CVE-2026-40265: Note Mark Information Disclosure Flaw

CVE-2026-40265 Overview

Note Mark is an open-source note-taking application that allows users to create and organize notes within "books." A missing authentication vulnerability exists in versions 0.19.1 and prior where the asset download endpoint at /api/notes/{noteID}/assets/{assetID} is registered without authentication middleware, and the backend query does not verify ownership or book visibility. This allows unauthenticated users who know valid note and asset IDs to retrieve private note assets without authorization.

Critical Impact

An unauthenticated attacker can access and download private note assets including sensitive documents, images, and other attachments stored within Note Mark, regardless of whether the associated book is configured as public or private.

Affected Products

• Note Mark versions 0.19.1 and prior

Discovery Timeline

• 2026-04-17 - CVE CVE-2026-40265 published to NVD
• 2026-04-17 - Last updated in NVD database

Technical Details for CVE-2026-40265

Vulnerability Analysis

This vulnerability is classified as CWE-862 (Missing Authorization). The core issue lies in the improper implementation of access controls for the asset retrieval functionality within Note Mark. The /api/notes/{noteID}/assets/{assetID} endpoint was designed to serve note attachments but was inadvertently configured without the necessary authentication middleware that protects other sensitive API endpoints.

The vulnerability requires the attacker to know or enumerate valid note IDs and asset IDs. While this represents a degree of attack complexity, once these identifiers are obtained (potentially through other enumeration techniques or social engineering), complete bypass of the authorization model is possible. The confidentiality impact is significant as attackers can retrieve any stored asset regardless of the intended access restrictions.

Root Cause

The root cause of this vulnerability is the absence of authentication middleware registration on the asset download endpoint. When the API route was defined, the middleware responsible for validating user sessions and verifying access permissions was not included in the route configuration. Additionally, the backend database query that retrieves asset data does not include ownership or visibility checks, meaning it returns assets without validating that the requesting user has appropriate permissions to access the associated note or book.

Attack Vector

The attack vector for this vulnerability is network-based. An unauthenticated remote attacker can directly request the vulnerable endpoint over HTTP/HTTPS. The attack requires knowledge of valid noteID and assetID parameters. These identifiers could potentially be obtained through:

• Enumeration attacks against predictable ID patterns
• Information disclosure in error messages or logs
• Social engineering or insider knowledge
• Analysis of shared links or exported content

Once valid IDs are obtained, the attacker simply constructs a GET request to /api/notes/{noteID}/assets/{assetID} and receives the full content of the private asset in the response, completely bypassing the intended authorization controls.

Detection Methods for CVE-2026-40265

Indicators of Compromise

• Unusual access patterns to /api/notes/*/assets/* endpoints from unauthenticated sessions
• High volume of asset download requests without corresponding authentication cookies or tokens
• Sequential or enumeration-style requests to asset endpoints from single IP addresses
• Asset access logs showing downloads without associated user sessions

Detection Strategies

• Implement monitoring rules to detect unauthenticated requests to the asset download endpoint
• Configure web application firewalls to alert on suspicious patterns targeting /api/notes/{noteID}/assets/{assetID} paths
• Review web server access logs for requests to asset endpoints that lack session identifiers or authentication headers
• Deploy anomaly detection to identify unusual download volumes or access patterns

Monitoring Recommendations

• Enable detailed logging for all API requests to asset endpoints including authentication status
• Set up alerts for failed authentication attempts followed by direct asset endpoint access
• Monitor for enumeration patterns in noteID and assetID request parameters
• Track asset download metrics and investigate unexpected spikes in unauthenticated access

How to Mitigate CVE-2026-40265

Immediate Actions Required

• Upgrade Note Mark to version 0.19.2 or later immediately
• Audit access logs to determine if unauthorized asset access has occurred
• Review any sensitive assets stored in Note Mark for potential exposure
• Consider regenerating or rotating any sensitive content that may have been accessed

Patch Information

The vulnerability has been fixed in Note Mark version 0.19.2. The fix involves properly registering authentication middleware on the asset download endpoint and implementing ownership validation in the backend query. For detailed information about the changes, see the GitHub Security Advisory GHSA-p5w6-75f9-cc2p. The specific fix can be reviewed in the GitHub commit, and the patched release is available at GitHub Release v0.19.2.

Workarounds

• If immediate upgrade is not possible, consider placing a reverse proxy with authentication in front of the Note Mark application
• Implement network-level access controls to restrict access to the Note Mark instance to trusted networks only
• Configure web server rules to require authentication for all requests to /api/notes/*/assets/* paths
• Temporarily disable or restrict asset upload functionality until the patch can be applied