diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,11 @@
+## 0.1.13
+
+- Garding the path_request attack.
+
+## 0.1.12
+
+- Fixing build.
+
 ## 0.1.11
 
 - Rescuing GHC 8.10, 9.0 and 9.2.
diff --git a/Network/QUIC/Connection/Migration.hs b/Network/QUIC/Connection/Migration.hs
--- a/Network/QUIC/Connection/Migration.hs
+++ b/Network/QUIC/Connection/Migration.hs
@@ -273,21 +273,21 @@
 validatePath :: Connection -> Maybe CIDInfo -> IO ()
 validatePath conn Nothing = do
     pdat <- newPathData
-    setChallenges conn [pdat]
+    setChallenges conn pdat
     putOutput conn $ OutControl RTT1Level [PathChallenge pdat] $ return ()
     waitResponse conn
 validatePath conn (Just (CIDInfo retiredSeqNum _ _)) = do
     pdat <- newPathData
-    setChallenges conn [pdat]
+    setChallenges conn pdat
     putOutput conn $
         OutControl RTT1Level [PathChallenge pdat, RetireConnectionID retiredSeqNum] $
             return ()
     waitResponse conn
     retirePeerCID conn retiredSeqNum
 
-setChallenges :: Connection -> [PathData] -> IO ()
-setChallenges Connection{..} pdats =
-    atomically $ writeTVar migrationState $ SendChallenge pdats
+setChallenges :: Connection -> PathData -> IO ()
+setChallenges Connection{..} pdat =
+    atomically $ writeTVar migrationState $ SendChallenge pdat
 
 setMigrationStarted :: Connection -> IO ()
 setMigrationStarted Connection{..} =
@@ -311,6 +311,6 @@
 checkResponse Connection{..} pdat = do
     state <- readTVarIO migrationState
     case state of
-        SendChallenge pdats
-            | pdat `elem` pdats -> atomically $ writeTVar migrationState RecvResponse
+        SendChallenge pdat'
+            | pdat == pdat' -> atomically $ writeTVar migrationState RecvResponse
         _ -> return ()
diff --git a/Network/QUIC/Connection/Misc.hs b/Network/QUIC/Connection/Misc.hs
--- a/Network/QUIC/Connection/Misc.hs
+++ b/Network/QUIC/Connection/Misc.hs
@@ -26,6 +26,7 @@
     readMinIdleTimeout,
     setMinIdleTimeout,
     sendFrames,
+    sendFrames1,
     closeConnection,
     abortConnection,
 ) where
@@ -174,6 +175,9 @@
 
 sendFrames :: Connection -> EncryptionLevel -> [Frame] -> IO ()
 sendFrames conn lvl frames = putOutput conn $ OutControl lvl frames $ return ()
+
+sendFrames1 :: Connection -> EncryptionLevel -> [Frame] -> IO ()
+sendFrames1 conn lvl frames = putOutput1 conn $ OutControl lvl frames $ return ()
 
 -- | Closing a connection with/without a transport error.
 --   Internal threads should use this.
diff --git a/Network/QUIC/Connection/Queue.hs b/Network/QUIC/Connection/Queue.hs
--- a/Network/QUIC/Connection/Queue.hs
+++ b/Network/QUIC/Connection/Queue.hs
@@ -3,6 +3,7 @@
 import UnliftIO.STM
 
 import Network.QUIC.Connection.Types
+import Network.QUIC.Imports
 import Network.QUIC.Stream
 import Network.QUIC.Types
 
@@ -29,6 +30,15 @@
 
 putOutput :: Connection -> Output -> IO ()
 putOutput conn out = atomically $ writeTQueue (outputQ conn) out
+
+putOutput1 :: Connection -> Output -> IO ()
+putOutput1 conn out = atomically $ do
+    ok <- isEmptyTBQueue (outputQ1 conn)
+    -- unless ok, the frames are intentionally dropped.
+    when ok $ writeTBQueue (outputQ1 conn) out
+
+takeOutput1STM :: Connection -> STM Output
+takeOutput1STM conn = readTBQueue (outputQ1 conn)
 
 ----------------------------------------------------------------
 
diff --git a/Network/QUIC/Connection/Types.hs b/Network/QUIC/Connection/Types.hs
--- a/Network/QUIC/Connection/Types.hs
+++ b/Network/QUIC/Connection/Types.hs
@@ -100,7 +100,7 @@
 data MigrationState
     = NonMigration
     | MigrationStarted
-    | SendChallenge [PathData]
+    | SendChallenge PathData
     | RecvResponse
     deriving (Eq, Show)
 
@@ -218,6 +218,7 @@
       inputQ :: InputQ
     , cryptoQ :: CryptoQ
     , outputQ :: OutputQ
+    , outputQ1 :: OutputQ1
     , migrationQ :: MigrationQ
     , shared :: Shared
     , delayedAckCount :: IORef Int
@@ -318,6 +319,7 @@
         <*> newTQueueIO
         <*> newTQueueIO
         <*> return outQ
+        <*> newTBQueueIO 1
         <*> newTQueueIO
         <*> newShared
         <*> newIORef 0
@@ -416,6 +418,7 @@
 type InputQ = TQueue Input
 type CryptoQ = TQueue Crypto
 type OutputQ = TQueue Output
+type OutputQ1 = TBQueue Output
 type MigrationQ = TQueue ReceivedPacket
 
 ----------------------------------------------------------------
diff --git a/Network/QUIC/Receiver.hs b/Network/QUIC/Receiver.hs
--- a/Network/QUIC/Receiver.hs
+++ b/Network/QUIC/Receiver.hs
@@ -381,7 +381,7 @@
                 unregister <- getUnregister conn
                 unregister cid
 processFrame conn RTT1Level (PathChallenge dat) =
-    sendFrames conn RTT1Level [PathResponse dat]
+    sendFrames1 conn RTT1Level [PathResponse dat]
 processFrame conn RTT1Level (PathResponse dat) =
     -- RTT0Level falls intentionally
     checkResponse conn dat
diff --git a/Network/QUIC/Sender.hs b/Network/QUIC/Sender.hs
--- a/Network/QUIC/Sender.hs
+++ b/Network/QUIC/Sender.hs
@@ -229,6 +229,7 @@
         atomically
             ( (SwPing <$> takePingSTM (connLDCC conn))
                 `orElse` (SwOut <$> takeOutputSTM conn)
+                `orElse` (SwOut <$> takeOutput1STM conn)
                 `orElse` (SwStrm <$> takeSendStreamQSTM conn)
             )
     case x of
diff --git a/Network/QUIC/Types/Frame.hs b/Network/QUIC/Types/Frame.hs
--- a/Network/QUIC/Types/Frame.hs
+++ b/Network/QUIC/Types/Frame.hs
@@ -107,7 +107,9 @@
 inFlight _                    = True
 
 rateControled :: Frame -> Bool
-rateControled ResetStream{} = True
-rateControled StopSending{} = True
-rateControled _             = False
+rateControled ResetStream{}   = True
+rateControled StopSending{}   = True
+rateControled PathChallenge{} = True
+rateControled PathResponse{}  = True
+rateControled _               = False
 {- FOURMOLU_ENABLE -}
diff --git a/quic.cabal b/quic.cabal
--- a/quic.cabal
+++ b/quic.cabal
@@ -1,6 +1,6 @@
 cabal-version:      >=1.10
 name:               quic
-version:            0.1.12
+version:            0.1.13
 license:            BSD3
 license-file:       LICENSE
 maintainer:         kazu@iij.ad.jp