FiftyOne App server uses wildcard CORS (Access-Control-Allow-Origin: *), enabling cross-origin reads of local server data

Impact

The FiftyOne App/API server (fiftyone/server/app.py) and the /media route (fiftyone/server/routes/media.py) unconditionally set a permissive CORS header (Access-Control-Allow-Origin: *) on their responses. Because the embedded App server runs locally and is unauthenticated, this allows any website a user visits to make cross-origin requests to that user's running FiftyOne server and read the responses.

Combined with the unauthenticated /media endpoint — which serves files from the local filesystem by path — the wildcard CORS policy turns a local-only file read into a remotely exploitable, drive-by data exfiltration vulnerability. A malicious web page can silently issue requests such as http://localhost:5151/media?filepath=/etc/passwd and read arbitrary files accessible to the server process (SSH keys, cloud credentials, .env files, dataset media, etc.), then exfiltrate them to an attacker-controlled endpoint.

The victim only needs to have a FiftyOne server running locally and visit a malicious page — no clicks or other interaction are required. Browsers that have shipped Private Network Access / local-network-access protections (e.g. Chromium 142+) mitigate this for some users, but Safari and Firefox do not yet, so the attack remains viable in common configurations.

Who is impacted: any user running FiftyOne (the open-source, embedded App server) locally while also browsing the web.

Not affected: media stored in cloud buckets, which is served via signed URLs on a separate origin.

Patches

Fixed in FiftyOne 1.17.0. The hard-coded Access-Control-Allow-Origin: * has been removed and the server now responds same-origin only by default, which covers local desktop usage and the supported notebook integrations (each served through a same-origin proxy or iframe).

Cross-origin access is now opt-in via a new allowed_origins config option (environment variable FIFTYONE_ALLOWED_ORIGINS), an explicit comma-separated list of trusted origins, e.g.:

export FIFTYONE_ALLOWED_ORIGINS='https://app.example.com,http://localhost:3000'

The literal value * restores the legacy wildcard behavior for users who explicitly require it and emits a warning.

Users should upgrade to FiftyOne 1.17.0 or later.

Workarounds

In affected versions there is no configuration flag to disable the wildcard CORS header without upgrading. Until you can upgrade:

• Do not run the FiftyOne App server while browsing untrusted websites.
• Keep the App server bound to localhost (the default) and avoid exposing it on a network interface.
• Use a browser that enforces Private Network Access protections.

Resources

• OWASP A01:2025 – Broken Access Control: https://owasp.org/Top10/2025/A01_2025-Broken_Access_Control/