{"id":"CVE-2026-44727","aliases":["DEBIAN-CVE-2026-44727","EUVD-2026-38347","GHSA-fcw5-x6j4-ccmp","OESA-2026-3954","OESA-2026-3955","OESA-2026-3956","PYSEC-2026-366","UBUNTU-CVE-2026-44727","openSUSE-SU-2026:11159-1"],"status":"published","title":"Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP","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.","severity":{"version":"4.0","score":9.3,"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","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00438,"percentile":0.38524,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1021","CWE-79"],"published":"2026-06-18T15:04:07Z","modified":"2026-10-28T02:31:07Z","fixes":[{"ecosystem":"PyPI","package":"jupyter-server","fixed_in":["2.20.0"],"sources":["ghsa","osv"]},{"ecosystem":"Debian:14","package":"jupyter-server","fixed_in":["2.20.0-1"],"sources":["osv"]},{"ecosystem":"openEuler:24.03-LTS-SP1","package":"python-jupyter-server","fixed_in":["2.13.0-3.oe2403sp1"],"sources":["osv"]},{"ecosystem":"openEuler:24.03-LTS-SP3","package":"python-jupyter-server","fixed_in":["2.13.0-3.oe2403sp3"],"sources":["osv"]},{"ecosystem":"openEuler:24.03-LTS-SP4","package":"python-jupyter-server","fixed_in":["2.13.0-3.oe2403sp4"],"sources":["osv"]},{"ecosystem":"openSUSE:Tumbleweed","package":"python-jupyter-server","fixed_in":["2.20.0-1.1"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"2.19.0"},{"fixed":"2.20.0"}]}]},{"source":"osv","ecosystem":"Debian:12","package":"jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.23.3-1","1.23.3-2","2.14.0-1","2.14.2-1","2.14.2-2","2.14.2-3","2.14.2-4","2.14.2-5","2.15.0-1","2.17.0-1","2.20.0-1","2.20.0-2","2.20.0-3","2.9.1-1"]},{"source":"osv","ecosystem":"Debian:13","package":"jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.15.0-1","2.17.0-1","2.20.0-1","2.20.0-2","2.20.0-3"]},{"source":"osv","ecosystem":"Debian:14","package":"jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.20.0-1"}]}],"versions":["2.15.0-1","2.17.0-1"]},{"source":"osv","ecosystem":"PyPI","package":"jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.20.0"}]}],"versions":["0.0.0","0.0.1","0.0.2","0.0.3","0.0.4","0.0.5","0.1.0","0.1.1","0.2.0","0.2.1","0.3.0","1.0.0","1.0.0rc0","1.0.0rc1","1.0.0rc10","1.0.0rc11","1.0.0rc12","1.0.0rc13","1.0.0rc14","1.0.0rc15","1.0.0rc16","1.0.0rc2","1.0.0rc3","1.0.0rc4","1.0.0rc5","1.0.0rc6","1.0.0rc7","1.0.0rc8","1.0.0rc9","1.0.1","1.0.10","1.0.11","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.0.7","1.0.8","1.0.9","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.10.0","1.10.1","1.10.2","1.11.0","1.11.1","1.11.2","1.12.0","1.12.1","1.13.0","1.13.1","1.13.2","1.13.3","1.13.4","1.13.5","1.15.0","1.15.1","1.15.2","1.15.3","1.15.4","1.15.5","1.15.6","1.16.0","1.17.0","1.17.1","1.18.0","1.18.1","1.19.0","1.19.1","1.2.0","1.2.1","1.2.2","1.2.3","1.21.0","1.23.0","1.23.1","1.23.2","1.23.3","1.23.4","1.23.5","1.23.6","1.24.0","1.3.0","1.4.0","1.4.1","1.5.0","1.5.1","1.6.0","1.6.1","1.6.2","1.6.3","1.6.4","1.7.0","1.7.0a1","1.7.0a2","1.8.0","1.9.0","2.0.0","2.0.0a0","2.0.0a1","2.0.0a2","2.0.0b0","2.0.0b1","2.0.0rc0","2.0.0rc1","2.0.0rc2","2.0.0rc3","2.0.0rc4","2.0.0rc5","2.0.0rc6","2.0.0rc7","2.0.0rc8","2.0.1","2.0.2","2.0.3","2.0.4","2.0.5","2.0.6","2.0.7","2.1.0","2.10.0","2.10.1","2.11.0","2.11.1","2.11.2","2.12.0","2.12.1","2.12.2","2.12.3","2.12.4","2.12.5","2.13.0","2.14.0","2.14.1","2.14.2","2.15.0","2.16.0","2.17.0","2.18.0","2.18.1","2.18.2","2.19.0","2.2.0","2.2.1","2.3.0","2.4.0","2.5.0","2.6.0","2.7.0","2.7.1","2.7.2","2.7.3","2.8.0","2.9.0","2.9.1"]},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP1","package":"python-jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.13.0-3.oe2403sp1"}]}]},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP3","package":"python-jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.13.0-3.oe2403sp3"}]}]},{"source":"osv","ecosystem":"openEuler:24.03-LTS-SP4","package":"python-jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.13.0-3.oe2403sp4"}]}]},{"source":"