aiohttp Cross-site Scripting vulnerability on index pages for static file handling

Summary

A XSS vulnerability exists on index pages for static file handling.

Details

When using web.static(..., show_index=True), the resulting index pages do not escape file names.

If users can upload files with arbitrary filenames to the static directory, the server is vulnerable to XSS attacks.

Workaround

We have always recommended using a reverse proxy server (e.g. nginx) for serving static files. Users following the recommendation are unaffected.

Other users can disable show_index if unable to upgrade.

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Patch: https://github.com/aio-libs/aiohttp/pull/8319/files