Note Mark hat Stored XSS über unbeschränkten Asset-Upload

An attacker can exploit this XSS vulnerability by crafting a malicious HTML, SVG, or XHTML file and uploading it as a note asset. When a victim views this note, the attacker's code will execute within the context of the Note Mark application, allowing the attacker to perform actions as the victim. This could include stealing session cookies, modifying data, or redirecting the victim to a malicious website. The impact is amplified by the application's failure to properly sanitize uploaded files and serve them with appropriate content type headers, preventing browsers from correctly identifying and handling the content.

Organizations using Note Mark for internal collaboration or knowledge management are at risk, particularly those relying on older versions (0.19.0 - 0.19.2). Shared hosting environments where multiple users have access to the Note Mark instance are also at increased risk, as a compromised user could potentially exploit the vulnerability to affect other users.

• linux / server: Monitor Note Mark application logs for file uploads with suspicious content types (e.g., text/html, image/svg+xml) or unusual filenames. Use grep to search for patterns indicative of XSS payloads within uploaded files.

grep -r '<script' /var/log/notemark/upload.log

• generic web: Examine Note Mark's access logs for requests to asset endpoints with unusual parameters or user agents. Use curl to test asset endpoints with potentially malicious payloads.

curl -X POST -d '<script>alert("XSS")</script>' http://your-notemark-instance/assets/upload

1. 2026-04-16Disclosure

   disclosure

1. Reserviert2026-04-10
2. Veröffentlicht2026-04-16
3. Geändert2026-04-18
4. EPSS aktualisiert2026-04-24

The primary mitigation for CVE-2026-40262 is to immediately upgrade Note Mark to version 0.19.2 or later. If upgrading is not immediately feasible, consider implementing a Web Application Firewall (WAF) rule to block the upload of files with potentially malicious content types (HTML, SVG, XHTML). Additionally, review and strengthen input validation and output encoding practices within the application to prevent future XSS vulnerabilities. After upgrading, confirm the fix by attempting to upload a test HTML file and verifying that it is not rendered as executable code.