♻️ Validate Server Sent Event fields to avoid applications from sending broken data#15588
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Merging this PR will not alter performance🎉 Hooray!
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Pull Request
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Description
♻️ Validate Server Sent Event fields to avoid applications from sending broken data
This was reported multiple times as a "vulnerability" by users probably using automated AI tools, with the argument that if input was taken from the request and passed directly to an event unfiltered, it could break the client.
If an app sets an
idoreventwith multi-line content, I would consider that app broken, and probably the app itself vulnerable to something, not FastAPI. With this change, if any app sets invalid multi-line values (sourced from unfiltered input or in any other way), FastAPI will make it a server error (which it is, as the app is sending invalid data).I don't think the code before this PR has a bug, less a vulnerability. This change is mainly a quality of life improvement to prevent badly written apps from shooting themselves in the foot by passing unsanitized data directly to a SSE.
AI Disclaimer
Codex with GPT-5.5
AI transcript
Checklist