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MNT: Restrict webagg toolbar actions to valid actions - #31294
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March 13, 2026 00:59
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lib/matplotlib/backends/backend_webagg.py
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I'm 👍🏻 on the toolbar change, but confused by the CORS change as I think tornando defaults to locked down. |
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lib/matplotlib/backends/backend_webagg_core.py
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lib/matplotlib/tests/test_backend_webagg.py
Co-authored-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>
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PR summary
The WebAgg backend starts a local Tornado web server with no origin checking on its WebSocket handler and an open getattr dispatch for toolbar actions. This means any webpage a user visits while WebAgg is running can silently connect to the server, receive figure image data, and invoke arbitrary zero-argument methods on the toolbar object.
The good news is that I believe this is sandboxed to the figure window & its methods, and does not allows for arbitrary code execution. So the blast radius is pretty limited. @tacaswell FYI
This adds origin checking to the websocket handler, to ensure all requests are coming from the webagg server hosting the figure. And it restricts the toolbar button dispatch to only allow acting on the actual toolbar buttons.
AI Disclosure
Claude authored, manually reviewed.
PR checklist