PYSEC-2026-366

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Import Source

https://github.com/pypa/advisory-database/blob/main/vulns/jupyter-server/PYSEC-2026-366.yaml

JSON Data

https://api.osv.dev/v1/vulns/PYSEC-2026-366

Aliases

CVE-2026-44727
GHSA-fcw5-x6j4-ccmp

Published

2026-06-29T11:50:52.185377Z

Modified

2026-06-29T12:15:23.602664022Z

Severity

9.3 (Critical) CVSS_V4 - 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 CVSS Calculator

Summary

Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

Details

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.

Impact

An authenticated victim who navigates to /nbconvert/html/<path> containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.

Patches

Fixed in v2.20.0, commit 6cbee8d

Workarounds

For deployments where editing the installed jupyterserver is impractical (containerized builds, read-only images), adding this to jupyterserver_config.py has the same effect as the patch above without touching source files:

import jupyter_server.nbconvert.handlers as _nb

def _csp(self):
    return super(type(self), self).content_security_policy + "; sandbox allow-scripts"

_nb.NbconvertFileHandler.content_security_policy = property(_csp)
_nb.NbconvertPostHandler.content_security_policy = property(_csp)

References

Affected packages

PyPI / jupyter-server

Package

Name: jupyter-server; View open source insights on deps.dev
Purl: pkg:pypi/jupyter-server

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0Unknown introduced version / All previous versions are affected

Fixed

2.20.0

Affected versions

0.*

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.*

1.0.0rc0

1.0.0rc1

1.0.0rc2

1.0.0rc3

1.0.0rc4

1.0.0rc5

1.0.0rc6

1.0.0rc7

1.0.0rc8

1.0.0rc9

1.0.0rc10

1.0.0rc11

1.0.0rc12

1.0.0rc13

1.0.0rc14

1.0.0rc15

1.0.0rc16

1.0.0

1.0.1

1.0.2

1.0.3

1.0.4

1.0.5

1.0.6

1.0.7

1.0.8

1.0.9

1.0.10

1.0.11

1.1.0

1.1.1

1.1.2

1.1.3

1.1.4

1.2.0

1.2.1

1.2.2

1.2.3

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

1.7.0a1

1.7.0a2

1.7.0

1.8.0

1.9.0

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

1.21.0

1.23.0

1.23.1

1.23.2

1.23.3

1.23.4

1.23.5

1.23.6

1.24.0

2.*

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

2.0.0

2.0.1

2.0.2

2.0.3

2.0.4

2.0.5

2.0.6

2.0.7

2.1.0

2.2.0

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

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

Database specific

last_known_affected_version_range

"<= 2.19.0"

source

"https://github.com/pypa/advisory-database/blob/main/vulns/jupyter-server/PYSEC-2026-366.yaml"