CVE-2026-42090: Notesnook: RCE via stored XSS in note export rendering

Severity: critical (CVSS 9.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-04 · updated 2026-10-26
Weakness: CWE-79

Description

Notesnook is a note-taking app focused on user privacy & ease of use. Prior to Notesnook Web/Desktop version 3.3.15 and prior to Notesnook iOS/Android version 3.3.20, a stored XSS vulnerability in the note export flow can be escalated to remote code execution in the desktop app. The root cause is that exported note fields such as title, headline, and content are inserted into the generated HTML template without HTML escaping. When the note is later exported to PDF, Notesnook renders that HTML into a same-origin, unsandboxed iframe using iframe.srcdoc = .... Injected script executes in the Notesnook origin. In the desktop app, this becomes RCE because Electron is configured with nodeIntegration: true and contextIsolation: false. This issue has been patched in Notesnook Web/Desktop version 3.3.15 and Notesnook iOS/Android version 3.3.20.

Affected products

streetwriters Notesnook Web/Desktop: before 3.3.15 — fixed in 3.3.15
streetwriters notesnook: before 3.3.20 — fixed in 3.3.20

How to fix

Upgrade to a fixed version: streetwriters Notesnook Web/Desktop 3.3.15; streetwriters notesnook 3.3.20. Check the vendor advisory for mitigations.

References

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