Core/Spells: Implement SPELL_ATTR6_IGNORE_CROWD_CONTROL_TARGETS (0x00000100). Spells with this attribute flag (Avenger's Shield, Hammer of Righteousness, Shield of Righteousness, Felguard Cleave, Fel Iron Bomb) will ignore secondary targets that are under the effect of crowd control aura's.

Thanks to Shauren for advices.

src/server/game/Miscellaneous/SharedDefines.h

@@ -487,7 +487,7 @@ enum SpellAttr6
     SPELL_ATTR6_UNK5                             = 0x00000020, //  5
     SPELL_ATTR6_UNK6                             = 0x00000040, //  6
     SPELL_ATTR6_UNK7                             = 0x00000080, //  7
-    SPELL_ATTR6_UNK8                             = 0x00000100, //  8
+    SPELL_ATTR6_IGNORE_CROWD_CONTROL_TARGETS     = 0x00000100, //  8
     SPELL_ATTR6_UNK9                             = 0x00000200, //  9
     SPELL_ATTR6_UNK10                            = 0x00000400, // 10
     SPELL_ATTR6_NOT_IN_RAID_INSTANCE             = 0x00000800, // 11 not usable in raid instance

src/server/game/Spells/Spell.cpp

@@ -1790,15 +1790,19 @@ void Spell::SearchChainTarget(std::list<Unit*> &TagUnitMap, float max_range, uin
             tempUnitMap.sort(Trinity::ObjectDistanceOrderPred(cur));
             next = tempUnitMap.begin();
 
-            if (cur->GetDistance(*next) > CHAIN_SPELL_JUMP_RADIUS)
+            if (cur->GetDistance(*next) > CHAIN_SPELL_JUMP_RADIUS)      // Don't search beyond the max jump radius
                 break;
-            while ((m_spellInfo->DmgClass == SPELL_DAMAGE_CLASS_MELEE
+
+            // Check if (*next) is a valid chain target. If not, don't add to TagUnitMap, and repeat loop.
+            // If you want to add any conditions to exclude a target from TagUnitMap, add condition in this while() loop.
+            while ((m_spellInfo->DmgClass == SPELL_DAMAGE_CLASS_MELEE   
                 && !m_caster->isInFrontInMap(*next, max_range))
                 || !m_caster->canSeeOrDetect(*next)
-                || !cur->IsWithinLOSInMap(*next))
+                || !cur->IsWithinLOSInMap(*next)
+                || ((GetSpellInfo()->AttributesEx6 & SPELL_ATTR6_IGNORE_CROWD_CONTROL_TARGETS) && !(*next)->CanFreeMove()))
             {
                 ++next;
-                if (next == tempUnitMap.end() || cur->GetDistance(*next) > CHAIN_SPELL_JUMP_RADIUS)
+                if (next == tempUnitMap.end() || cur->GetDistance(*next) > CHAIN_SPELL_JUMP_RADIUS) // Don't search beyond the max jump radius
                     return;
             }
         }