Mojolicious::Plugin::Web::Auth::OAuth2 versions through 0.17 for Perl have an insecure default state parameter.
When no state generator is specified in the constructor, the module defaults to using a SHA-1 hash of predictable and low-entropy sources, including the epoch time (which is leaked via the HTTP Date header) and a call to Perl's built-in rand function.
A predictable state allows an attacker to hijack another user's session through cross site request forgery (CSRF).
Users should specify a state_generator function in the plugin configuration that uses a secure CSPRNG such as Crypt::PRNG or (for Mojolicious 9.46 or later) the Mojo::Util::random_bytes function. For example,
plugin 'Web::Auth',
module => 'OAuth2',
...
state_generator => sub {
unpack("H*", Mojo::Util::random_bytes(20))
};