diff --git a/Changes b/Changes
index 254eb7ff..81481927 100644
--- a/Changes
+++ b/Changes
@@ -1,6 +1,13 @@
 Revision history for WWW::Mechanize
 
 {{$NEXT}}
+    [FIXED]
+    - Credential headers set via add_header() (Authorization,
+      Proxy-Authorization and Cookie) are no longer re-applied to cross-origin
+      redirect targets, so they are not disclosed to a different origin. This
+      matches LWP::UserAgent's own redirect handling; set
+      allow_credentialed_redirects to a true value to opt out. (GH#433) (Olaf
+      Alders)
 
 2.22      2026-06-18 20:59:34Z
     [ENHANCEMENTS]
diff --git a/lib/WWW/Mechanize.pm b/lib/WWW/Mechanize.pm
index 9dfd7a47..1a40e945 100644
--- a/lib/WWW/Mechanize.pm
+++ b/lib/WWW/Mechanize.pm
@@ -149,6 +149,7 @@ use Tie::RefHash       ();
 use HTTP::Request 1.30 ();
 use HTML::Form 1.00    ();
 use HTML::TokeParser   ();
+use Scalar::Util       qw( blessed );
 
 use parent 'LWP::UserAgent';
 
@@ -291,6 +292,12 @@ sub new {
         strict_forms    => 0,          # pass-through to HTML::Form
         verbose_forms   => 0,          # pass-through to HTML::Form
         marked_sections => 1,
+
+        # Owned by Mech so the cross-origin credential strip honours it on
+        # every LWP version. We store it in the same hash slot LWP::UserAgent
+        # uses, so LWP's own strip (6.83+) reads it too, and we keep it out of
+        # the parent constructor, which would carp on it under older LWP.
+        allow_credentialed_redirects => 0,
     );
 
     my %passed_params = @_;
@@ -3068,7 +3075,11 @@ sub request {
     $self->die('->request was called without a request parameter')
         unless $request;
 
-    $request = $self->_modify_request($request);
+    # On a redirect or auth retry, LWP::UserAgent re-enters request() and
+    # threads the triggering response through as the fourth positional
+    # argument ( $request, $arg, $size, $response ). _modify_request() uses
+    # it to detect a cross-origin hop. @_ now holds ( $arg, $size, $response ).
+    $request = $self->_modify_request( $request, $_[2] );
 
     if ( $request->method eq 'GET' || $request->method eq 'POST' ) {
         $self->_push_page_stack();
@@ -3288,9 +3299,13 @@ L<Compress::Zlib> is installed.
 
 =cut
 
+my %CREDENTIAL_HEADER
+    = map { $_ => 1 } qw( authorization proxy-authorization cookie );
+
 sub _modify_request {
-    my $self = shift;
-    my $req  = shift;
+    my $self     = shift;
+    my $req      = shift;
+    my $previous = shift;
 
     # add correct Accept-Encoding header to restore compliance with
     # http://www.freesoft.org/CIE/RFC/2068/158.htm
@@ -3306,6 +3321,18 @@ sub _modify_request {
         $last = $last->as_string if ref($last);
         $req->header( Referer => $last );
     }
+
+    # Detect a cross-origin redirect hop. LWP::UserAgent threads the triggering
+    # response in as $previous when it re-enters request() to follow a redirect;
+    # $previous->request->uri is the origin we are coming from.
+    my $strip_credentials
+        = $previous
+        && blessed($previous)
+        && $previous->can('request')
+        && $previous->request
+        && !$self->{allow_credentialed_redirects}
+        && $self->_is_cross_origin( $previous->request->uri, $req->uri );
+
     while ( my ( $key, $value ) = each %{ $self->{headers} } ) {
         if ( defined $value ) {
             $req->header( $key => $value );
@@ -3315,9 +3342,36 @@ sub _modify_request {
         }
     }
 
+    # On a cross-origin redirect, credential headers must not be disclosed to
+    # the new origin (the CVE-2018-1000007 class of leak). Remove them here so
+    # neither our own persistent add_header() values (re-applied just above)
+    # nor headers carried forward by LWP survive the hop. Recent LWP strips
+    # these from the redirected request itself, but older releases clone them
+    # forward, so we cannot rely on that. allow_credentialed_redirects opts out.
+    if ($strip_credentials) {
+        $req->remove_header( keys %CREDENTIAL_HEADER );
+    }
+
     return $req;
 }
 
+# Mirror the scheme/host/port comparison LWP::UserAgent uses when deciding
+# whether a redirect crosses origins (see LWP::UserAgent::request).
+sub _is_cross_origin {
+    my ( $self, $from, $to ) = @_;
+
+    # Both URIs are absolute request URIs (LWP rejects relative URLs before
+    # they get here), so scheme is always defined. canonical() lower-cases the
+    # scheme and host, so a case-only difference does not count as cross-origin,
+    # and host_port supplies the scheme's default port when none is given, so
+    # http://h/ and http://h:80/ compare equal.
+    $from = $from->canonical;
+    $to   = $to->canonical;
+
+    return $from->scheme ne $to->scheme
+        || $from->host_port ne $to->host_port;
+}
+
 =head2 $mech->_make_request()
 
