fix(http): normalize the host before the private network check

parse_url() keeps the brackets around an IPv6 literal, so "[::1]" or
"[::ffff:127.0.0.1]" never matched an address and isPrivateURL() let the
request through. A host that does not resolve was allowed for the same
reason, while cURL still connects to forms like "0x7f000001" or
"127.0.0.1." on its own.

Strip the brackets and the trailing dot, check IP literals directly, check
every resolved address, and treat a host without any address as private.
IPv4-mapped IPv6 addresses are checked through their IPv4 part, since
FILTER_FLAG_NO_RES_RANGE does not classify them the same way on every PHP
version.

Fixes #5858
Fixes #5871

app/Core/Http/Client.php

@@ -401,6 +401,12 @@ class Client extends Base
             return false;
         }
 
+        // IPv4-mapped IPv6 address (::ffff:a.b.c.d), check the IPv4 part
+        $address = inet_pton($ip);
+        if (strlen($address) === 16 && substr($address, 0, 12) === str_repeat("\0", 10)."\xff\xff") {
+            $ip = inet_ntop(substr($address, 12));
+        }
+
         return filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) === false;
     }
 
@@ -423,29 +429,40 @@ class Client extends Base
             return false;
         }
 
-        $host = trim($parsedUrl['host']);
+        $host = rtrim(trim($parsedUrl['host'], " \t\n\r\0\x0B[]"), '.');
         if ($host === '') {
             return false;
         }
 
-        $ipv4Address = gethostbyname($host);
-        if ($this->isPrivateIpAddress($ipv4Address)) {
-            return true;
+        if (filter_var($host, FILTER_VALIDATE_IP) !== false) {
+            return $this->isPrivateIpAddress($host);
         }
 
+        $addresses = gethostbynamel($host) ?: [];
+
         if (function_exists('dns_get_record')) {
             $dnsRecords = @dns_get_record($host, DNS_AAAA);
             if (is_array($dnsRecords)) {
                 foreach ($dnsRecords as $record) {
                     if (isset($record['type']) && $record['type'] === 'AAAA' && isset($record['ipv6'])) {
-                        if ($this->isPrivateIpAddress($record['ipv6'])) {
-                            return true;
-                        }
+                        $addresses[] = $record['ipv6'];
                     }
                 }
             }
         }
 
+        // Refuse hosts we cannot resolve: the HTTP client may still connect to them,
+        // for example cURL reads "0x7f000001" as 127.0.0.1.
+        if (empty($addresses)) {
+            return true;
+        }
+
+        foreach ($addresses as $address) {
+            if ($this->isPrivateIpAddress($address)) {
+                return true;
+            }
+        }
+
         return false;
     }
 }

tests/units/Core/Http/ClientTest.php

@@ -45,6 +45,17 @@ class ClientTest extends Base
         $this->assertTrue($client->isPrivateIpAddress('fd12:3456:789a:1::1'));
     }
 
+    public function testIsPrivateIpAddressWithIPv4MappedIPv6()
+    {
+        $client = new Client($this->container);
+
+        $this->assertTrue($client->isPrivateIpAddress('::ffff:127.0.0.1'));
+        $this->assertTrue($client->isPrivateIpAddress('::ffff:7f00:1'));
+        $this->assertTrue($client->isPrivateIpAddress('::ffff:169.254.169.254'));
+        $this->assertTrue($client->isPrivateIpAddress('::ffff:10.0.0.1'));
+        $this->assertFalse($client->isPrivateIpAddress('::ffff:8.8.8.8'));
+    }
+
     public function testIsPrivateIpAddressWithPublicAndInvalidValues()
     {
         $client = new Client($this->container);
@@ -64,6 +75,36 @@ class ClientTest extends Base
         $this->assertTrue($client->isPrivateURL('http://10.0.0.15/api'));
     }
 
+    public function testIsPrivateUrlWithBracketedIPv6Literals()
+    {
+        $client = new Client($this->container);
+
+        $this->assertTrue($client->isPrivateURL('http://[::1]/'));
+        $this->assertTrue($client->isPrivateURL('http://[::ffff:127.0.0.1]:9099/'));
+        $this->assertTrue($client->isPrivateURL('http://[0:0:0:0:0:ffff:127.0.0.1]/'));
+        $this->assertTrue($client->isPrivateURL('http://[::ffff:169.254.169.254]/'));
+        $this->assertTrue($client->isPrivateURL('http://[fd00::1]/'));
+        $this->assertFalse($client->isPrivateURL('http://[2607:f8b0:4005:805::200e]/'));
+    }
+
+    public function testIsPrivateUrlWithOtherIPv4Notations()
+    {
+        $client = new Client($this->container);
+
+        $this->assertTrue($client->isPrivateURL('http://2130706433:9000/'));
+        $this->assertTrue($client->isPrivateURL('http://0x7f000001/'));
+        $this->assertTrue($client->isPrivateURL('http://0177.0.0.1/'));
+        $this->assertTrue($client->isPrivateURL('http://2852039166/'));
+        $this->assertTrue($client->isPrivateURL('http://127.0.0.1./'));
+    }
+
+    public function testIsPrivateUrlWithUnresolvableHost()
+    {
+        $client = new Client($this->container);
+
+        $this->assertTrue($client->isPrivateURL('http://kanboard.invalid/'));
+    }
+
     public function testIsPrivateUrlWithPublicAddresses()
     {
         $client = new Client($this->container);