Open redirect in Phoenix.LiveView.validate_local_url!/2 via ASCII tab, LF and CR
Summary
URL Redirection to Untrusted Site ('Open Redirect') vulnerability in phoenixframework phoenix\_live\_view allows an attacker to send a victim's browser to an origin of the attacker's choosing via a :to value containing ASCII tab, LF or CR.
redirect/2 validates :to through the private validate\_local\_url!/2 in lib/phoenix\_live\_view.ex, which is intended to guarantee the target is a path within the application. It rejects a leading // and any backslash, but not ASCII tab, LF or CR. Browsers strip those three characters before parsing a URL, so a value such as /<TAB>/example.com passes validation as a path and is then resolved as the scheme-relative URL //example.com. The live navigation functions share the guard but are not affected, because the client expands their target against the current origin. push\_patch/2 is also affected before 0.7.0, which is when that expansion was added.
This issue affects phoenix\_live\_view: from 0.5.0 before 1.0.19, from 1.1.0-rc.0 before 1.1.33, and from 1.2.0-rc.0 before 1.2.9.
Workaround
Reject any untrusted value containing ASCII tab, LF or CR before passing it as :to to redirect/2, or to push\_patch/2 before 0.7.0. Alternatively, map client-supplied navigation targets to a fixed set of known-good paths rather than forwarding the value.
Configuration
The application must pass an externally influenced value as :to to redirect/2, or to push\_patch/2 before 0.7.0, for example a return\_to parameter carried through sign-in or a navigation target taken from a handle\_event/3 payload.