 Convenience method to make it easier for subclasses like L<WWW::Mechanize::Cached> to intercept the
diff --git a/t/cross-origin-redirect.t b/t/cross-origin-redirect.t
new file mode 100644
index 00000000..501b2cff
--- /dev/null
+++ b/t/cross-origin-redirect.t
@@ -0,0 +1,183 @@
+use strict;
+use warnings;
+
+use Test::More;
+use HTTP::Response ();
+
+# A persistent header set via add_header() must not be re-applied to a
+# cross-origin redirect target. LWP strips Authorization/Proxy-Authorization
+# on cross-origin redirects (the CVE-2018-1000007 mitigation); Mech must not
+# put them back via its _modify_request() header loop.
+#
+# Transport is mocked so LWP's *real* redirect loop runs; only the socket
+# layer is replaced. Each request the agent emits is recorded so we can
+# inspect the header that reached the redirect target.
+
+{
+    package TestMech;
+    use parent 'WWW::Mechanize';
+
+    sub simple_request {
+        my ( $self, $req ) = @_;
+        push @{ $self->{_seen} }, $req;
+
+        my $location = $self->{_route}{ $req->uri->as_string };
+        if ($location) {
+            my $r = HTTP::Response->new( $self->{_status} || 302 );
+            $r->header( Location => $location );
+            $r->request($req);
+            return $r;
+        }
+        my $r = HTTP::Response->new(
+            200,                             'OK',
+            [ 'Content-Type', 'text/html' ], 'ok'
+        );
+        $r->request($req);
+        return $r;
+    }
+}
+
+my @cases = (
+    {
+        name     => 'cross-origin redirect strips persistent Authorization',
+        header   => 'Authorization',
+        value    => 'Basic SECRET',
+        start    => 'http://hosta.example/',
+        location => 'http://hostb.example/',
+        opts     => {},
+        expect   => undef,
+    },
+    {
+        name => 'cross-origin redirect strips persistent Proxy-Authorization',
+        header   => 'Proxy-Authorization',
+        value    => 'Basic SECRET',
+        start    => 'http://hosta.example/',
+        location => 'http://hostb.example/',
+        opts     => {},
+        expect   => undef,
+    },
+    {
+        name     => 'same-origin redirect preserves persistent Authorization',
+        header   => 'Authorization',
+        value    => 'Basic SECRET',
+        start    => 'http://hosta.example/one',
+        location => 'http://hosta.example/two',
+        opts     => {},
+        expect   => 'Basic SECRET',
+    },
+    {
+        name =>
+            'cross-origin to different port strips persistent Authorization',
+        header   => 'Authorization',
+        value    => 'Basic SECRET',
+        start    => 'http://hosta.example/',
+        location => 'http://hosta.example:8080/',
+        opts     => {},
+        expect   => undef,
+    },
+    {
+        name =>
+            'case-only host difference is same-origin and preserves header',
+        header   => 'Authorization',
+        value    => 'Basic SECRET',
+        start    => 'http://hosta.example/',
+        location => 'http://HOSTA.example/',
+        opts     => {},
+        expect   => 'Basic SECRET',
+    },
+    {
+        name     => 'cross-origin redirect strips persistent Cookie',
+        header   => 'Cookie',
+        value    => 'session=SECRET',
+        start    => 'http://hosta.example/',
+        location => 'http://hostb.example/',
+        opts     => {},
+        expect   => undef,
+    },
+    {
+        name     => 'same-origin redirect preserves persistent Cookie',
+        header   => 'Cookie',
+        value    => 'session=SECRET',
+        start    => 'http://hosta.example/one',
+        location => 'http://hosta.example/two',
+        opts     => {},
+        expect   => 'session=SECRET',
+    },
+    {
+        name   => 'allow_credentialed_redirects opts back in to cross-origin',
+        header => 'Authorization',
+        value  => 'Basic SECRET',
+        start  => 'http://hosta.example/',
+        location => 'http://hostb.example/',
+        opts     => { allow_credentialed_redirects => 1 },
+        expect   => 'Basic SECRET',
+    },
+    {
+        name   => 'scheme change (http to https) is cross-origin and strips',
+        header => 'Authorization',
+        value  => 'Basic SECRET',
+        start  => 'http://hosta.example/',
+        location => 'https://hosta.example/',
+        opts     => {},
+        expect   => undef,
+    },
+    {
+        name   => '307 redirect strips persistent Authorization cross-origin',
+        header => 'Authorization',
+        value  => 'Basic SECRET',
+        start  => 'http://hosta.example/',
+        location => 'http://hostb.example/',
+        status   => 307,
+        opts     => {},
+        expect   => undef,
+    },
+    {
+        # Same-origin hop preserves the header, then a cross-origin hop strips
+        # it: the verdict is made per hop, so a later same-origin target does
+        # not get the credential back once an intervening hop has dropped it.
+        name   => 'multi-hop redirect strips at the cross-origin hop',
+        header => 'Authorization',
+        value  => 'Basic SECRET',
+        start  => 'http://hosta.example/one',
+        route  => {
+            'http://hosta.example/one' => 'http://hosta.example/two',
+            'http://hosta.example/two' => 'http://hostb.example/',
+        },
+        final  => 'http://hostb.example/',
+        opts   => {},
+        expect => undef,
+    },
+);
+
+for my $case (@cases) {
+    subtest $case->{name} => sub {
+        my $mech = TestMech->new( autocheck => 0, %{ $case->{opts} } );
+        $mech->{_route}
+            = $case->{route} || { $case->{start} => $case->{location} };
+        $mech->{_status} = $case->{status};
+        $mech->add_header( $case->{header} => $case->{value} );
+
+        $mech->get( $case->{start} );
+
+        my @seen = @{ $mech->{_seen} };
+        is(
+            $seen[0]->header( $case->{header} ),
+            $case->{value},
+            'first request carries the persistent header',
+        );
+
+        my $final = $seen[-1];
+        is(
+            $final->uri->as_string,
+            $case->{final} || $case->{location},
+            'final request reached the redirect target',
+        );
+        is(
+            scalar $final->header( $case->{header} ),
+            $case->{expect},
+            'header on the redirect target is as expected',
+        );
+    };
+}
+
+done_testing;