Yes, if you drop user input into it raw. This is the same family as front-end script injection, just on the server side - and it is easy to miss because most XSS advice is aimed at frontends.
The shape. Your backend turns user input into a web page and serves it back: a report, a chart page, an analysis tearsheet. Whatever the user typed - a stock symbol, a label, a name - gets printed inside that page. Put it in raw, and a visitor can supply a value that is not really a label but a hidden instruction, which the browser then runs as code on your web address. That smuggled code can read the visitor's login session, change what the page shows, or send them to a fake login screen. The risk is any user value that lands inside HTML you hand back.
Two cheap defenses, used together. First, escape the user's text before placing it in the page, so characters like < and > become harmless symbols instead of the start of a tag (in Python, html.escape()). Second, attach two response headers that tell the browser to be strict: a Content-Security-Policy (which sources of scripts, styles and images may even run) and X-Content-Type-Options: nosniff (do not guess a file is something other than what you said). Together they mean that even if a bad value slips past the escaping, the browser refuses to run the injected script.
The coverage gap to watch: apply those headers to every report page your backend serves - both files served out of a /static folder and any HTML you return directly. It is easy to add the middleware and still leave the static path bare.
Full item with the middleware: https://www.tigzig.com/security/backend.
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