CVE-2024-56156: Halo File Upload Auth Bypass Vulnerability

CVE-2024-56156 Overview

CVE-2024-56156 is a file type validation bypass vulnerability affecting Halo, an open source website building tool. Prior to version 2.20.13, this vulnerability allows attackers to circumvent file type validation controls, enabling the upload of malicious files including executables and HTML files. This bypass can lead to stored cross-site scripting (XSS) attacks and potential remote code execution under certain circumstances.

Critical Impact

Attackers can bypass file upload restrictions to deliver malicious payloads, potentially leading to stored XSS attacks and remote code execution on vulnerable Halo installations.

Affected Products

• Halo versions prior to 2.20.13
• Halo open source website building tool (all affected versions)

Discovery Timeline

• 2025-04-25 - CVE-2024-56156 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2024-56156

Vulnerability Analysis

This vulnerability (CWE-79) stems from insufficient file type validation in the Halo platform's file upload functionality. The application fails to properly validate and restrict file types during the upload process, allowing attackers to bypass security controls designed to prevent malicious file uploads.

When exploited, an attacker can upload files that would normally be blocked by the application's file type restrictions. This includes HTML files containing malicious JavaScript code and potentially executable files. The uploaded HTML files can execute scripts in the context of other users' browsers when accessed, resulting in stored XSS attacks. In more severe scenarios, the ability to upload executable content could lead to remote code execution on the server.

Root Cause

The root cause of this vulnerability lies in inadequate file type validation mechanisms within Halo's file upload handling code. The application does not properly verify file types through multiple validation layers (such as MIME type checking, file extension validation, and content inspection), allowing attackers to craft requests that bypass the intended restrictions.

Attack Vector

This vulnerability is exploitable over the network without requiring any privileges or user interaction. An attacker can craft specially formatted file upload requests to the vulnerable Halo instance, bypassing the file type validation controls. The attack chain typically involves:

1. Identifying a Halo instance running a vulnerable version (prior to 2.20.13)
2. Crafting a malicious file upload request with manipulated file metadata
3. Uploading malicious content such as HTML files with embedded JavaScript
4. Triggering the stored XSS when other users access the uploaded content

For detailed technical information about the vulnerability mechanics, refer to the GitHub Security Advisory and the associated commit fix.

Detection Methods for CVE-2024-56156

Indicators of Compromise

• Presence of unexpected HTML, JavaScript, or executable files in upload directories
• Suspicious file upload requests with manipulated Content-Type headers or file extensions
• Evidence of stored XSS execution in application logs or user reports
• Anomalous file upload activity from unauthenticated or low-privilege users

Detection Strategies

• Monitor file upload endpoints for attempts to upload restricted file types with manipulated metadata
• Implement content inspection rules to detect HTML or script content in uploaded files regardless of extension
• Review web application firewall (WAF) logs for file upload bypass attempts
• Analyze server-side logs for file creation events with suspicious extensions in upload directories

Monitoring Recommendations

• Enable detailed logging for all file upload operations in Halo
• Configure alerting for file uploads containing executable or script content
• Monitor for user reports of unexpected behavior that may indicate XSS execution
• Regularly audit uploaded files for potentially malicious content

How to Mitigate CVE-2024-56156

Immediate Actions Required

• Upgrade Halo to version 2.20.13 or later immediately
• Review and remove any suspicious files from upload directories
• Implement additional file upload restrictions at the web server or WAF level
• Audit user accounts for signs of compromise from potential XSS attacks

Patch Information

Halo has released version 2.20.13 which addresses this vulnerability. The fix was implemented through Pull Request #7149 and committed as 24f8d7b5. Organizations running affected versions should upgrade immediately by following the official Halo upgrade documentation.

For complete details on the security fix, see the GitHub Security Advisory GHSA-99mc-ch53-pqh9.

Workarounds

• Implement strict Content-Security-Policy headers to mitigate potential XSS impact
• Configure web server rules to block direct access to uploaded files or serve them with restrictive headers
• Use a Web Application Firewall (WAF) to inspect and block malicious file upload attempts
• Restrict file upload functionality to authenticated and authorized users only until patching is complete

# Example nginx configuration to add security headers for upload directory
location /uploads/ {
    add_header Content-Security-Policy "default-src 'none';" always;
    add_header X-Content-Type-Options "nosniff" always;
    add_header Content-Disposition "attachment" always;
}