CVE-2025-10755: Selleo Mentingo Auth Bypass Vulnerability

CVE-2025-10755 Overview

CVE-2025-10755 is an unrestricted file upload vulnerability in Selleo Mentingo version 2025.08.27. The flaw resides in the Content-Type handler component and is triggered through manipulation of the userAvatar argument. An authenticated remote attacker with low privileges can upload arbitrary files by bypassing content-type validation. The vulnerability is classified under [CWE-284] (Improper Access Control). A public exploit is available, and the vendor did not respond to disclosure attempts.

Critical Impact

Authenticated remote attackers can upload arbitrary files through the userAvatar parameter, potentially leading to malicious content hosting or further compromise of the application environment.

Affected Products

• Selleo Mentingo 2025.08.27
• Deployments exposing the user avatar upload endpoint
• Instances using the affected Content-Type Handler component

Discovery Timeline

• 2025-09-20 - CVE-2025-10755 published to NVD
• 2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-10755

Vulnerability Analysis

The vulnerability exists in the Content-Type handler used by Selleo Mentingo when processing avatar uploads. The application fails to properly validate or restrict the file type submitted through the userAvatar parameter. Attackers can supply arbitrary files by manipulating the request content type, bypassing the intended image-only upload restriction.

The root weakness maps to [CWE-284] Improper Access Control. Because the handler does not enforce strict validation of the uploaded object, the application accepts files outside the intended scope. Exploitation requires only low-level authenticated access and can be executed remotely over the network.

A public proof-of-concept is available via a GitHub Gist code snippet, increasing the risk of opportunistic exploitation. Additional technical context is tracked in VulDB entry #325069.

Root Cause

The underlying cause is insufficient validation of uploaded content in the userAvatar handler. The application trusts the client-supplied Content-Type header or fails to enforce server-side file type checks. This allows non-image payloads to be persisted in the avatar storage path.

Attack Vector

Exploitation requires network access and a valid low-privileged account. The attacker sends a crafted multipart upload request targeting the avatar endpoint with a manipulated Content-Type header. No user interaction is required. The vulnerability mechanism is described in the referenced public proof-of-concept; refer to the GitHub Gist for the technical exploitation details.

Detection Methods for CVE-2025-10755

Indicators of Compromise

• Unexpected non-image files stored in the avatar upload directory
• Avatar upload requests carrying mismatched extensions and MIME types
• HTTP POST requests to the avatar endpoint with abnormally large payloads or executable content signatures
• Access log entries showing avatar files being requested with script or archive extensions

Detection Strategies

• Inspect web server and application logs for POST requests to the userAvatar endpoint with non-image Content-Type values
• Perform file-type verification (magic byte inspection) on all files stored in avatar directories
• Correlate authenticated user sessions with anomalous upload activity, such as multiple avatar changes in a short window

Monitoring Recommendations

• Enable verbose logging on the upload handler and forward events to a central SIEM for correlation
• Alert on any file written to the avatar directory whose extension or content does not match an allowlisted image format
• Monitor outbound requests originating from the web server that could indicate secondary payload retrieval

How to Mitigate CVE-2025-10755

Immediate Actions Required

• Restrict access to the avatar upload endpoint to trusted user segments where feasible
• Deploy a web application firewall rule blocking uploads with Content-Type values that do not match the allowlisted image types
• Audit the avatar storage directory for unauthorized files and remove any that fail image validation
• Rotate credentials for accounts observed uploading suspicious avatar files

Patch Information

No vendor patch has been published. The vendor was contacted about the disclosure but did not respond. Consult the VulDB advisory for status updates and monitor the Selleo Mentingo release channel for future fixes.

Workarounds

• Enforce server-side validation of uploaded files using magic byte inspection rather than trusting client-supplied Content-Type headers
• Store uploaded avatars outside the web root or serve them from a domain that does not execute scripts
• Apply strict file size limits and reject files with double extensions or executable content signatures
• Disable the avatar upload feature until a vendor fix or compensating control is deployed

# Example nginx configuration to prevent script execution in the avatar directory
location /uploads/avatars/ {
    types { } 
    default_type application/octet-stream;
    add_header Content-Disposition "attachment";
    add_header X-Content-Type-Options "nosniff";
}