PYSEC-2026-1477

## Impact

On Windows, the shared `%PROGRAMDATA%` directory is searched for configuration files (`SYSTEM_CONFIG_PATH` and `SYSTEM_JUPYTER_PATH`), which may allow users to create configuration files affecting other users.

Only shared Windows systems with multiple users and unprotected `%PROGRAMDATA%` are affected.

## Mitigations

- upgrade to `jupyter_core>=5.8.1` (5.8.0 is patched but breaks `jupyter-server`) , or - as administrator, modify the permissions on the `%PROGRAMDATA%` directory so it is not writable by unauthorized users, or - as administrator, create the `%PROGRAMDATA%\jupyter` directory with appropriately restrictive permissions, or - as user or administrator, set the `%PROGRAMDATA%` environment variable to a directory with appropriately restrictive permissions (e.g. controlled by administrators _or_ the current user)

## Credit

Reported via Trend Micro Zero Day Initiative as ZDI-CAN-25932