CVE-2026-28415: 
Gradio vulnerability analysis and mitigation

CVE-2026-28415 is an open redirect vulnerability in Gradio's OAuth flow, classified as Moderate severity. The _redirect_to_target() function accepts an unvalidated _target_url query parameter, enabling redirection to arbitrary external URLs via the /logout and /login/callback endpoints. It affects all Gradio versions prior to 6.6.0 running on Hugging Face Spaces with OAuth enabled (i.e., using gr.LoginButton). Disclosed on February 27, 2026, it carries a CVSS v3.1 base score of 4.3 (Moderate) (GitHub Advisory, Gradio Security Advisory).

The root cause is CWE-601 (URL Redirection to Untrusted Site / Open Redirect), with contributing weaknesses CWE-200 and CWE-284. The vulnerable code in _redirect_to_target() directly passes the user-supplied _target_url query parameter to a RedirectResponse without any validation of the scheme or host:

def _redirect_to_target(request, default_target="/"):
    target = request.query_params.get("_target_url", default_target)
    return RedirectResponse(target)  # No validation

An attacker can craft a URL such as https://my-space.hf.space/logout?_target_url=https://evil.com/phishing, which, when visited by a user, redirects them to an attacker-controlled site. No authentication or special privileges are required to craft the malicious link; only user interaction (clicking the link) is needed (Gradio Security Advisory, GitHub Advisory).

The primary impact is phishing: attackers can leverage the trusted hf.space domain to redirect users to malicious external sites after logout or OAuth callback, increasing the likelihood that victims will trust and interact with the attacker-controlled page. This can result in credential theft or exposure of sensitive information entered on the phishing site. There is no direct server-side data exposure, code execution, or availability impact; the vulnerability is limited to integrity loss through user deception (Gradio Security Advisory, GitHub Advisory).

No public proof-of-concept exploit code has been identified, and there is no evidence of in-the-wild exploitation at this time (GitHub Advisory). The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.013% (2nd percentile), indicating a low probability of near-term exploitation. No threat actor attribution has been reported.

1. Identify target: Locate a Gradio application running on Hugging Face Spaces with OAuth enabled (i.e., using gr.LoginButton), running a version prior to 6.6.0.
2. Craft malicious URL: Construct a URL targeting the /logout or /login/callback endpoint with a malicious _target_url parameter, e.g., https://my-space.hf.space/logout?_target_url=https://evil.com/phishing.
3. Distribute the link: Send the crafted URL to target users via email, social media, or other channels. Because the URL originates from the trusted hf.space domain, users are more likely to trust it.
4. User interaction: When the victim clicks the link, the Gradio application processes the request and issues an HTTP redirect to the attacker-specified external URL without validation.
5. Phishing: The victim is redirected to the attacker-controlled site, where they may be prompted to enter credentials or other sensitive information (Gradio Security Advisory, GitHub Advisory).

• Network: HTTP requests to /logout or /login/callback endpoints containing a _target_url query parameter with an external scheme (e.g., http:// or https://) pointing to a non-hf.space domain; HTTP 302 redirect responses from Gradio apps pointing to external URLs.
• Logs: Web server or application access logs showing GET requests to /logout?_target_url=https://... or /login/callback?_target_url=https://... with external hostnames in the parameter value.
• User Reports: Users reporting unexpected redirects to unfamiliar external sites after logging out of or authenticating with a Gradio application on Hugging Face Spaces.

Upgrade Gradio to version 6.6.0 or later, which sanitizes the _target_url parameter to only use the path, query, and fragment components, stripping any scheme or host. No configuration-based workaround is available for unpatched versions; upgrading is the only remediation. Administrators should also review application logs for suspicious redirect activity on /logout and /login/callback endpoints, and educate users to verify URLs before entering credentials after authentication flows (Gradio Security Advisory, GitHub Advisory).

The vulnerability was reported by researcher logicx24 and published by Gradio maintainer freddyaboulton on February 27, 2026. Coverage has been limited to automated vulnerability tracking platforms and a small number of security blogs, reflecting the moderate severity and narrow scope of the issue (dev.to writeup, GitHub Advisory).