CVE-2025-59547

Executive Summary

CVE-2025-59547 is a path traversal vulnerability in the DNN (formerly DotNetNuke) content management system, affecting versions prior to 10.1.0. The vulnerability resides in the CKEditor file upload endpoint, where insufficient sanitization of filenames allows an attacker to probe internal network endpoints. By crafting a request with Unicode characters, an attacker can manipulate the file path to expose resources within the internal network of the hosted site. The CVSS score is 5.3 (Medium), and the EPSS score is 0.0%, indicating low exploitation likelihood. No public proof-of-concept or exploit code is available at this time.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a core vulnerability in the DNN CMS platform, which is built on the Microsoft .NET ecosystem. The CKEditor component is bundled with DNN, and the issue lies in how DNN handles file uploads through this editor.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: None
• Availability Impact: None

The vulnerability allows an unauthenticated attacker to probe internal network endpoints, potentially revealing sensitive information about the internal network architecture. The low confidentiality impact reflects the limited nature of the information disclosure, as the attacker can only probe endpoints, not directly access files.

Deep Dive & Mechanics

The vulnerability exists in the CKEditor file upload endpoint within DNN. When a file is uploaded, the filename is processed to determine the storage path. The issue is that the sanitization logic does not properly handle Unicode characters, which can be used to traverse directories or probe network paths.

For example, an attacker could upload a file with a name like ..%C0%AF..%C0%AFetc%C0%AFpasswd (using overlong UTF-8 encoding) to attempt to read files outside the intended upload directory. However, the primary impact is probing internal network endpoints, such as http://internal-server/, by crafting a filename that, when processed, results in a request to an internal resource.

The vulnerability is patched in DNN version 10.1.0, where the filename sanitization has been improved to properly handle Unicode characters and prevent path traversal.

Vulnerable vs. Patched Code

The vulnerable code likely resides in the file upload handler for CKEditor. The patched version (10.1.0) introduces stricter validation of filenames, including normalization of Unicode characters and rejection of paths containing traversal sequences.

Vulnerable Code (Conceptual):

// Vulnerable: Insufficient sanitization
string fileName = Request.Files[0].FileName;
string filePath = Path.Combine(uploadDirectory, fileName);
// No validation for path traversal or Unicode normalization

Patched Code (Conceptual):

// Patched: Proper sanitization
string fileName = Path.GetFileName(Request.Files[0].FileName);
fileName = fileName.Normalize(NormalizationForm.FormC);
if (fileName.Contains("..") || fileName.Contains("/") || fileName.Contains("\\"))
{
    throw new SecurityException("Invalid filename");
}
string filePath = Path.Combine(uploadDirectory, fileName);

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker would need to craft a request to the CKEditor file upload endpoint with a specially crafted filename containing Unicode characters. The following is a conceptual example using curl:

curl -X POST -F "upload=@test.txt;filename=..%C0%AF..%C0%AFinternal%00endpoint" http://target.com/ckeditor/upload

This request attempts to use overlong UTF-8 encoding to traverse directories and probe an internal endpoint. The attacker would then observe the response to determine if the internal resource is accessible.

Lab Setup:

1. Install DNN version 10.0.0 or earlier on a Windows server with IIS.
2. Ensure the CKEditor file upload endpoint is accessible.
3. Use a tool like Burp Suite or Postman to send crafted requests.
4. Monitor server logs and responses to identify successful probing.

Blue Team

To detect exploitation attempts, monitor for unusual file upload requests to the CKEditor endpoint. Look for filenames containing Unicode characters, especially overlong UTF-8 sequences or null bytes. Additionally, monitor outbound connections from the web server to internal IP addresses, as the vulnerability may cause the server to make requests to internal endpoints.

Detection Steps:

1. Enable logging for all file upload requests.
2. Analyze filenames for path traversal patterns (e.g., .., %2e%2e, %C0%AE).
3. Monitor for unexpected outbound connections from the web server.
4. Use the detection rules provided below.

Indicators of Compromise (IOCs)

• Network: Outbound connections from the web server to internal IP addresses (e.g., 10.x.x.x, 172.16.x.x, 192.168.x.x) that are not part of normal operations.
• File: Uploaded files with names containing Unicode characters, especially overlong UTF-8 sequences or null bytes.
• Logs: Web server logs showing requests to the CKEditor upload endpoint with suspicious filenames.
• System: Unusual file creation in directories outside the intended upload path.

Detection Engineering

YARA Rule

rule CVE_2025_59547_DNN_FileUpload
{
    meta:
        description = "Detects attempts to exploit CVE-2025-59547 in DNN CKEditor file upload"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-59547"
    strings:
        $unicode_traversal = /(?:%[cC][0-9a-fA-F]{2}%[89aAbB][0-9a-fA-F]{2})|(?:\\x[cC][0-9a-fA-F]{2}\\x[89aAbB][0-9a-fA-F]{2})/
        $path_traversal = /\.\.(?:\\|\/|%2f|%5c)/
        $null_byte = /%00/
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-59547 DNN CKEditor File Upload Path Traversal
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects suspicious file upload requests to DNN CKEditor endpoint with path traversal patterns
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: iis
detection:
    selection:
        cs-uri-query|contains:
            - 'ckeditor'
            - 'upload'
        cs-uri-query|re:
            - '\.\.(?:\\|\/|%2f|%5c)'
            - '%[cC][0-9a-fA-F]{2}%[89aAbB][0-9a-fA-F]{2}'
            - '%00'
    condition: selection
falsepositives:
    - Legitimate use of Unicode characters in filenames
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-59547 DNN CKEditor File Upload Path Traversal"; flow:to_server; content:"ckeditor"; http_uri; content:"upload"; http_uri; pcre:"/\.\.(?:\\|\/|%2f|%5c)/Ui"; pcre:"/%[cC][0-9a-fA-F]{2}%[89aAbB][0-9a-fA-F]{2}/Ui"; pcre:"/%00/Ui"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade DNN to version 10.1.0 or later.
2. If upgrade is not immediately possible, disable the CKEditor file upload endpoint or restrict access to authenticated users only.
3. Implement web application firewall (WAF) rules to block requests with path traversal patterns in filenames.

Long-term Measures:

1. Regularly update DNN and all plugins to the latest versions.
2. Conduct security audits of file upload functionality.
3. Implement input validation and sanitization for all user-supplied data, especially filenames.
4. Monitor for CVEs related to DNN and apply patches promptly.

Workaround:

• Modify the CKEditor configuration to disable file uploads or restrict allowed file types.
• Use a reverse proxy to filter out malicious requests before they reach the DNN server.

Valters IT
Securing Digital Frontiers