CVE-2025-23041
📋 TL;DR
Umbraco.Forms has a vulnerability where character limits for form fields are only enforced client-side, not server-side. This allows attackers to bypass input validation by submitting data exceeding configured limits. All users of affected Umbraco.Forms versions are impacted.
💻 Affected Systems
- Umbraco.Forms
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could inject malicious payloads exceeding character limits, potentially leading to data corruption, injection attacks, or denial of service through resource exhaustion.
Likely Case
Attackers bypass form validation to submit oversized data, potentially causing application errors, data integrity issues, or enabling other injection vulnerabilities.
If Mitigated
With proper input validation and length checking server-side, the risk is limited to minor data validation bypasses.
🎯 Exploit Status
Exploitation requires only modifying HTTP requests to bypass client-side validation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.13.16, 10.5.7, 13.2.2, or 14.1.2 depending on your major version
Vendor Advisory: https://github.com/umbraco/Umbraco.Forms.Issues/security/advisories/GHSA-9v8m-qv22-f268
Restart Required: Yes
Instructions:
1. Identify your Umbraco.Forms version. 2. Upgrade to the patched version matching your major version (8.x, 10.x, 13.x, or 14.x). 3. Restart the application. 4. Test form submissions to verify server-side validation.
🧯 If You Can't Patch
- Implement server-side input validation middleware to check character limits before processing form submissions.
- Use web application firewalls (WAF) to detect and block oversized form submissions.
🔍 How to Verify
Check if Vulnerable:
Submit form data exceeding configured character limits via tools like curl or Burp Suite. If accepted without server-side rejection, the system is vulnerable.Check Version:
Check the Umbraco.Forms package version in your project's package manager (NuGet) or application configuration.Verify Fix Applied:
After patching, attempt to submit oversized form data. The server should reject it with appropriate validation errors.📡 Detection & Monitoring
Log Indicators:
- Unusually large form submissions
- Validation errors for input length exceeding configured limits
- HTTP 400/422 responses for oversized data
Network Indicators:
- HTTP POST requests with form data significantly exceeding typical lengths
- Repeated submission attempts with varying payload sizes
SIEM Query:
source="web_server" AND (request_size > 10000 OR form_field_length > [configured_limit])