osv","ecosystem":"PyPI","package":"jupyter-server","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.20.0"}]}],"versions":["0.0.0","0.0.1","0.0.2","0.0.3","0.0.4","0.0.5","0.1.0","0.1.1","0.2.0","0.2.1","0.3.0","1.0.0","1.0.0rc0","1.0.0rc1","1.0.0rc10","1.0.0rc11","1.0.0rc12","1.0.0rc13","1.0.0rc14","1.0.0rc15","1.0.0rc16","1.0.0rc2","1.0.0rc3","1.0.0rc4","1.0.0rc5","1.0.0rc6","1.0.0rc7","1.0.0rc8","1.0.0rc9","1.0.1","1.0.10","1.0.11","1.0.2","1.0.3","1.0.4","1.0.5","1.0.6","1.0.7","1.0.8","1.0.9","1.1.0","1.1.1","1.1.2","1.1.3","1.1.4","1.10.0","1.10.1","1.10.2","1.11.0","1.11.1","1.11.2","1.12.0","1.12.1","1.13.0","1.13.1","1.13.2","1.13.3","1.13.4","1.13.5","1.15.0","1.15.1","1.15.2","1.15.3","1.15.4","1.15.5","1.15.6","1.16.0","1.17.0","1.17.1","1.18.0","1.18.1","1.19.0","1.19.1","1.2.0","1.2.1","1.2.2","1.2.3",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hat","product":"red hat migration toolkit for applications 8.2"},{"vendor":"red hat","product":"red hat openshift ai (rhoai)"},{"vendor":"red hat","product":"red hat openshift ai 3.4"}],"references":[{"url":"https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp","tags":["x_refsource_CONFIRM","Mitigation","Patch","Vendor Advisory","advisory","web","report"]},{"url":"https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd","tags":["x_refsource_MISC","Patch","fix","web","report"]},{"url":"https://access.redhat.com/security/cve/CVE-2026-44727","tags":["vdb-entry","x_refsource_REDHAT","advisory","web"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2491516","tags":["issue-tracking","x_refsource_REDHAT","report","web"]},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json","tags":["x_sadp-csaf-vex","web"]},{"url":"https://access.redhat.com/errata/RHSA-2026:43038","tags":["vendor-advisory","x_refsource_REDHAT","advisory","web"]},{"url":"https://access.redhat.com/errata/RHSA-2026:60520","tags":["vendor-advisory","x_refsource_REDHAT","advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44727","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-fcw5-x6j4-ccmp","tags":["advisory"]},{"url":"https://github.com/jupyter-server/jupyter_server","tags":["package"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/jupyter-server/PYSEC-2026-366.yaml","tags":["web"]},{"url":"https://pypi.org/project/jupyter-server","tags":["web","package"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44727.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-44727","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-3954","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-3955","tags":["advisory"]},{"url":"https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-3956","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-44727","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-44727","tags":["report"]},{"url":"","tags":["advisory"]},{"url":"https://www.suse.com/security/cve/CVE-2026-44727","tags":["web"]}],"sources":{"cve":[{"id":"CVE-2026-44727","title":"Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP","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.","status":"published","published":"2026-06-22T19:56:56.776Z","modified":"2026-08-28T12:04:25.625Z","cvss":[{"version":"4.0","score":9.3,"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","level":"critical","assessor":"cna"},{"version":"3.1","score":9,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H","level":"critical","assessor":"adp"}],"cwes":["CWE-79","CWE-1021","CWE-79"],"updated_at":"2026-11-02T13:43:00.288193Z"}],"euvd":[{"id":"EUVD-2026-38347","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.","status":"published","published":"2026-06-22T19:56:56Z","modified":"2026-08-28T12:04:25Z","cvss":[{"version":"4.0","score":9.3,"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","level":"critical"}],"updated_at":"2026-11-02T18:01:23.608347Z"}],"ghsa":[{"id":"GHSA-fcw5-x6j4-ccmp","title":"Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP ","description":"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`. \n\nCombined 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.