diff --git a/src/parser/__tests__/PhutilURITestCase.php b/src/parser/__tests__/PhutilURITestCase.php
index d002320..0253519 100644
--- a/src/parser/__tests__/PhutilURITestCase.php
+++ b/src/parser/__tests__/PhutilURITestCase.php
@@ -1,133 +1,159 @@
 <?php
 
 /**
  * Test cases for @{class:PhutilURI} parser.
  */
 final class PhutilURITestCase extends PhutilTestCase {
 
   public function testURIParsing() {
     $uri = new PhutilURI('http://user:pass@host:99/path/?query=value#fragment');
     $this->assertEqual('http', $uri->getProtocol(), 'protocol');
     $this->assertEqual('user', $uri->getUser(), 'user');
     $this->assertEqual('pass', $uri->getPass(), 'pass');
     $this->assertEqual('host', $uri->getDomain(), 'domain');
     $this->assertEqual('99', $uri->getPort(), 'port');
 
     $this->assertEqual('/path/', $uri->getPath(), 'path');
     $this->assertEqual(
       array(
         'query' => 'value',
       ),
       $uri->getQueryParams(),
       'query params');
     $this->assertEqual('fragment', $uri->getFragment(), 'fragment');
     $this->assertEqual(
       'http://user:pass@host:99/path/?query=value#fragment',
       (string)$uri,
       'uri');
 
 
     $uri = new PhutilURI('ssh://git@example.com/example/example.git');
     $this->assertEqual('ssh', $uri->getProtocol(), 'protocol');
     $this->assertEqual('git', $uri->getUser(), 'user');
     $this->assertEqual('', $uri->getPass(), 'pass');
     $this->assertEqual('example.com', $uri->getDomain(), 'domain');
     $this->assertEqual('', $uri->getPort(), 'port');
 
     $this->assertEqual('/example/example.git', $uri->getPath(), 'path');
     $this->assertEqual(array(), $uri->getQueryParams(), 'query params');
     $this->assertEqual('', $uri->getFragment(), 'fragment');
     $this->assertEqual(
       'ssh://git@example.com/example/example.git',
       (string)$uri,
       'uri');
 
 
     $uri = new PhutilURI('http://0@domain.com/');
     $this->assertEqual('0', $uri->getUser());
     $this->assertEqual('http://0@domain.com/', (string)$uri);
 
     $uri = new PhutilURI('http://0:0@domain.com/');
     $this->assertEqual('0', $uri->getUser());
     $this->assertEqual('0', $uri->getPass());
     $this->assertEqual('http://0:0@domain.com/', (string)$uri);
 
     $uri = new PhutilURI('http://%20:%20@domain.com/');
     $this->assertEqual(' ', $uri->getUser());
     $this->assertEqual(' ', $uri->getPass());
     $this->assertEqual('http://%20:%20@domain.com/', (string)$uri);
 
     $uri = new PhutilURI('http://%40:%40@domain.com/');
     $this->assertEqual('@', $uri->getUser());
     $this->assertEqual('@', $uri->getPass());
     $this->assertEqual('http://%40:%40@domain.com/', (string)$uri);
+
+    // These tests are covering cases where cURL and parse_url() behavior
+    // may differ in potentially dangerous ways. See T6755 for discussion.
+
+    // In general, we defuse these attacks by emitting URIs which escape
+    // special characters so that they are interpreted unambiguously by
+    // cURL in the same way that parse_url() interpreted them.
+
+    $uri = new PhutilURI('http://u:p@evil.com?@good.com');
+    $this->assertEqual('u', $uri->getUser());
+    $this->assertEqual('p', $uri->getPass());
+    $this->assertEqual('evil.com', $uri->getDomain());
+    $this->assertEqual('http://u:p@evil.com?%40good.com=', (string)$uri);
+
+    $uri = new PhutilURI('http://good.com#u:p@evil.com/');
+    $this->assertEqual('good.com#u', $uri->getUser());
+    $this->assertEqual('p', $uri->getPass());
+    $this->assertEqual('evil.com', $uri->getDomain());
+    $this->assertEqual('http://good.com%23u:p@evil.com/', (string)$uri);
+
+    $uri = new PhutilURI('http://good.com?u:p@evil.com/');
+    $this->assertEqual('', $uri->getUser());
+    $this->assertEqual('', $uri->getPass());
+    $this->assertEqual('good.com', $uri->getDomain());
+    $this->assertEqual('http://good.com?u%3Ap%40evil.com%2F=', (string)$uri);
+
   }
 
   public function testURIGeneration() {
     $uri = new PhutilURI('http://example.com');
     $uri->setPath('bar');
     $this->assertEqual('http://example.com/bar', $uri->__toString());
   }
 
   public function testStrictURIParsingOfHosts() {
     $uri = new PhutilURI('http://&amp;/');
     $this->assertEqual('', $uri->getDomain());
   }
 
   public function testStrictURIParsingOfLeadingWhitespace() {
     $uri = new PhutilURI(' http://example.com/');
     $this->assertEqual('', $uri->getDomain());
   }
 
   public function testAppendPath() {
     $uri = new PhutilURI('http://example.com');
     $uri->appendPath('foo');
     $this->assertEqual('http://example.com/foo', $uri->__toString());
     $uri->appendPath('bar');
     $this->assertEqual('http://example.com/foo/bar', $uri->__toString());
 
     $uri = new PhutilURI('http://example.com');
     $uri->appendPath('/foo/');
     $this->assertEqual('http://example.com/foo/', $uri->__toString());
     $uri->appendPath('/bar/');
     $this->assertEqual('http://example.com/foo/bar/', $uri->__toString());
 
     $uri = new PhutilURI('http://example.com');
     $uri->appendPath('foo');
     $this->assertEqual('http://example.com/foo', $uri->__toString());
     $uri->appendPath('/bar/');
     $this->assertEqual('http://example.com/foo/bar/', $uri->__toString());
   }
 
   public function testUnusualURIs() {
     $uri = new PhutilURI('file:///path/to/file');
     $this->assertEqual('file', $uri->getProtocol(), 'protocol');
     $this->assertEqual('', $uri->getDomain(), 'domain');
     $this->assertEqual('/path/to/file', $uri->getPath(), 'path');
 
     $uri = new PhutilURI('idea://open?x=/');
     $this->assertEqual('idea', $uri->getProtocol(), 'protocol');
     $this->assertEqual('open', $uri->getDomain(), 'domain');
     $this->assertEqual('', $uri->getPath(), 'path');
     $this->assertEqual(
       array(
         'x' => '/',
       ),
       $uri->getQueryParams());
   }
 
   public function testDefaultPorts() {
     $uri = new PhutilURI('http://www.example.com');
     $this->assertEqual('80', $uri->getPortWithProtocolDefault());
 
     $uri = new PhutilURI('https://www.example.com');
     $this->assertEqual('443', $uri->getPortWithProtocolDefault());
 
     $uri = new PhutilURI('ssh://git@example.com/example/example.git');
     $this->assertEqual('22', $uri->getPortWithProtocolDefault());
 
     $uri = new PhutilURI('unknown://www.example.com');
     $this->assertEqual('', $uri->getPortWithProtocolDefault());
   }
 
 }