Electron: Use-after-free in download save dialog callback

### Impact Apps that allow downloads and programmatically destroy sessions may be vulnerable to a use-after-free. If a session is torn down while a native save-file dialog is open for a download, dismissing the dialog dereferences freed memory, which may lead to a crash or memory corruption. Apps that do not destroy sessions at runtime, or that do not permit downloads, are not affected. ### Workarounds Avoid destroying sessions while a download save dialog may be open. Cancel pending downloads before session teardown. ### Fixed Versions * `41.0.0-beta.7` * `40.7.0` * `39.8.0` * `38.8.6` ### For more information If there are any questions or comments about this advisory, please email [security@electronjs.org](mailto:security@electronjs.org)