PYSEC-2026-1691

### Summary

On Windows, converting a notebook containing SVG output to a PDF results in unauthorized code execution. Specifically, a third party can create a `inkscape.bat` file that defines a [Windows batch script](https://en.wikipedia.org/wiki/Batch_file), capable of arbitrary code execution.

When a user runs `jupyter nbconvert --to pdf` on a notebook containing SVG output to a PDF on a Windows platform from this directory, the `inkscape.bat` file is run unexpectedly.

### Details _Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer._

`nbconvert` searches for an `inkscape` executable when converting notebooks to PDFs here: https://github.com/jupyter/nbconvert/blob/4f61702f5c7524d8a3c4ac0d5fc33a6ac2fa36a7/nbconvert/preprocessors/svg2pdf.py#L104

The MITRE page on [CWE-427 (Uncontrolled Search Path Element)](https://cwe.mitre.org/data/definitions/427.html) summarizes the root cause succinctly:

> In Windows-based systems, when the `LoadLibrary` or `LoadLibraryEx` function is called with a DLL name that does not contain a fully qualified path, the function follows a search order that includes two path elements that might be uncontrolled: > - the directory from which the program has been loaded > - the current working directory

### PoC

_Complete instructions, including specific configuration details, to reproduce the vulnerability._

1. Create a directory containing:

- A hidden bat file called `inkscape.bat` containing `msg * "You've been hacked!"`

- A dummy ipynb file called `Machine_Learning.ipynb`

2. Run the command `jupyter nbconvert --to pdf Machine_Learning.ipynb`.

3. Wait a few seconds, and you should see a popup showing the message "You've been hacked!"

### Impact

All Windows users.