7 files changed, 71 insertions, 1 deletions
diff --git a/poi-ooxml/src/test/java/org/apache/poi/xssf/usermodel/TestXSSFDataFormat.java b/poi-ooxml/src/test/java/org/apache/poi/xssf/usermodel/TestXSSFDataFormat.java
index fe4aa0a00a..bc6ddf0c62 100644
--- a/poi-ooxml/src/test/java/org/apache/poi/xssf/usermodel/TestXSSFDataFormat.java
+++ b/poi-ooxml/src/test/java/org/apache/poi/xssf/usermodel/TestXSSFDataFormat.java
@@ -21,6 +21,7 @@ import static org.apache.poi.xssf.XSSFTestDataSamples.openSampleWorkbook;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import java.io.IOException;
+import java.util.Date;
 
 import org.apache.poi.ss.formula.ConditionalFormattingEvaluator;
 import org.apache.poi.ss.formula.WorkbookEvaluatorProvider;
@@ -120,4 +121,37 @@ public final class TestXSSFDataFormat extends BaseTestDataFormat {
             assertEquals("6.75", formatter.formatCellValue(d1));
         }
     }
+
+    @Test
+    public void testFormatCellValue() throws IOException {
+        DataFormatter df = new DataFormatter();
+
+        assertEquals("", df.formatCellValue(null));
+
+        try (Workbook wb = new XSSFWorkbook()) {
+            Cell cell = wb.createSheet("test").createRow(0).createCell(0);
+            assertEquals("", df.formatCellValue(cell));
+
+            cell.setCellValue(123);
+            assertEquals("123", df.formatCellValue(cell));
+
+            cell.setCellValue(new Date(234092383));
+            assertEquals("25571.75107", df.formatCellValue(cell));
+
+            cell.setCellValue("abcdefgh");
+            assertEquals("abcdefgh", df.formatCellValue(cell));
+
+            cell.setCellValue(true);
+            assertEquals("TRUE", df.formatCellValue(cell));
+
+            CellStyle cellStyle = wb.createCellStyle();
+            cellStyle.setDataFormat((short)14);
+            cell.setCellStyle(cellStyle);
+            cell.setCellValue(new Date(234092383));
+            assertEquals("1/3/70", df.formatCellValue(cell));
+
+            cellStyle.setDataFormat((short)9999);
+            assertEquals("25571.751069247686", df.formatCellValue(cell));
+        }
+    }
 }
diff --git a/poi/src/main/java/org/apache/poi/ss/usermodel/DataFormatter.java b/poi/src/main/java/org/apache/poi/ss/usermodel/DataFormatter.java
index 35e5ff55d6..f94e6893f7 100644
--- a/poi/src/main/java/org/apache/poi/ss/usermodel/DataFormatter.java
+++ b/poi/src/main/java/org/apache/poi/ss/usermodel/DataFormatter.java
@@ -922,7 +922,7 @@ public class DataFormatter {
                 sdf.setTimeZone(LocaleUtil.getUserTimeZone());
                 dateFormat = sdf;
             } else {
-                dateFormat = defaultNumFormat;
+                dateFormat = defaultDateformat;
             }
         }
         synchronized (dateFormat) {
diff --git a/poi/src/test/java/org/apache/poi/hssf/dev/TestBiffViewer.java b/poi/src/test/java/org/apache/poi/hssf/dev/TestBiffViewer.java
index 491d68d159..d23f1dbece 100644
--- a/poi/src/test/java/org/apache/poi/hssf/dev/TestBiffViewer.java
+++ b/poi/src/test/java/org/apache/poi/hssf/dev/TestBiffViewer.java
@@ -46,6 +46,7 @@ class TestBiffViewer extends BaseTestIteratingXLS {
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-5889658057523200.xls", IndexOutOfBoundsException.class);
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-5175219985448960.xls", IndexOutOfBoundsException.class);
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6137883240824832.xls", IndexOutOfBoundsException.class);
+        excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6483562584932352.xls", IndexOutOfBoundsException.class);
 
         return excludes;
     }
diff --git a/poi/src/test/java/org/apache/poi/hssf/dev/TestRecordLister.java b/poi/src/test/java/org/apache/poi/hssf/dev/TestRecordLister.java
index 7f1c1f4561..34359e1d2e 100644
--- a/poi/src/test/java/org/apache/poi/hssf/dev/TestRecordLister.java
+++ b/poi/src/test/java/org/apache/poi/hssf/dev/TestRecordLister.java
@@ -49,6 +49,7 @@ class TestRecordLister extends BaseTestIteratingXLS {
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-5889658057523200.xls", IndexOutOfBoundsException.class);
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-5175219985448960.xls", RecordFormatException.class);
         excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6137883240824832.xls", RecordFormatException.class);
+        excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6483562584932352.xls", RecordFormatException.class);
 
         return excludes;
     }
diff --git a/poi/src/test/java/org/apache/poi/ss/usermodel/TestDataFormatter.java b/poi/src/test/java/org/apache/poi/ss/usermodel/TestDataFormatter.java
index 0d6c1af5b9..31cfa031b0 100644
--- a/poi/src/test/java/org/apache/poi/ss/usermodel/TestDataFormatter.java
+++ b/poi/src/test/java/org/apache/poi/ss/usermodel/TestDataFormatter.java
@@ -35,6 +35,8 @@ import java.util.Locale;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
 
+import javax.swing.text.DateFormatter;
+
 import org.apache.poi.POITestCase;
 import org.apache.poi.hssf.HSSFTestDataSamples;
 import org.apache.poi.hssf.usermodel.HSSFWorkbook;
@@ -1162,4 +1164,36 @@ class TestDataFormatter {
         return true;
     }
 
+    @Test
+    public void testFormatCellValue() throws IOException {
+        DataFormatter df = new DataFormatter();
+
+        assertEquals("", df.formatCellValue(null));
+
+        try (Workbook wb = new HSSFWorkbook()) {
+            Cell cell = wb.createSheet("test").createRow(0).createCell(0);
+            assertEquals("", df.formatCellValue(cell));
+
+            cell.setCellValue(123);
+            assertEquals("123", df.formatCellValue(cell));
+
+            cell.setCellValue(new Date(234092383));
+            assertEquals("25571.75107", df.formatCellValue(cell));
+
+            cell.setCellValue("abcdefgh");
+            assertEquals("abcdefgh", df.formatCellValue(cell));
+
+            cell.setCellValue(true);
+            assertEquals("TRUE", df.formatCellValue(cell));
+
+            CellStyle cellStyle = wb.createCellStyle();
+            cellStyle.setDataFormat((short)14);
+            cell.setCellStyle(cellStyle);
+            cell.setCellValue(new Date(234092383));
+            assertEquals("1/3/70", df.formatCellValue(cell));
+
+            cellStyle.setDataFormat((short)9999);
+            assertEquals("25571.751069247686", df.formatCellValue(cell));
+        }
+    }
 }
diff --git a/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIHSSFFuzzer-6483562584932352.xls b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIHSSFFuzzer-6483562584932352.xls
new file mode 100644
index 0000000000..f2ec6f113b
--- /dev/null
+++ b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIHSSFFuzzer-6483562584932352.xls
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index 98ce7f52d6..0c9f727189 100644
--- a/test-data/spreadsheet/stress.xls
+++ b/test-data/spreadsheet/stress.xls