CVE-2026-27167

Gradio is an open-source Python package designed for quick prototyping. Starting in version 4.16.0 and prior to version 6.6.0, Gradio applications running outside of Hugging Face Spaces automatically enable "mocked" OAuth routes when OAuth components (e.g. `gr.LoginButton`) are used. When a user visits `/login/huggingface`, the server retrieves its own Hugging Face access token via `huggingface_hub.get_token()` and stores it in the visitor's session cookie. If the application is network-accessible, any remote attacker can trigger this flow to steal the server owner's HF token. The session cookie is signed with a hardcoded secret derived from the string `"-v4"`, making the payload trivially decodable. Version 6.6.0 fixes the issue.

Attacker scans for network-accessible Gradio instances (Shodan/Censys query on Gradio headers, port 7860). Identifies a target running v5.x with a gr.LoginButton in the UI — common in internal demo tools and ML team portals. Sends a single unauthenticated GET to /login/huggingface. Server automatically retrieves its own HF token via huggingface_hub.get_token() and stuffs it into a signed session cookie. Attacker reads the cookie, decodes it using the publicly known hardcoded '-v4' derived secret (no brute force needed — deterministic). Extracts the plaintext HF token. Uses token via HF API to enumerate private repos, download proprietary model weights, and push a poisoned model version with embedded backdoor. The org's downstream consumers pull the 'latest' tag and deploy the compromised model — full supply chain compromise from a single unauthenticated HTTP request.