CVE-2026-25737: Budibase Path Traversal Vulnerability

CVE-2026-25737 Overview

CVE-2026-25737 is an arbitrary file upload vulnerability affecting Budibase, a low code platform for creating internal tools, workflows, and admin panels. In versions 3.24.0 and earlier, attackers can bypass file extension restrictions that are enforced only at the UI level, allowing the upload of malicious files to the server.

Critical Impact

Attackers can bypass client-side file upload restrictions to upload arbitrary malicious files, potentially leading to remote code execution, data exfiltration, or complete system compromise.

Affected Products

• Budibase version 3.24.0 and earlier

Discovery Timeline

• 2026-03-09 - CVE CVE-2026-25737 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2026-25737

Vulnerability Analysis

This vulnerability represents a classic Client-Side Enforcement of Server-Side Security issue (CWE-602). The Budibase platform implements file extension restrictions to prevent the upload of potentially dangerous file types; however, these restrictions are enforced exclusively through client-side JavaScript validation in the user interface rather than on the server-side.

When a user attempts to upload a file through the Budibase interface, the application checks the file extension against a whitelist of allowed types. However, because this validation occurs only in the browser, an attacker can trivially bypass these controls by intercepting and modifying the HTTP request directly, using tools such as a proxy or by crafting custom API requests.

Once bypassed, attackers can upload files with dangerous extensions such as .php, .jsp, .aspx, or other executable formats depending on the underlying server configuration. These uploaded files may then be executed on the server, leading to remote code execution.

Root Cause

The root cause of CVE-2026-25737 is the reliance on client-side validation for security-critical file upload restrictions. The application fails to implement server-side validation of file extensions and content types, trusting that the client-side UI controls will prevent malicious uploads. This violates the fundamental security principle of never trusting client-supplied input.

Attack Vector

The attack vector is network-based and requires low-privilege authenticated access to a Budibase instance. An attacker with basic user permissions can:

1. Identify a file upload functionality within the Budibase application
2. Attempt to upload a restricted file type through the normal UI (which will be blocked)
3. Intercept the upload request using a proxy tool like Burp Suite
4. Modify the request to change the file extension or bypass client-side checks entirely
5. Forward the modified request to the server, which accepts the malicious file

The vulnerability requires some user interaction as the attacker must have an authenticated session. However, once exploited, the impact can extend beyond the original security context, potentially affecting other users and system components.

Detection Methods for CVE-2026-25737

Indicators of Compromise

• Unexpected file types appearing in Budibase upload directories (e.g., .php, .jsp, .exe, .sh files)
• Web server logs showing requests to uploaded files with executable extensions
• Unusual outbound network connections from the Budibase server
• Presence of webshells or backdoor scripts in storage directories

Detection Strategies

• Monitor file upload directories for unexpected file extensions that should be restricted
• Implement file integrity monitoring on Budibase storage locations
• Analyze HTTP request logs for file upload requests with suspicious content types or extension mismatches
• Deploy web application firewall (WAF) rules to detect file upload bypass attempts

Monitoring Recommendations

• Enable verbose logging for all file upload operations in Budibase
• Configure alerting for any executable file uploads to the Budibase server
• Implement real-time monitoring of storage directories with hash-based change detection
• Review access logs for API calls that bypass the standard UI workflow

How to Mitigate CVE-2026-25737

Immediate Actions Required

• Upgrade Budibase to a patched version as soon as one is available from the vendor
• Implement server-side file extension validation as an additional security layer
• Configure the web server to prevent execution of uploaded files regardless of extension
• Restrict file upload directories with appropriate permissions and disable script execution

Patch Information

Users should monitor the GitHub Security Advisory for official patch information and upgrade instructions. Apply vendor patches immediately when available.

Workarounds

• Deploy a web application firewall (WAF) with rules to validate file extensions on upload requests at the network level
• Configure the web server to serve all uploaded files with Content-Type: application/octet-stream and Content-Disposition: attachment headers to prevent execution
• Isolate the Budibase file storage directory from the web root and disable script execution in storage locations
• Implement network segmentation to limit potential impact if the vulnerability is exploited

# Example: Disable script execution in upload directory (Apache)
<Directory "/path/to/budibase/uploads">
    Options -ExecCGI
    php_flag engine off
    <FilesMatch "\.(php|phtml|php3|php4|php5|pl|py|jsp|asp|aspx|sh|cgi)$">
        Require all denied
    </FilesMatch>
</Directory>