CVE-2026-31876: Notesnook has Stored XSS via unsanitized Twitter/X embed URL in editor (`tweetToEmbed`)

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-11 · updated 2026-06-17
Weakness: CWE-79

Description

Notesnook is a note-taking app focused on user privacy & ease of use. Prior to 3.3.9, a Stored Cross-Site Scripting (XSS) vulnerability existed in Notesnook's editor embed component when rendering Twitter/X embed URLs. The tweetToEmbed() function in component.tsx interpolated the user-supplied URL directly into an HTML string without escaping, which was then assigned to the srcdoc attribute of an <iframe>. This vulnerability is fixed in 3.3.9.

Affected products

streetwriters Notesnook Web/Desktop: before 3.3.9 — fixed in 3.3.9
streetwriters notesnook: before 3.3.15 — fixed in 3.3.15

How to fix

Upgrade to a fixed version: streetwriters Notesnook Web/Desktop 3.3.9; streetwriters notesnook 3.3.15. Check the vendor advisory for mitigations.

References

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