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python · Flask-SecurityHeads-up

Flask-Security Open Redirect via Backslash in URL Authority

Flask-Security's validate_redirect_url() function can be bypassed using a backslash in the URL authority, allowing open redirect when subdomain redirects are en

24 Jun 2026Read 1 minSeverity: schedule it

What changed

Flask-Security's validate_redirect_url() function can be bypassed using a backslash in the URL authority, allowing open redirect when subdomain redirects are enabled.

Who it affects

Applications using Flask-Security with SERVER_NAME and SECURITY_REDIRECT_ALLOW_SUBDOMAINS=True.

What to do today

Disable subdomain redirects or apply a fix that properly validates URLs with backslashes.

The trail
Collected Audited Written Published