diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29e70c5026bb8..022cc8451a28c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -58,6 +58,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Remove query categorization changes ([#14759](https://github.com/opensearch-project/OpenSearch/pull/14759))
 
 ### Fixed
+- Fix allowUnmappedFields, mapUnmappedFieldAsString settings are not applied when parsing certain types of query string query ([#13957](https://github.com/opensearch-project/OpenSearch/pull/13957))
 - Fix bug in SBP cancellation logic ([#13259](https://github.com/opensearch-project/OpenSearch/pull/13474))
 - Fix handling of Short and Byte data types in ScriptProcessor ingest pipeline ([#14379](https://github.com/opensearch-project/OpenSearch/issues/14379))
 - Switch to iterative version of WKT format parser ([#14086](https://github.com/opensearch-project/OpenSearch/pull/14086))
diff --git a/modules/percolator/src/yamlRestTest/resources/rest-api-spec/test/10_basic.yml b/modules/percolator/src/yamlRestTest/resources/rest-api-spec/test/10_basic.yml
index 35ebb2b099139..61f79326dab06 100644
--- a/modules/percolator/src/yamlRestTest/resources/rest-api-spec/test/10_basic.yml
+++ b/modules/percolator/src/yamlRestTest/resources/rest-api-spec/test/10_basic.yml
@@ -83,3 +83,48 @@
                 index: documents_index
                 id: some_id
   - match:  { responses.0.hits.total:     1  }
+
+  - do:
+      catch: bad_request
+      index:
+        index: queries_index
+        body:
+          query:
+            query_string:
+              query: "unmapped: *"
+
+  - do:
+      catch: bad_request
+      index:
+        index: queries_index
+        body:
+          query:
+            query_string:
+              query: "_exists_: unmappedField"
+
+  - do:
+        catch: bad_request
+        index:
+          index: queries_index
+          body:
+            query:
+              query_string:
+                query: "unmappedField: <100"
+
+  - do:
+      catch: bad_request
+      index:
+        index: queries_index
+        body:
+          query:
+            query_string:
+              query: "unmappedField: test~"
+
+  - do:
+      catch: bad_request
+      index:
+        index: queries_index
+        body:
+          query:
+            query_string:
+              query: "unmappedField: test*"
diff --git a/server/src/main/java/org/opensearch/index/query/ExistsQueryBuilder.java b/server/src/main/java/org/opensearch/index/query/ExistsQueryBuilder.java
index 3011a48fbb296..6ae40fe1b1e64 100644
--- a/server/src/main/java/org/opensearch/index/query/ExistsQueryBuilder.java
+++ b/server/src/main/java/org/opensearch/index/query/ExistsQueryBuilder.java
@@ -230,20 +230,16 @@ private static Collection<String> getMappedField(QueryShardContext context, Stri
         if (context.getObjectMapper(fieldPattern) != null) {
             // the _field_names field also indexes objects, so we don't have to
             // do any more work to support exists queries on whole objects
-            fields = Collections.singleton(fieldPattern);
+            return Collections.singleton(fieldPattern);
         } else {
             fields = context.simpleMatchToIndexNames(fieldPattern);
         }
 
         if (fields.size() == 1) {
             String field = fields.iterator().next();
-            MappedFieldType fieldType = context.getMapperService().fieldType(field);
+            MappedFieldType fieldType = context.fieldMapper(field);
             if (fieldType == null) {
-                // The field does not exist as a leaf but could be an object so
-                // check for an object mapper
-                if (context.getObjectMapper(field) == null) {
-                    return Collections.emptySet();
-                }
+                return Collections.emptySet();
             }
         }
 
diff --git a/server/src/main/java/org/opensearch/index/search/QueryParserHelper.java b/server/src/main/java/org/opensearch/index/search/QueryParserHelper.java
index 06f450f090e63..603e81f6bf113 100644
--- a/server/src/main/java/org/opensearch/index/search/QueryParserHelper.java
+++ b/server/src/main/java/org/opensearch/index/search/QueryParserHelper.java
@@ -143,7 +143,7 @@ static Map<String, Float> resolveMappingField(
                 fieldName = fieldName + fieldSuffix;
             }
 
-            MappedFieldType fieldType = context.getMapperService().fieldType(fieldName);
+            MappedFieldType fieldType = context.fieldMapper(fieldName);
             if (fieldType == null) {
                 fieldType = context.resolveDerivedFieldType(fieldName);
             }