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How the CVE Works:
The vulnerability in Umbraco CMS (CVE-2025-XXXX) allows attackers to bypass configured file extension restrictions during uploads via a manipulated API request. The system fails to properly validate the file extension when processing uploads, enabling malicious actors to upload restricted file types (e.g., .aspx, .php) by altering the request metadata. This can lead to remote code execution (RCE) if the uploaded file is stored in an executable directory. The flaw stems from insufficient server-side validation, where the CMS checks only the client-provided `Content-Type` header instead of the actual file signature.
DailyCVE Form:
Platform: Umbraco CMS
Version: <15.4.2, <16.0.0
Vulnerability: File upload bypass
Severity: Critical
Date: Jun 5, 2025
Prediction: Patch expected Jun 10, 2025
What Undercode Say:
Analytics:
- Exploitability: High (low complexity, no auth required)
- Attack Vector: Network-based (API manipulation)
- Prevalence: Umbraco instances with public upload features.
Exploit Command (Proof-of-Concept):
curl -X POST "https://target.com/umbraco/api/upload" -H "Content-Type: image/jpeg" --data-binary "@malicious.aspx"
Detection (Check if vulnerable):
Invoke-WebRequest -Uri "https://target.com/umbraco/api/upload" -Method POST -Headers @{"Content-Type"="image/jpeg"} -Body "test"
Mitigation Steps:
- Immediate Patch: Upgrade to Umbraco 15.4.2 or 16.0.0.
- WAF Rule: Block mismatched `Content-Type` and file extensions.
3. Manual Fix (Pre-Patch):
// Custom validation in Umbraco API controller:
if (Path.GetExtension(file.FileName) != ".jpg") {
return BadRequest();
}
Log Monitoring:
SELECT FROM web_logs WHERE uri LIKE '%/umbraco/api/upload%' AND status_code = 200;
Post-Exploit Cleanup:
find /var/www/umbraco -name ".aspx" -mtime -1 -delete
References:
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
