diff --git a/src/main/java/org/apache/commons/lang3/StringUtils.java b/src/main/java/org/apache/commons/lang3/StringUtils.java
index 02d32f8a091..7bc5d99c021 100644
--- a/src/main/java/org/apache/commons/lang3/StringUtils.java
+++ b/src/main/java/org/apache/commons/lang3/StringUtils.java
@@ -654,6 +654,15 @@ public static String center(String str, final int size, String padStr) {
         return rightPad(str, size, padStr);
     }
 
+    private static void checkFromToIndex(final int startIndex, final int endIndex, final int length) {
+        if (startIndex < 0) {
+            throw new ArrayIndexOutOfBoundsException(startIndex);
+        }
+        if (endIndex > length) {
+            throw new ArrayIndexOutOfBoundsException(endIndex);
+        }
+    }
+
     /**
      * Removes one newline from end of a String if it's there, otherwise leave it alone. A newline is &quot;{@code \n}&quot;, &quot;{@code \r}&quot;, or
      * &quot;{@code \r\n}&quot;.
@@ -3866,6 +3875,7 @@ public static String join(final boolean[] array, final char delimiter, final int
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -3943,6 +3953,7 @@ public static String join(final byte[] array, final char delimiter, final int st
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -4020,6 +4031,7 @@ public static String join(final char[] array, final char delimiter, final int st
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -4097,6 +4109,7 @@ public static String join(final double[] array, final char delimiter, final int
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -4174,6 +4187,7 @@ public static String join(final float[] array, final char delimiter, final int s
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -4251,6 +4265,7 @@ public static String join(final int[] array, final char delimiter, final int sta
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -4491,6 +4506,7 @@ public static String join(final long[] array, final char delimiter, final int st
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
@@ -4687,6 +4703,7 @@ public static String join(final short[] array, final char delimiter, final int s
         if (array == null) {
             return null;
         }
+        checkFromToIndex(startIndex, endIndex, array.length);
         final int count = endIndex - startIndex;
         if (count <= 0) {
             return EMPTY;
diff --git a/src/test/java/org/apache/commons/lang3/StringUtilsJoinExceptionTest.java b/src/test/java/org/apache/commons/lang3/StringUtilsJoinExceptionTest.java
new file mode 100644
index 00000000000..74ca21fdb2c
--- /dev/null
+++ b/src/test/java/org/apache/commons/lang3/StringUtilsJoinExceptionTest.java
@@ -0,0 +1,126 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.lang3;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTimeout;
+
+import java.time.Duration;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Primitive joins can OOM before index validation.
+ * <p>
+ * capacity() is called before bounds validation in join(byte[], char, int, int). An endIndex of Integer.MAX_VALUE causes an attempt to allocate ~8 GB before
+ * the array bounds are checked. Negative-startIndex bypass case.
+ * </p>
+ * <p>
+ * For {@code startIndex = -2_000_000_000, endIndex = 1, array.length = 2}: {@code count = endIndex - startIndex = 2_000_000_001}, which is positive (no
+ * overflow into negative territory), so the {@code count <= 0} early-return does not fire. The pre-existing {@code endIndex > array.length} check also passes
+ * (1 &lt; 2). The capacity allocation then attempts to size a StringBuilder for ~2 billion items, triggering OOM before the loop body would have caught the bad
+ * index.
+ * </p>
+ *
+ * Pre-patch: throws OutOfMemoryError or hangs for > 2 seconds. Post-patch: throws ArrayIndexOutOfBoundsException quickly (within 2 seconds).
+ */
+public class StringUtilsJoinExceptionTest {
+
+    private static final Class<ArrayIndexOutOfBoundsException> EXPECTED_EX = ArrayIndexOutOfBoundsException.class;
+    private static final Duration TIMEOUT = Duration.ofSeconds(2);
+
+    @Test
+    public void testBooleanJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new boolean[] { true }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testBooleanJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new boolean[] { true, false }, ',', -2_000_000_000, 1)));
+    }
+
+    @Test
+    public void testByteJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new byte[] { 1 }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testByteJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new byte[] { 1, 2 }, ',', -2_000_000_000, 1)));
+    }
+
+    @Test
+    public void testCharJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new char[] { 1 }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testCharJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new char[] { 1, 2 }, ',', -2_000_000_000, 1)));
+    }
+
+    @Test
+    public void testDoubleJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new double[] { 1 }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testDoubleJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new double[] { 1, 2 }, ',', Integer.MIN_VALUE + 100, 1)));
+    }
+
+    @Test
+    public void testFloatJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new float[] { 1 }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testFloatJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new float[] { 1, 2 }, ',', Integer.MIN_VALUE + 100, 1)));
+    }
+
+    @Test
+    public void testIntJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new int[] { 1 }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testIntJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new int[] { 1, 2 }, ',', Integer.MIN_VALUE + 100, 1)));
+    }
+
+    @Test
+    public void testLongJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new long[] { 1L }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testLongJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new long[] { 1L, 2L }, ',', -2_000_000_000, 1)));
+    }
+
+    @Test
+    public void testShortJoinValidatesEndIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new short[] { 1 }, ',', 0, Integer.MAX_VALUE)));
+    }
+
+    @Test
+    public void testShortJoinValidatesNegativeStartIndexBeforeCapacity() {
+        assertTimeout(TIMEOUT, () -> assertThrows(EXPECTED_EX, () -> StringUtils.join(new short[] { 1, 2 }, ',', -2_000_000_000, 1)));
+    }
+}