CVE-2025-67288

Executive Summary

CVE-2025-67288 describes a disputed arbitrary file upload vulnerability in Umbraco CMS v16.3.3. The claim is that an attacker can upload a crafted PDF file leading to arbitrary code execution. The vendor disputes this, stating that file validation is the responsibility of the system administrator implementing Umbraco CMS, not the CMS itself. This issue is related to CVE-2023-49279. No public proof-of-concept, exploit code, or patch details are currently available. The EPSS score is 0.0%, indicating no active exploitation in the wild.

Supply Chain & Package Security

Umbraco CMS is a .NET-based content management system. The vulnerability, if valid, would affect the core CMS package. No specific package version or patch is available from OSV or GitHub. Administrators should monitor the official Umbraco repository for updates.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or disputed status. No CVSS vector is provided. Given the disputed nature and lack of exploitation evidence, the threat level is currently Low. However, if the vulnerability is confirmed, it could be critical due to the potential for arbitrary code execution.

Deep Dive & Mechanics

The vulnerability is an arbitrary file upload (CWE-434) in Umbraco CMS v16.3.3. The attack vector involves uploading a crafted PDF file that, when processed, executes arbitrary code. The exact mechanism is unclear without a public PoC. The vendor's dispute suggests that the CMS does not enforce file validation by default, leaving it to the administrator to configure. This is a common point of contention in CMS security.

The related CVE-2023-49279 likely involves similar file upload issues. The lack of a patch or advisory from Umbraco indicates either the vulnerability is not accepted or a fix is in development.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable code is the file upload handler in Umbraco CMS v16.3.3. Without a patch, the comparison cannot be made. Administrators should review their file upload configurations and implement strict validation.

Exploitation & Lab Setup

Red Team

No public exploit code is available. To test, set up a local Umbraco v16.3.3 instance and attempt to upload a crafted PDF with embedded script (e.g., JavaScript in a PDF). Monitor server response and file execution.

# Example: Create a malicious PDF (requires tools like pdfkit)
# This is a placeholder - no actual exploit exists
echo "Creating test PDF..."
# Upload via HTTP POST to /umbraco/backoffice/UmbracoApi/Media/PostUpload
curl -X POST -F "file=@malicious.pdf" http://target/umbraco/backoffice/UmbracoApi/Media/PostUpload

Blue Team

Monitor file upload endpoints for unusual PDF files. Implement strict file validation on the server side, including MIME type checking, file signature verification, and scanning with antivirus. Disable execution of uploaded files in the web root.

# Example: Check for suspicious uploads in logs
grep "PostUpload" /var/log/umbraco/access.log | grep -i "pdf"

Indicators of Compromise (IOCs)

• File Hashes: None available.
• Network Indicators: Unusual POST requests to /umbraco/backoffice/UmbracoApi/Media/PostUpload with PDF files.
• File System: Unexpected PDF files in the upload directory with embedded scripts.
• Process: Unusual child processes spawned from the web server (e.g., cmd.exe, powershell).

Detection Engineering

YARA Rule

rule CVE_2025_67288_Umbraco_PDF_Upload
{
    meta:
        description = "Detects suspicious PDF files uploaded to Umbraco CMS"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-67288"
    strings:
        $pdf_header = { 25 50 44 46 }  // %PDF
        $js_embed = /\/JavaScript/i
        $embed_script = /\/EmbeddedFile/i
    condition:
        $pdf_header at 0 and ($js_embed or $embed_script)
}

Sigma Rule

title: Suspicious PDF Upload to Umbraco CMS
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects POST requests to Umbraco media upload endpoint with PDF files
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: iis
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/umbraco/backoffice/UmbracoApi/Media/PostUpload'
        cs-content-type: 'application/pdf'
    condition: selection
falsepositives:
    - Legitimate PDF uploads by administrators
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-67288 - Suspicious PDF Upload to Umbraco"; flow:to_server,established; http.method; content:"POST"; http.uri; content:"/umbraco/backoffice/UmbracoApi/Media/PostUpload"; http.content_type; content:"application/pdf"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Implement strict file upload validation on the server side. Only allow specific file types (e.g., images) and validate MIME types and file signatures.
2. Configuration: Follow Umbraco documentation to configure file upload restrictions. Disable execution of uploaded files in the web root.
3. Monitoring: Enable logging for all file uploads and monitor for suspicious activity.
4. Patch: Monitor the official Umbraco repository for any security updates related to this CVE.
5. Workaround: If possible, disable the media upload functionality or restrict it to authenticated administrators only.

Valters IT
Securing Digital Frontiers