Cross-check client-submitted fall time with server-measured time. When excessive difference is detected, punish player.

Fixes an exploit that could trivialize the Lich King encounter.

src/server/game/Entities/Player/Player.cpp

@@ -495,7 +495,7 @@ Player::Player(WorldSession* session): Unit(true)
 
     m_runes = nullptr;
 
-    m_lastFallTime = 0;
+    m_lastFallTimeClient = 0;
     m_lastFallZ = 0;
 
     m_grantableLevels = 0;
@@ -25453,7 +25453,25 @@ InventoryResult Player::CanEquipUniqueItem(ItemTemplate const* itemProto, uint8
 
 void Player::SetFallInformation(uint32 time, float z)
 {
-    m_lastFallTime = time;
+    if (time < m_lastFallTimeClient)
+        m_fallStartTimeServer = GameTime::GetGameTimeMS() - time;
+    else if (m_fallStartTimeServer && time < std::max<uint32>(GameTime::GetGameTimeMS() - m_fallStartTimeServer, 2500) - 2500)
+    {
+        TC_LOG_WARN("cheat", "Player %s found to be delaying their falling movement.", GetName().c_str());
+        switch (sWorld->getIntConfig(CONFIG_ANTICHEAT_FALL_PUNISHMENT))
+        {
+            case 1: // kill
+                EnvironmentalDamage(DAMAGE_FALL, GetMaxHealth());
+                if (!isDead())
+                    Kill(this, false);
+                break;
+            case 2: // disconnect
+                GetSession()->KickPlayer();
+                break;
+        }
+    }
+
+    m_lastFallTimeClient = time;
     m_lastFallZ = z;
 }
 
@@ -25461,6 +25479,22 @@ void Player::HandleFall(MovementInfo const& movementInfo)
 {
     // calculate total z distance of the fall
     float z_diff = m_lastFallZ - movementInfo.pos.GetPositionZ();
+    if (m_fallStartTimeServer && movementInfo.fallTime < std::max<uint32>(GameTime::GetGameTimeMS() - m_fallStartTimeServer, 2500) - 2500)
+    {
+        TC_LOG_WARN("cheat", "Player %s found to be delaying their falling movement.", GetName().c_str());
+        switch (sWorld->getIntConfig(CONFIG_ANTICHEAT_FALL_PUNISHMENT))
+        {
+            case 1: // kill
+                z_diff = MAX_HEIGHT;
+                break;
+            case 2: // disconnect
+                GetSession()->KickPlayer();
+                break;
+            default:
+                break;
+        }
+    }
+    m_fallStartTimeServer = 0;
     //TC_LOG_DEBUG("misc", "zDiff = %f", z_diff);
 
     //Players with low fall distance, Feather Fall or physical immunity (charges used) are ignored
@@ -25842,7 +25876,7 @@ void Player::AddKnownCurrency(uint32 itemId)
 
 void Player::UpdateFallInformationIfNeed(MovementInfo const& minfo, uint16 opcode)
 {
-    if (m_lastFallTime >= minfo.jump.fallTime || m_lastFallZ <= minfo.pos.GetPositionZ() || opcode == MSG_MOVE_FALL_LAND)
+    if (m_lastFallTimeClient >= minfo.jump.fallTime || m_lastFallZ <= minfo.pos.GetPositionZ() || opcode == MSG_MOVE_FALL_LAND)
         SetFallInformation(minfo.jump.fallTime, minfo.pos.GetPositionZ());
 }
 

src/server/game/Entities/Player/Player.h

@@ -2841,7 +2841,8 @@ class TC_GAME_API Player : public Unit, public GridObject<Player>
 
         MapReference m_mapRef;
 
-        uint32 m_lastFallTime;
+        uint32 m_lastFallTimeClient;
+        uint32 m_fallStartTimeServer;
         float  m_lastFallZ;
 
         int32 m_MirrorTimer[MAX_TIMERS];

src/server/game/World/World.cpp

@@ -1409,6 +1409,9 @@ void World::LoadConfigSettings(bool reload)
     // Whether to use LoS from game objects
     m_bool_configs[CONFIG_CHECK_GOBJECT_LOS] = sConfigMgr->GetBoolDefault("CheckGameObjectLoS", true);
 
+    // What happens with cheaters that delay their fall
+    m_int_configs[CONFIG_ANTICHEAT_FALL_PUNISHMENT] = sConfigMgr->GetIntDefault("Anticheat.FallDelayed", 1); // 1 - kill
+
     // call ScriptMgr if we're reloading the configuration
     if (reload)
         sScriptMgr->OnConfigLoad(reload);

src/server/game/World/World.h

@@ -413,6 +413,7 @@ enum WorldIntConfigs
     CONFIG_RESPAWN_DYNAMICMINIMUM_CREATURE,
     CONFIG_RESPAWN_DYNAMICMINIMUM_GAMEOBJECT,
     CONFIG_RESPAWN_GUIDWARNING_FREQUENCY,
+    CONFIG_ANTICHEAT_FALL_PUNISHMENT,
     INT_CONFIG_VALUE_COUNT
 };
 

src/server/worldserver/worldserver.conf.dist

@@ -1212,6 +1212,16 @@ Account.PasswordChangeSecurity = 0
 
 BirthdayTime = 1222964635
 
+#
+#   Anticheat.FallDelayed
+#        Description: Decides what happens with players who show invalid fall behavior.
+#                     Can produce false positives in high latency situations.
+#                     2 - (Force disconnect from server)
+#        Default:     1 - (Kill player using fall damage)
+#                     0 - (Only log to console)
+
+Anticheat.FallDelayed = 1
+
 #
 ###################################################################################################