CVE-2026-33978: Notesnook: Stored XSS in mobile share editor via unescaped web clip title metadata

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-04-01 · updated 2026-10-26
Weakness: CWE-79

Description

Notesnook is a note-taking app focused on user privacy & ease of use. Prior to version 3.3.17, a stored XSS vulnerability exists in the mobile share / web clip flow because attacker-controlled clip metadata is concatenated into HTML without escaping and then rendered with innerHTML inside the mobile share editor WebView. An attacker can control the shared title metadata (for example through Android/iOS share metadata such as TITLE / SUBJECT, or through link-preview title data) and inject HTML such as </a><img src=x onerror=...>. When the victim opens the Notesnook share flow and selects Web clip, the payload is inserted into the generated HTML and executed in the mobile editor WebView. This issue has been patched in version 3.3.17.

Affected products

streetwriters notesnook: before 3.3.17 — fixed in 3.3.17

How to fix

Upgrade to a fixed version: streetwriters notesnook 3.3.17. Check the vendor advisory for mitigations.

References

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