CVE-2026-24687: Umbraco Forms Path Traversal Vulnerability

CVE-2026-24687 Overview

CVE-2026-24687 is a Path Traversal vulnerability affecting Umbraco Forms, a form builder that integrates with the Umbraco content management system. The vulnerability allows authenticated backoffice users to enumerate and traverse paths on the system's filesystem and read their contents on Mac/Linux Umbraco installations. This issue specifically impacts the export functionality and can lead to unauthorized disclosure of sensitive system files.

Critical Impact

Authenticated attackers can read arbitrary files from the server filesystem, potentially exposing configuration files, credentials, source code, and other sensitive data on Mac/Linux deployments.

Affected Products

• Umbraco Forms version 16 (prior to 16.4.1)
• Umbraco Forms version 17 (prior to 17.1.1)
• Mac/Linux Umbraco installations (Windows/Umbraco Cloud not affected)

Discovery Timeline

• 2026-01-29 - CVE CVE-2026-24687 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-24687

Vulnerability Analysis

This vulnerability is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), commonly known as Path Traversal or Directory Traversal. The flaw exists within the export endpoint of Umbraco Forms at /umbraco/forms/api/v1/export.

The vulnerability requires authentication to the Umbraco backoffice, meaning an attacker must have valid credentials to exploit this issue. However, once authenticated, even low-privileged backoffice users can leverage the flaw to escape the intended directory constraints and access files anywhere on the server filesystem.

The attack surface is limited to Mac and Linux environments because the path traversal sequences that enable exploitation (such as ../) behave differently on Windows systems. Umbraco Cloud users are not impacted as the platform runs exclusively in Windows environments.

Root Cause

The root cause of this vulnerability is insufficient validation of the fileName parameter in the export API endpoint. The application fails to properly sanitize user-supplied input, allowing path traversal sequences like ../ or ..\\ to be processed and interpreted by the filesystem. This enables attackers to break out of the intended export directory and traverse to arbitrary locations on the server.

Attack Vector

The attack is executed over the network by an authenticated backoffice user sending malicious requests to the export endpoint. The attacker crafts requests containing path traversal sequences in the fileName parameter to navigate the filesystem hierarchy. For example, by including multiple ../ sequences, an attacker can traverse upward from the application's working directory to access sensitive files such as /etc/passwd, application configuration files, or database connection strings.

The exploitation flow involves:

1. Authenticating to the Umbraco backoffice with valid credentials
2. Sending a crafted request to /umbraco/forms/api/v1/export with path traversal sequences in the fileName parameter
3. The server processes the malicious filename without proper sanitization
4. The attacker receives the contents of the targeted file in the response

For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-24687

Indicators of Compromise

• HTTP requests to /umbraco/forms/api/v1/export containing path traversal patterns (../, ..\\, or URL-encoded variants)
• Unusual file access patterns in application logs showing requests for files outside the expected export directory
• Web server logs showing export requests with suspicious fileName parameter values

Detection Strategies

• Implement web application firewall (WAF) rules to detect and alert on path traversal sequences in request parameters
• Monitor access logs for requests to the export endpoint containing ../, ..%2f, or similar encoded path traversal patterns
• Configure intrusion detection systems (IDS) to flag requests targeting sensitive system files like /etc/passwd or configuration files
• Review Umbraco backoffice audit logs for suspicious export activity from user accounts

Monitoring Recommendations

• Enable detailed logging for the Umbraco Forms export endpoint and monitor for anomalous request patterns
• Set up alerts for any backoffice user attempting to access the export functionality with unusual frequency
• Monitor for failed file access attempts that may indicate probing behavior
• Implement file integrity monitoring on critical configuration files to detect unauthorized reads

How to Mitigate CVE-2026-24687

Immediate Actions Required

• Upgrade Umbraco Forms to the patched versions: 16.4.1 or 17.1.1 immediately
• Audit backoffice user accounts and remove unnecessary access privileges
• Review recent export endpoint access logs for signs of exploitation
• Verify that your deployment environment is running on Windows/Umbraco Cloud (which is not affected) or implement workarounds if on Mac/Linux

Patch Information

The vulnerability has been addressed in Umbraco Forms versions 16.4.1 and 17.1.1. Upgrading to these versions is strongly recommended as the primary remediation approach. The patches implement proper input validation on the fileName parameter to prevent path traversal attacks.

For additional details on the security fix, see the GitHub Security Advisory.

Workarounds

• Configure a WAF or reverse proxy to block requests containing path traversal sequences (../, ..\\) in the fileName parameter of the export endpoint
• Restrict network access to the Umbraco backoffice to trusted IP ranges only
• Block the /umbraco/forms/api/v1/export endpoint entirely if the export feature is not required for your use case
• Implement additional authentication controls or IP whitelisting for administrative functions

# Example nginx WAF-style configuration to block path traversal attempts
location /umbraco/forms/api/v1/export {
    # Block requests with path traversal patterns
    if ($query_string ~* "(\.\.\/|\.\.\\)") {
        return 403;
    }
    
    # Restrict access to trusted IP ranges
    allow 10.0.0.0/8;
    allow 192.168.0.0/16;
    deny all;
    
    proxy_pass http://umbraco_backend;
}