\n\n### Impact\n\nAn authenticated victim who navigates to `/nbconvert/html/\u003cpath\u003e` containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.\n\n### Patches\n\nFixed in v2.20.0, commit [6cbee8d](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)\n\n\n### Workarounds\n\nFor deployments where editing the installed jupyter_server is impractical (containerized builds, read-only images), adding this to jupyter_server_config.py has the same effect as the patch above without touching source files:\n\n```\nimport jupyter_server.nbconvert.handlers as _nb\n\ndef _csp(self):\n    return super(type(self), self).content_security_policy + \"; sandbox allow-scripts\"\n\n_nb.NbconvertFileHandler.content_security_policy = property(_csp)\n_nb.NbconvertPostHandler.content_security_policy = property(_csp)\n```","status":"published","published":"2026-06-18T15:04:07Z","modified":"2026-08-28T18:31:11Z","cvss":[{"version":"4.0","score":9.3,"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","level":"critical"},{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-79","CWE-1021"],"updated_at":"2026-11-02T14:41:08.084849Z"}],"nvd":[{"id":"CVE-2026-44727","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.","status":"published","published":"2026-06-22T21:16:24.26Z","modified":"2026-10-25T23:10:00.167Z","cvss":[{"version":"4.0","score":9.3,"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical","assessor":"secondary"},{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"primary"},{"version":"3.1","score":9,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H","level":"critical","assessor":"secondary"}],"cwes":["CWE-79","CWE-1021"],"updated_at":"2026-11-02T14:12:25.288279Z"}],"osv":[{"id":"CVE-2026-44727","title":"Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP","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.","status":"published","published":"2026-06-22T19:56:56.776Z","modified":"2026-10-28T02:31:07.724736981Z","cvss":[{"version":"4.0","score":9.3,"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","level":"critical"}],"cwes":["CWE-1021","CWE-79"],"updated_at":"2026-11-02T15:45:05.172514Z"},{"id":"DEBIAN-CVE-2026-44727","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.","status":"published","published":"2026-06-22T21:16:24.26Z","modified":"2026-10-26T11:47:33.241471944Z","cvss":[{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:45:55.669088Z"},{"id":"GHSA-fcw5-x6j4-ccmp","title":"Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP ","description":"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`. \n\nCombined 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.\n\n### Impact\n\nAn authenticated victim who navigates to `/nbconvert/html/\u003cpath\u003e` containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.\n\n### Patches\n\nFixed in v2.20.0, commit [6cbee8d](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)\n\n\n### Workarounds\n\nFor deployments where editing the installed jupyter_server is impractical (containerized builds, read-only images), adding this to jupyter_server_config.py has the same effect as the patch above without touching source files:\n\n```\nimport jupyter_server.nbconvert.handlers as _nb\n\ndef _csp(self):\n    return super(type(self), self).content_security_policy + \"; sandbox allow-scripts\"\n\n_nb.NbconvertFileHandler.content_security_policy = property(_csp)\n_nb.NbconvertPostHandler.content_security_policy = property(_csp)\n```","status":"published","published":"2026-06-18T15:04:07Z","modified":"2026-09-10T03:50:49.418798509Z","cvss":[{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","level":"medium"},{"version":"4.0","score":9.3,"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","level":"critical"}],"cwes":["CWE-1021","CWE-79"],"updated_at":"2026-11-02T15:46:46.39441Z"},{"id":"OESA-2026-3954","title":"python-jupyter-server security update","description":"The backend for Jupyter web applications\r\n\r\nSecurity Fix(es):\n\nThe 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`\u0026apos;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. An authenticated victim who navigates to `/nbconvert/html/\u0026lt;path\u0026gt;` containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.