Blocked request. This host ("app") is not allowed.

[MariuzM]

Describe the bug

I updated Vite to latest now I'm starting to have this, then i downgraded but still same thing, what is happening?

Blocked request. This host ("app") is not allowed.
To allow this host, add "app" to preview.allowedHosts in vite.config.js.

I use Railway as hosting and i have no idea how to fix this?

Reproduction

https://github.com/MariuzM/frameworks/tree/main/react-tsr

Steps to reproduce

No response

System Info

System:
    OS: macOS 14.7.2
    CPU: (10) arm64 Apple M1 Max
    Memory: 24.44 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.17.0 - ~/dev/node-v20.17.0/bin/node
    Yarn: 1.22.22 - ~/dev/node-v20.17.0/bin/yarn
    npm: 10.8.2 - ~/dev/node-v20.17.0/bin/npm
    pnpm: 9.12.2 - ~/Library/pnpm/pnpm
    bun: 1.2.2 - ~/.bun/bin/bun
  Browsers:
    Brave Browser: 133.1.75.175
    Chrome: 130.0.6723.70
    Safari: 18.2

Used Package Manager

bun

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

Since Vite 6.0.9+, 5.4.12+, 4.5.6+, you need to set preview.allowedHost if you are accessing the server with a host name other than localhost.
See GHSA-vg6x-rcgg-rjx6 for more details.