dbcve.org
Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-40171

HIGH · 8.4 CVSS v4.0 Published 2026-05-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
88/100
Remediation priority · High
Remotely reachable

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In Jupyter Notebook versions 7.0.0 through 7.5.5, JupyterLab versions 4.5.6 and earlier, and the corresponding @jupyter-notebook/help-extension and @jupyterlab/help-extension packages before 7.5.6 and 4.5.7, a stored cross-site scripting issue in the help command linker can be chained with attacker-controlled notebook content to steal authentication tokens with a single click. An attacker can craft a malicious notebook file containing elements that appear indistinguishable from legitimate controls and trigger execution when a user interacts with them. Successful exploitation allows theft of the user's authentication token and complete takeover of the Jupyter session through the REST API, including reading files, creating or modifying files, accessing kernels to execute arbitrary code, and creating terminals for shell access. This issue has been fixed in Notebook 7.5.6, JupyterLab 4.5.7, @jupyter-notebook/help-extension 7.5.6, and @jupyterlab/help-extension 4.5.7. As a workaround, disable the affected help extensions or set allowCommandLinker to false in the sanitizer configuration.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Stored XSS vulnerability in Jupyter Notebook (7.0.0-7.5.5) and JupyterLab (≤4.5.6) help command linker allows attackers to embed malicious content in notebooks that steals authentication tokens on user interaction, enabling full session takeover via REST API including file access, code execution, and terminal creation.

MitigationUpdate to Notebook 7.5.6, JupyterLab 4.5.7, or respective @jupyter-notebook/help-extension 7.5.6/@jupyterlab/help-extension 4.5.7; alternatively disable the help extensions or set allowCommandLinker to false in sanitizer configuration.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
High
Authentication
X
User interaction
A
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Jupyter Notebook version
    Run 'jupyter notebook --version' or check the package.json/version file in your Jupyter environment
    Affected if Version is 7.0.0 through 7.5.5 (inclusive)
  2. Identify JupyterLab version
    Run 'jupyterlab --version' or check the package.json/version file in your Jupyter environment
    Affected if Version is 4.5.6 or lower
  3. Confirm help extension is enabled in Notebook
    Check for @jupyter-notebook/help-extension package or look for the help menu functionality in the Notebook interface
    Affected if The help extension is loaded and functional in the Notebook UI
  4. Confirm help extension is enabled in JupyterLab
    Check for @jupyterlab/help-extension package or verify help menu items are available in JupyterLab
    Affected if The help extension is loaded and functional in JupyterLab
  5. Check allowCommandLinker sanitizer configuration
    Inspect Jupyter configuration files (jupyter_notebook_config.py or jupyter_lab_config.py) for the 'allowCommandLinker' setting in sanitizer configuration
    Affected if allowCommandLinker is not explicitly set to false (defaults to true, allowing the vulnerable behavior)

You are affected if you run Notebook 7.0.0-7.5.5 or JupyterLab ≤4.5.6 AND have the help extension enabled with allowCommandLinker not explicitly disabled.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update to Notebook 7.5.6, JupyterLab 4.5.7, or respective @jupyter-notebook/help-extension 7.5.6/@jupyterlab/help-extension 4.5.7; alternatively disable the help extensions or set allowCommandLinker to false in sanitizer configuration.

Recommended fix High confidence

Notebook 7.5.6, JupyterLab 4.5.7, @jupyter-notebook/help-extension 7.5.6, or @jupyterlab/help-extension 4.5.7 depending on component in use

  1. Identify which Jupyter component is affected: Jupyter Notebook, JupyterLab, or the help-extension packages
  2. For Jupyter Notebook: Run 'pip install --upgrade notebook==7.5.6' or 'conda install notebook=7.5.6' depending on your package manager
  3. For JupyterLab: Run 'pip install --upgrade jupyterlab==4.5.7' or 'conda install jupyterlab=4.5.7' depending on your package manager
  4. For @jupyter-notebook/help-extension: Run 'pip install --upgrade @jupyter-notebook/help-extension==7.5.6'
  5. For @jupyterlab/help-extension: Run 'pip install --upgrade @jupyterlab/help-extension==4.5.7'
  6. Restart the Jupyter server to apply the update
  7. Verify the fix by checking the installed version matches the fixed release

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-40171 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data