and can lead to complete system compromise or denial of service.

Deep Dive & Mechanics

The vulnerability exists in ThinkSAAS v3.7 due to insufficient validation of user-supplied file paths in file deletion operations. The application likely uses a function similar to unlink() or file_delete() that accepts a path parameter from user input without proper sanitization or path traversal checks.

Attack Flow:

1. The attacker identifies an endpoint that accepts a file path parameter (e.g., /index.php?app=file&act=delete&path=...).
2. The attacker crafts a request with a path traversal sequence (e.g., ../../config.php) to target files outside the intended directory.
3. The application processes the request and deletes the specified file without verifying that the path is within an allowed scope.
4. The attacker can delete multiple files sequentially, potentially removing critical application files, configuration files, or even system files if the web server has sufficient permissions.

Root Cause: The application fails to normalize the file path and does not restrict deletion to a specific directory (e.g., an uploads folder). This allows an attacker to use ../ sequences to traverse directories.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on common fixes.

Vulnerable Code (PHP):

<?php
$file = $_GET['path'];
if (file_exists($file)) {
    unlink($file);
    echo "File deleted.";
}
?>

Patched Code (PHP):

<?php
$allowed_dir = realpath(__DIR__ . '/uploads');
$file = realpath($_GET['path']);
if ($file !== false && strpos($file, $allowed_dir) === 0 && file_exists($file)) {
    unlink($file);
    echo "File deleted.";
} else {
    echo "Invalid file path.";
}
?>

The patched version uses realpath() to resolve the absolute path and then checks that the resolved path starts with the allowed directory. This prevents path traversal attacks.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A running instance of ThinkSAAS v3.7.
• Network access to the vulnerable endpoint.

Exploit Steps:

1. Identify the vulnerable endpoint (e.g., /index.php?app=file&act=delete).
2. Craft a request to delete a critical file, such as the configuration file:

   GET /index.php?app=file&act=delete&path=../../config.php HTTP/1.1
   Host: target.com
   

3. Verify deletion by attempting to access the file or observing application behavior.

Example using cURL:

curl -X GET "http://target.com/index.php?app=file&act=delete&path=../../config.php"

Impact: Deleting config.php can break the application, expose database credentials if the file is restored, or allow further attacks.

Blue Team (Detection & Prevention)

Detection:

• Monitor web server logs for requests containing ../ or ..\\ in file path parameters.
• Look for repeated requests to file deletion endpoints with varying paths.
• Use file integrity monitoring (FIM) to detect unexpected file deletions.

Prevention:

• Apply input validation and path normalization (as shown in the patched code).
• Restrict web server permissions to prevent deletion of critical files.
• Implement a Web Application Firewall (WAF) rule to block path traversal patterns.
• Upgrade to a patched version if available.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests containing ../ or ..\\ in parameters like path, file, or delete.
  • Repeated 200 OK responses to file deletion endpoints followed by application errors.
• File System IOCs:
  • Unexpected deletion of files such as config.php, .htaccess, index.php, or log files.
  • Presence of empty directories where files were removed.
• Log IOCs:
  • Web server access logs showing requests to /index.php?app=file&act=delete&path=../../.
  • Application error logs indicating missing files or failed includes.

Detection Engineering

YARA Rule

rule CVE_2024_40455_ThinkSAAS_File_Deletion {
    meta:
        description = "Detects attempts to exploit CVE-2024-40455 arbitrary file deletion in ThinkSAAS v3.7"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-40455"
    strings:
        $path_traversal = /(\.\.\/|\.\.\\){1,}/ nocase
        $delete_param = "act=delete" nocase
        $file_param = "path=" nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2024-40455 ThinkSAAS Arbitrary File Deletion Attempt
id: 8a3f2c1e-5b7d-4a9f-8c6e-2d1f3a4b5c6d
status: experimental
description: Detects HTTP requests attempting to exploit CVE-2024-40455 by using path traversal in file deletion parameters.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 
            - 'act=delete'
            - 'path='
        cs-uri-query|re: '(\.\.\/|\.\.\\){1,}'
    condition: selection
falsepositives:
    - Legitimate use of path traversal in other contexts (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-40455 ThinkSAAS Arbitrary File Deletion Attempt"; flow:to_server; content:"act=delete"; http_uri; content:"path="; http_uri; pcre:"/(\.\.\/|\.\.\\){1,}/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable file deletion functionality if not required, by removing or commenting out the vulnerable code.
2. Apply input validation – Sanitize and normalize file paths using realpath() and restrict deletion to a specific directory.
3. Restrict web server permissions – Ensure the web server user (e.g., www-data) has minimal write/delete permissions.
4. Monitor logs – Actively watch for path traversal attempts in web server logs.

Long-term Fix:

• Wait for an official patch from ThinkSAAS or apply the patched code example provided in this report.
• Consider migrating to a more actively maintained alternative if no patch is released.

Workaround:

• Use a Web Application Firewall (WAF) to block requests containing ../ in file path parameters.
• Implement a custom middleware that validates all file operations against a whitelist of allowed directories.

Valters IT
Securing Digital Frontiers