Before validating a STUN packet, check it's big enough for a header.

webrtc/p2p/base/stun.cc

Index: webrtc/p2p/base/stun.cc
diff --git a/webrtc/p2p/base/stun.cc b/webrtc/p2p/base/stun.cc
index ac3fd5f9368bda2e7b2b042be87ee4db5e31b09f..180597ee77c11a46e52d379cf1c2fe5d7450291f 100644
--- a/webrtc/p2p/base/stun.cc
+++ b/webrtc/p2p/base/stun.cc
@@ -132,7 +132,7 @@ const StunUInt16ListAttribute* StunMessage::GetUnknownAttributes() const {
 bool StunMessage::ValidateMessageIntegrity(const char* data, size_t size,
                                            const std::string& password) {
   // Verifying the size of the message.
-  if ((size % 4) != 0) {
+  if ((size % 4) != 0 || size < kStunHeaderSize) {
     return false;
   }