GHSA-mqcg-5x36-vfcg
CRITICALGHSA-mqcg-5x36-vfcg is a critical-severity (CVSS 9.6) remote code execution vulnerability in jupyterlab. O3 Security confirms whether GHSA-mqcg-5x36-vfcg is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
JupyterLab's command linker attributes in HTML enable one-click command execution from untrusted content
Real-World Exposure
jupyterlab🐍notebookReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
JupyterLab's HTML sanitizer allowlists data-commandlinker-command and data-commandlinker-args on button elements, while CommandLinker listens for all click events on document.body and executes the named command without checking whether the element came from trusted JupyterLab UI. A notebook with a pre-saved HTML cell output containing a deceptive button can trigger arbitrary JupyterLab commands - including arbitrary code execution - on a single user click, without any code being submitted for execution by the user.
Impact
An attacker who shares a notebook or a Markdown file - via email, GitHub, or a Binder link - can invoke an arbitrary command upon a single click by the victim. The button can be rendered inside the output area and be visually indistinguishable from a legitimate widget. No kernel needs to start; the HTML output is stored in the notebook file and displayed immediately on open.
Single-click impact
An attacker convincing the victim to click on a single button or link can:
- execute arbitrary code in the available kernels,
- delete files leading to information loss; in principle the loss could be unrecoverable, depending on server configuration and attack complexity,
- open multiple kernels/terminals at once, or create multiple files at once, putting significant stress on the server and thus deny availability for other users when using standalone multi-tenant jupyter-server deployment, and to a lesser degree impact availability on JupyterHub deployments.
The arbitrary code execution will be immediately visible to the user; and can be halted by the timely user intervention. The deletion of files can be silent and go unnoticed for some time.
Multi-click attacks
An attacker who convinces the victim to click on multiple buttons in specific order and to grant access to clipboard (or in scenarios where the user already granted keyboard access) can obtain full access to the terminal and execute arbitrary commands in the environment with access scope that might exceed that of available kernels. Only users of Chromium-based browsers are susceptible to this expanded variant of the attack.
The execution of commands in the terminal would be immediately visible to the user.
Impact of third-party extensions
The impact described above assumes a plain JupyterLab/Notebook installation. In environments with frontend extensions that contribute additional commands the attack surface is increased by the functionality covered by these commands.
Patches
JupyterLab 4.5.7
Workarounds
No workarounds are available for end-users.
Downstream applications inheriting from JupyterFrontEnd or JupyterLab can effectively disable the CommandLinker by passing commandLinker: new CommandLinker({ commands: new CommandRegistry() }) option in the initialization options.
Hardening
The patched versions include a toggle to disable the command linker functionality altogether, for example via overrides.json:
{
"@jupyterlab/apputils-extension:sanitizer": {
"allowCommandLinker": false
}
}
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | jupyterlab | all versions | 4.5.7 |
| 🐍PyPI | notebook | ≥ 7.0.0&&< 7.5.6 | 7.5.6 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jupyterlab. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update jupyterlab to 4.5.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mqcg-5x36-vfcg is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-mqcg-5x36-vfcg is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-mqcg-5x36-vfcg. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mqcg-5x36-vfcg in your dependencies?
O3 detects GHSA-mqcg-5x36-vfcg across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.