(CVE-2026-44727)","status":"published","published":"2026-09-20T13:23:33Z","modified":"2026-09-20T13:30:27.871601749Z","cvss":[{"version":"4.0","score":9.3,"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical"}],"updated_at":"2026-11-02T15:52:47.643553Z"},{"id":"OESA-2026-3955","title":"python-jupyter-server security update","description":"The backend for Jupyter web applications\r\n\r\nSecurity Fix(es):\n\nThe 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`\u0026apos;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. An authenticated victim who navigates to `/nbconvert/html/\u0026lt;path\u0026gt;` containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.(CVE-2026-44727)","status":"published","published":"2026-09-20T13:23:33Z","modified":"2026-09-20T13:30:30.109937104Z","cvss":[{"version":"4.0","score":9.3,"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical"}],"updated_at":"2026-11-02T15:52:47.643553Z"},{"id":"OESA-2026-3956","title":"python-jupyter-server security update","description":"The backend for Jupyter web applications\r\n\r\nSecurity Fix(es):\n\nThe 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`\u0026apos;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. An authenticated victim who navigates to `/nbconvert/html/\u0026lt;path\u0026gt;` containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.(CVE-2026-44727)","status":"published","published":"2026-09-20T13:23:34Z","modified":"2026-09-20T13:30:30.305236853Z","cvss":[{"version":"4.0","score":9.3,"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical"}],"updated_at":"2026-11-02T15:52:47.643553Z"},{"id":"PYSEC-2026-366","title":"Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP ","description":"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`. \n\nCombined 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.\n\n### Impact\n\nAn authenticated victim who navigates to `/nbconvert/html/\u003cpath\u003e` containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.\n\n### Patches\n\nFixed in v2.20.0, commit [6cbee8d](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)\n \n\n### Workarounds\n\nFor deployments where editing the installed jupyter_server is impractical (containerized builds, read-only images), adding this to jupyter_server_config.py has the same effect as the patch above without touching source files:\n\n```\nimport jupyter_server.nbconvert.handlers as _nb\n\ndef _csp(self):\n    return super(type(self), self).content_security_policy + \"; sandbox allow-scripts\"\n\n_nb.NbconvertFileHandler.content_security_policy = property(_csp)\n_nb.NbconvertPostHandler.content_security_policy = property(_csp)\n```","status":"published","published":"2026-06-29T11:50:52.185377Z","modified":"2026-07-13T16:15:26.84139676Z","cvss":[{"version":"4.0","score":9.3,"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","level":"critical"}],"updated_at":"2026-11-02T15:52:56.847083Z"},{"id":"UBUNTU-CVE-2026-44727","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.","status":"published","published":"2026-06-22T21:16:00Z","modified":"2026-10-17T12:58:20.802623457Z","cvss":[{"version":"4.0","score":9.3,"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","level":"critical"},{"version":"3.1","score":9,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H","level":"critical"},{"version":"3.1","score":5.4,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T16:56:26.396868Z"},{"id":"openSUSE-SU-2026:11159-1","title":"python311-jupyter-server-2.20.0-1.1 on GA media","description":"These are all security issues fixed in the python311-jupyter-server-2.20.0-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-06-30T00:00:00Z","modified":"2026-07-01T09:45:08.829389104Z","updated_at":"2026-11-02T16:58:38.95195Z"}]}}