5 files changed, 25 insertions, 1 deletions
diff --git a/poi-integration/src/test/java/org/apache/poi/stress/XSSFFileHandler.java b/poi-integration/src/test/java/org/apache/poi/stress/XSSFFileHandler.java
index d8c1108906..1f75723c66 100644
--- a/poi-integration/src/test/java/org/apache/poi/stress/XSSFFileHandler.java
+++ b/poi-integration/src/test/java/org/apache/poi/stress/XSSFFileHandler.java
@@ -28,6 +28,7 @@ import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.OutputStream;
 import java.io.PrintStream;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -54,6 +55,7 @@ import org.apache.poi.ss.usermodel.Sheet;
 import org.apache.poi.util.IOUtils;
 import org.apache.poi.xssf.eventusermodel.XSSFReader;
 import org.apache.poi.xssf.extractor.XSSFExportToXml;
+import org.apache.poi.xssf.streaming.SXSSFWorkbook;
 import org.apache.poi.xssf.usermodel.XSSFMap;
 import org.apache.poi.xssf.usermodel.XSSFSheet;
 import org.apache.poi.xssf.usermodel.XSSFWorkbook;
@@ -115,6 +117,13 @@ public class XSSFFileHandler extends SpreadsheetHandler {
         // and finally ensure that exporting to XML works
         exportToXML(wb);
 
+        // also try to read and write the sheet via SXSSF
+        try (SXSSFWorkbook swb = new SXSSFWorkbook(wb)) {
+            try (OutputStream out = NullOutputStream.INSTANCE) {
+                swb.write(out);
+            }
+        }
+
         // this allows to trigger a heap-dump at this point to see which memory is still allocated
         //HeapDump.dumpHeap("/tmp/poi.hprof", false);
 
diff --git a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFTable.java b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFTable.java
index 535683be6a..d9f7189446 100644
--- a/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFTable.java
+++ b/poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFTable.java
@@ -803,7 +803,12 @@ public class XSSFTable extends POIXMLDocumentPart implements Table {
      *  manually add cells with values of "Column1", "Column2" etc first.
      */
     public void updateHeaders() {
-        XSSFSheet sheet = (XSSFSheet)getParent();
+        final POIXMLDocumentPart parent = getParent();
+        if (!(parent instanceof XSSFSheet)) {
+            throw new IllegalArgumentException("Had unexpected type of parent: " + (parent == null ? "<null>" : parent.getClass()));
+        }
+
+        XSSFSheet sheet = (XSSFSheet) parent;
         CellReference ref = getStartCellReference();
         if (ref == null) return;
 
diff --git a/poi-ooxml/src/test/java/org/apache/poi/xssf/streaming/TestSXSSFWorkbook.java b/poi-ooxml/src/test/java/org/apache/poi/xssf/streaming/TestSXSSFWorkbook.java
index 6af4542525..1f57111839 100644
--- a/poi-ooxml/src/test/java/org/apache/poi/xssf/streaming/TestSXSSFWorkbook.java
+++ b/poi-ooxml/src/test/java/org/apache/poi/xssf/streaming/TestSXSSFWorkbook.java
@@ -33,6 +33,7 @@ import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.time.LocalDate;
 import java.util.Arrays;
 
@@ -725,4 +726,13 @@ public final class TestSXSSFWorkbook extends BaseTestXWorkbook {
         }
     }
 
+    @Test
+    void writeBrokenFile() throws IOException {
+        try (final Workbook wb = _testDataProvider.openSampleWorkbook("clusterfuzz-testcase-minimized-POIXSSFFuzzer-5185049589579776.xlsx")) {
+            try (OutputStream out = NullOutputStream.INSTANCE) {
+                assertThrows(IllegalArgumentException.class,
+                        () -> wb.write(out));
+            }
+        }
+    }
 }
diff --git a/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIXSSFFuzzer-5185049589579776.xlsx b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIXSSFFuzzer-5185049589579776.xlsx
new file mode 100644
index 0000000000..b14f41fa57
--- /dev/null
+++ b/test-data/spreadsheet/clusterfuzz-testcase-minimized-POIXSSFFuzzer-5185049589579776.xlsx
diff --git a/test-data/spreadsheet/stress.xls b/test-data/spreadsheet/stress.xls
index eeecaeb553..b4c297fe28 100644
--- a/test-data/spreadsheet/stress.xls
+++ b/test-data/spreadsheet/stress.xls