diff --git a/webrtc/p2p/base/turnport.cc b/webrtc/p2p/base/turnport.cc
index 2d5e30e663..a34d25b612 100644
--- a/webrtc/p2p/base/turnport.cc
+++ b/webrtc/p2p/base/turnport.cc
@@ -639,6 +639,14 @@ bool TurnPort::SetAlternateServer(const rtc::SocketAddress& address) {
     return false;
   }
 
+  // Block redirects to a loopback address.
+  // See: https://bugs.chromium.org/p/chromium/issues/detail?id=649118
+  if (address.IsLoopbackIP()) {
+    LOG_J(LS_WARNING, this)
+        << "Blocking attempted redirect to loopback address.";
+    return false;
+  }
+
   LOG_J(LS_INFO, this) << "Redirecting from TURN server ["
                        << server_address_.address.ToSensitiveString()
                        << "] to TURN server ["
diff --git a/webrtc/p2p/base/turnport_unittest.cc b/webrtc/p2p/base/turnport_unittest.cc
index edb345447b..a8153eed26 100644
--- a/webrtc/p2p/base/turnport_unittest.cc
+++ b/webrtc/p2p/base/turnport_unittest.cc
@@ -29,6 +29,7 @@
 #include "webrtc/base/helpers.h"
 #include "webrtc/base/logging.h"
 #include "webrtc/base/physicalsocketserver.h"
+#include "webrtc/base/socketadapters.h"
 #include "webrtc/base/socketaddress.h"
 #include "webrtc/base/ssladapter.h"
 #include "webrtc/base/thread.h"
@@ -441,6 +442,57 @@ class TurnPortTest : public testing::Test,
     ASSERT_EQ(0U, turn_port_->Candidates().size());
   }
 
+  // A certain security exploit works by redirecting to a loopback address,
+  // which doesn't ever actually make sense. So redirects to loopback should
+  // be treated as errors.
+  // See: https://bugs.chromium.org/p/chromium/issues/detail?id=649118
+  void TestTurnAlternateServerLoopback(ProtocolType protocol_type, bool ipv6) {
+    const SocketAddress& local_address = ipv6 ? kLocalIPv6Addr : kLocalAddr1;
+    const SocketAddress& server_address =
+        ipv6 ? kTurnIPv6IntAddr : kTurnIntAddr;
+
+    std::vector<rtc::SocketAddress> redirect_addresses;
+    SocketAddress loopback_address(ipv6 ? "::1" : "127.0.0.1",
+                                   TURN_SERVER_PORT);
+    redirect_addresses.push_back(loopback_address);
+
+    // Make a socket and bind it to the local port, to make extra sure no
+    // packet is sent to this address.
+    std::unique_ptr<rtc::Socket> loopback_socket(ss_->CreateSocket(
+        protocol_type == PROTO_UDP ? SOCK_DGRAM : SOCK_STREAM));
+    ASSERT_NE(nullptr, loopback_socket.get());
+    ASSERT_EQ(0, loopback_socket->Bind(loopback_address));
+    if (protocol_type == PROTO_TCP) {
+      ASSERT_EQ(0, loopback_socket->Listen(1));
+    }
+
+    TestTurnRedirector redirector(redirect_addresses);
+
+    turn_server_.AddInternalSocket(server_address, protocol_type);
+    turn_server_.set_redirect_hook(&redirector);
+    CreateTurnPort(local_address, kTurnUsername, kTurnPassword,
+                   ProtocolAddress(server_address, protocol_type));
+
+    turn_port_->PrepareAddress();
+    EXPECT_TRUE_SIMULATED_WAIT(
+        turn_error_,
+        (protocol_type == PROTO_TCP ? kSimulatedRtt * 3 : kSimulatedRtt * 2),
+        fake_clock_);
+
+    // Wait for some extra time, and make sure no packets were received on the
+    // loopback port we created (or in the case of TCP, no connection attempt
+    // occurred).
+    SIMULATED_WAIT(false, kSimulatedRtt, fake_clock_);
+    if (protocol_type == PROTO_UDP) {
+      char buf[1];
+      EXPECT_EQ(-1, loopback_socket->Recv(&buf, 1, nullptr));
+    } else {
+      std::unique_ptr<rtc::Socket> accepted_socket(
+          loopback_socket->Accept(nullptr));
+      EXPECT_EQ(nullptr, accepted_socket.get());
+    }
+  }
+
   void TestTurnConnection(ProtocolType protocol_type) {
     // Create ports and prepare addresses.
     PrepareTurnAndUdpPorts(protocol_type);
@@ -917,6 +969,23 @@ TEST_F(TurnPortTest, TestTurnAlternateServerDetectRepetitionTCP) {
   TestTurnAlternateServerDetectRepetition(PROTO_TCP);
 }
 
+// Test catching the case of a redirect to loopback.
+TEST_F(TurnPortTest, TestTurnAlternateServerLoopbackUdpIpv4) {
+  TestTurnAlternateServerLoopback(PROTO_UDP, false);
+}
+
+TEST_F(TurnPortTest, TestTurnAlternateServerLoopbackUdpIpv6) {
+  TestTurnAlternateServerLoopback(PROTO_UDP, true);
+}
+
+TEST_F(TurnPortTest, TestTurnAlternateServerLoopbackTcpIpv4) {
+  TestTurnAlternateServerLoopback(PROTO_TCP, false);
+}
+
+TEST_F(TurnPortTest, TestTurnAlternateServerLoopbackTcpIpv6) {
+  TestTurnAlternateServerLoopback(PROTO_TCP, true);
+}
+
 // Do a TURN allocation and try to send a packet to it from the outside.
 // The packet should be dropped. Then, try to send a packet from TURN to the
 // outside. It should reach its destination. Finally, try again from the