[CVE-2018-8505] Edge - Chakra::TypeConfusion_8_16 JIT - Qihoo 360

lib/Runtime/Language/JavascriptOperators.cpp

@@ -4950,13 +4950,18 @@ SetElementIHelper_INDEX_TYPE_IS_NUMBER:
                 }
                 else if (instanceType == TypeIds_NativeIntArray)
                 {
-                    // Only accept tagged int. Also covers case for MissingItem
+                    // Only accept tagged int.
                     if (!TaggedInt::Is(value))
                     {
                         return false;
                     }
                     int32 intValue = 0;
                     if (!MemsetConversion<int32, JavascriptConversion::ToInt32>(value, scriptContext, &intValue))
+                    {
+                        return false;
+                    }
+                     // Special case for missing item
+                    if (SparseArraySegment<int32>::IsMissingItem(&intValue))
                     {
                         return false;
                     }

lib/Runtime/Library/JavascriptArray.cpp

@@ -3424,16 +3424,12 @@ using namespace Js;
             {
                 if (TaggedInt::Is(aItem))
                 {
-                    pDestArray->DirectSetItemAt(idxDest, TaggedInt::ToInt32(aItem));
+                    int32 int32Value = TaggedInt::ToInt32(aItem);
+                    Assert(!SparseArraySegment<int32>::IsMissingItem(&int32Value));
+                    pDestArray->DirectSetItemAt(idxDest, int32Value);
                 }
                 else
                 {
-#if DBG
-                    int32 int32Value;
-                    Assert(
-                        JavascriptNumber::TryGetInt32Value(JavascriptNumber::GetValue(aItem), &int32Value) &&
-                        !SparseArraySegment<int32>::IsMissingItem(&int32Value));
-#endif
                     pDestArray->DirectSetItemAt(idxDest, static_cast<int32>(JavascriptNumber::GetValue(aItem)));
                 }
                 ++idxDest;