diff --git a/poi-scratchpad/src/main/java/org/apache/poi/hdgf/chunks/ChunkHeader.java b/poi-scratchpad/src/main/java/org/apache/poi/hdgf/chunks/ChunkHeader.java
index 8f31139f535..209550a7864 100644
--- a/poi-scratchpad/src/main/java/org/apache/poi/hdgf/chunks/ChunkHeader.java
+++ b/poi-scratchpad/src/main/java/org/apache/poi/hdgf/chunks/ChunkHeader.java
@@ -50,7 +50,11 @@ public static ChunkHeader createChunkHeader(int documentVersion, byte[] data, in
             ch.setType((int) LittleEndian.getUInt(data, offset));
             ch.setId((int) LittleEndian.getUInt(data, offset + 4));
             ch.setUnknown1((int) LittleEndian.getUInt(data, offset + 8));
-            ch.setLength((int) LittleEndian.getUInt(data, offset + 12));
+            // Match the v4/v5 branch below: reject lengths that would silently
+            // truncate when narrowing the uint32 to a signed int, rather than
+            // letting a wrapped value flow into the offset arithmetic in
+            // ChunkFactory.createChunk (offset + getLength() + sizeInBytes).
+            ch.setLength(Math.toIntExact(LittleEndian.getUInt(data, offset + 12)));
             ch.setUnknown2(LittleEndian.getShort(data, offset + 16));
             ch.setUnknown3(LittleEndian.getUByte(data, offset + 18));
 
diff --git a/poi-scratchpad/src/test/java/org/apache/poi/hdgf/chunks/TestChunks.java b/poi-scratchpad/src/test/java/org/apache/poi/hdgf/chunks/TestChunks.java
index 58254a5933c..a5a74a48537 100644
--- a/poi-scratchpad/src/test/java/org/apache/poi/hdgf/chunks/TestChunks.java
+++ b/poi-scratchpad/src/test/java/org/apache/poi/hdgf/chunks/TestChunks.java
@@ -20,12 +20,14 @@ Licensed to the Apache Software Foundation (ASF) under one or more
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.IOException;
 
 import org.apache.poi.hdgf.chunks.ChunkFactory.CommandDefinition;
 import org.apache.poi.poifs.storage.RawDataUtil;
+import org.apache.poi.util.LittleEndian;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 
@@ -62,6 +64,50 @@ void testChunkHeaderA() {
         assertTrue(header.hasSeparator());
     }
 
+    /**
+     * A v6+ chunk header reads its Length field as a 32-bit unsigned integer.
+     * A crafted file with Length > Integer.MAX_VALUE used to be silently
+     * narrowed via a plain {@code (int)} cast, letting the wrapped value flow
+     * into the offset arithmetic in {@code ChunkFactory.createChunk}
+     * ({@code offset + getLength() + sizeInBytes}). Match the v4/v5 branch,
+     * which has always used {@code Math.toIntExact} for its Length field, and
+     * reject the input up-front.
+     */
+    @Test
+    void testV11RejectsOversizedLength() {
+        // 19-byte v6+ header: type, id, unknown1, length, unknown2 (short), unknown3 (ubyte)
+        byte[] header = new byte[19];
+        LittleEndian.putUInt(header, 0,  0x46L);            // type
+        LittleEndian.putUInt(header, 4,  0xFFFFFFFFL);      // id (allowed -1 sentinel)
+        LittleEndian.putUInt(header, 8,  0x02L);            // unknown1
+        LittleEndian.putUInt(header, 12, 0x80000001L);      // length: would wrap to a negative int
+        LittleEndian.putShort(header, 16, (short)0);
+        header[18] = 0;
+
+        assertThrows(ArithmeticException.class,
+                () -> ChunkHeader.createChunkHeader(11, header, 0));
+    }
+
+    /**
+     * Lengths up to {@code Integer.MAX_VALUE} (still nonsensically large but
+     * representable) must continue to parse — the hardening is only meant to
+     * catch the silent-narrowing case, not to introduce a new lower ceiling.
+     * Downstream checks (e.g. {@code IOUtils.safelyClone}) handle bounding.
+     */
+    @Test
+    void testV11AcceptsMaxIntLength() {
+        byte[] header = new byte[19];
+        LittleEndian.putUInt(header, 0,  0x46L);
+        LittleEndian.putUInt(header, 4,  0x01L);
+        LittleEndian.putUInt(header, 8,  0x02L);
+        LittleEndian.putUInt(header, 12, Integer.MAX_VALUE & 0xFFFFFFFFL);
+        LittleEndian.putShort(header, 16, (short)0);
+        header[18] = 0;
+
+        ChunkHeader h = ChunkHeader.createChunkHeader(11, header, 0);
+        assertEquals(Integer.MAX_VALUE, h.getLength());
+    }
+
     @Test
     void testChunkHeaderB() {
         ChunkHeader h = ChunkHeader.createChunkHeader(11, data_b, 0);