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BREW-jupyterlab-CVE-2026-44727 — Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

Affected: Homebrew: jupyterlab

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](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)

### Workarounds

For 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:

``` 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) ```

CLEANSTART-2026-SY39659 — Security fix for CVE-2026-44727 applied in: tensorflow-gpu-jupyter 2.21.0-r8

Affected: CleanStart: tensorflow-gpu-jupyter

Security vulnerability affects the tensorflow-gpu-jupyter package. This issue is resolved in later releases. See references for vulnerability details.

EUVD-2026-361081

fkie_cve-2026-44727

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.

GHSA-fcw5-x6j4-ccmp — Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

Affected: PyPI: jupyter-server

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`.

### 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](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)

### Workarounds

``` 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) ```

OESA-2026-3954 — python-jupyter-server security update

Affected: openEuler:24.03-LTS-SP1: python-jupyter-server

The backend for Jupyter web applications Security Fix(es):

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. 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.(CVE-2026-44727)

openSUSE-SU-2026:11159-1 — python311-jupyter-server-2.20.0-1.1 on GA media

python311-jupyter-server-2.20.0-1.1 on GA media

PYSEC-2026-366 — Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

Affected: PyPI: jupyter-server

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`.

### 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](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)

### Workarounds

``` 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) ```

RHSA-2026:43038 — Red Hat Security Advisory: Migration Toolkit for Applications

jupyter-server: jupyter-server: Sensitive data exposure via path traversal vulnerability fast-uri: fast-uri: URI authority bypass due to improper delimiter handling fast-uri: fast-uri: Security policy bypass due to improper Unicode hostname canonicalization golang.org/x/net/html: golang.org/x/net/html: Arbitrary code execution via Cross-Site Scripting golang.org/x/net/html: golang: golang.org/x/net/html: Cross-Site Scripting via HTML parsing bypass python-dotenv: python-dotenv: Arbitrary file overwrite via symbolic link following mistune: Mistune: Regular Expression Denial of Service (ReDoS) via crafted Markdown input net: golang: Go net package: Denial of Service via long CNAME response in LookupCNAME aiohttp: AIOHTTP: Arbitrary code execution via untrusted input to CookieJar.load() jupyter-server: Jupyter Server: Unauthorized File Access via Path Traversal Vulnerability net/mail: golang: Go net/mail: Denial of Service via crafted email inputs golang.org/x/net/idna: golang: net/http: golang.org/x/net/idna: Privilege escalation via incorrect Punycode label processing jupyter-server: Jupyter Server: Cross-Origin Resource Sharing (CORS) bypass via improper Origin header validation Jupyter Notebook: JupyterLab: @jupyter-notebook/help-extension: @jupyterlab/help-extension: Jupyter Notebook and JupyterLab: Session takeover via stored cross-site scripting jupyterlab: JupyterLab: Arbitrary code execution due to improper enforcement of extension allow-list net/mail: golang: net/mail…

UBUNTU-CVE-2026-44727

Affected: Ubuntu:22.04:LTS: jupyter-server, Ubuntu:24.04:LTS: jupyter-server, Ubuntu:25.10: jupyter-server, Ubuntu:26.04:LTS: jupyter-server