Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP_CVE-2026-44727

{
    "lastseen": "",
    "description": "Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy. Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.",
    "published": "2026-06-22T19:56:56.776Z",
    "modified": "2026-06-22T19:56:56.776Z",
    "type": "cve",
    "title": "Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP",
    "source": "GitHub_M",
    "references": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp\nhttps://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd",
    "id": "CVE-2026-44727",
    "bulletinFamily": "",
    "cwe": [
        "CWE-79",
        "CWE-1021"
    ],
    "cvelist": null,
    "sourceData": "jupyter-server jupyter_server < 2.20",
    "sourceHref": "",
    "cvss": {
        "score": 9.3,
        "severity": "CRITICAL",
        "vector": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "jupyter_server",
    "version": "< 2.20",
    "vendor": "jupyter-server",
    "ai_description": "Stored XSS vulnerability in Jupyter Server via missing sandbox CSP, allowing kernel RCE and cookie access",
    "ai_severity": "Critical",
    "ai_vendor": "Project Jupyter",
    "ai_product": "Jupyter Server",
    "ai_version": "< 2.20",
    "ai_score": 9.3
}