diff --git a/src/main/java/de/rub/nds/modifiablevariable/ModifiableVariable.java b/src/main/java/de/rub/nds/modifiablevariable/ModifiableVariable.java
index dfa145da..9e6c34b9 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/ModifiableVariable.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/ModifiableVariable.java
@@ -113,10 +113,10 @@ public void addModification(VariableModification<E> modification) {
     /**
      * Returns all modifications that are set for this modifiable variable.
      *
-     * @return The list of modifications or null if no modifications are set
+     * @return A copy of the list of modifications or null if no modifications are set
      */
     public LinkedList<VariableModification<E>> getModifications() {
-        return modifications;
+        return modifications == null ? null : new LinkedList<>(modifications);
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayAppendValueModification.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayAppendValueModification.java
index 46e59044..bff6faf2 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayAppendValueModification.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayAppendValueModification.java
@@ -51,8 +51,8 @@ private ByteArrayAppendValueModification() {
      */
     public ByteArrayAppendValueModification(byte[] bytesToAppend) {
         super();
-        this.bytesToAppend =
-                Objects.requireNonNull(bytesToAppend, "bytesToAppend must not be null");
+        Objects.requireNonNull(bytesToAppend, "bytesToAppend must not be null");
+        this.bytesToAppend = bytesToAppend.clone();
     }
 
     /**
@@ -105,7 +105,7 @@ protected byte[] modifyImplementationHook(byte[] input) {
      * @return The bytes to append
      */
     public byte[] getBytesToAppend() {
-        return bytesToAppend;
+        return bytesToAppend == null ? null : bytesToAppend.clone();
     }
 
     /**
@@ -115,8 +115,8 @@ public byte[] getBytesToAppend() {
      * @throws NullPointerException if bytesToAppend is null
      */
     public void setBytesToAppend(byte[] bytesToAppend) {
-        this.bytesToAppend =
-                Objects.requireNonNull(bytesToAppend, "BytesToAppend must not be null");
+        Objects.requireNonNull(bytesToAppend, "BytesToAppend must not be null");
+        this.bytesToAppend = bytesToAppend.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayExplicitValueModification.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayExplicitValueModification.java
index 28b4a6b1..3cb13342 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayExplicitValueModification.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayExplicitValueModification.java
@@ -44,8 +44,8 @@ private ByteArrayExplicitValueModification() {
      */
     public ByteArrayExplicitValueModification(byte[] explicitValue) {
         super();
-        this.explicitValue =
-                Objects.requireNonNull(explicitValue, "ExplicitValue must not be null");
+        Objects.requireNonNull(explicitValue, "ExplicitValue must not be null");
+        this.explicitValue = explicitValue.clone();
     }
 
     /**
@@ -91,7 +91,7 @@ protected byte[] modifyImplementationHook(byte[] input) {
      * @return The explicit byte array
      */
     public byte[] getExplicitValue() {
-        return explicitValue;
+        return explicitValue == null ? null : explicitValue.clone();
     }
 
     /**
@@ -100,8 +100,8 @@ public byte[] getExplicitValue() {
      * @param explicitValue The new explicit byte array to use
      */
     public void setExplicitValue(byte[] explicitValue) {
-        this.explicitValue =
-                Objects.requireNonNull(explicitValue, "ExplicitValue must not be null");
+        Objects.requireNonNull(explicitValue, "ExplicitValue must not be null");
+        this.explicitValue = explicitValue.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayInsertValueModification.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayInsertValueModification.java
index 2419abcd..3c37dbe0 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayInsertValueModification.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayInsertValueModification.java
@@ -56,8 +56,8 @@ private ByteArrayInsertValueModification() {
      */
     public ByteArrayInsertValueModification(byte[] bytesToInsert, int startPosition) {
         super();
-        this.bytesToInsert =
-                Objects.requireNonNull(bytesToInsert, "BytesToInsert must not be null");
+        Objects.requireNonNull(bytesToInsert, "BytesToInsert must not be null");
+        this.bytesToInsert = bytesToInsert.clone();
         this.startPosition = startPosition;
     }
 
@@ -129,7 +129,7 @@ protected byte[] modifyImplementationHook(byte[] input) {
      * @return The bytes to insert
      */
     public byte[] getBytesToInsert() {
-        return bytesToInsert;
+        return bytesToInsert == null ? null : bytesToInsert.clone();
     }
 
     /**
@@ -139,8 +139,8 @@ public byte[] getBytesToInsert() {
      * @throws NullPointerException if bytesToInsert is null
      */
     public void setBytesToInsert(byte[] bytesToInsert) {
-        this.bytesToInsert =
-                Objects.requireNonNull(bytesToInsert, "bytesToInsert must not be null");
+        Objects.requireNonNull(bytesToInsert, "bytesToInsert must not be null");
+        this.bytesToInsert = bytesToInsert.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayPrependValueModification.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayPrependValueModification.java
index 3f32c70d..f017d0a5 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayPrependValueModification.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayPrependValueModification.java
@@ -52,8 +52,8 @@ private ByteArrayPrependValueModification() {
      */
     public ByteArrayPrependValueModification(byte[] bytesToPrepend) {
         super();
-        this.bytesToPrepend =
-                Objects.requireNonNull(bytesToPrepend, "bytesToPrepend must not be null");
+        Objects.requireNonNull(bytesToPrepend, "bytesToPrepend must not be null");
+        this.bytesToPrepend = bytesToPrepend.clone();
     }
 
     /**
@@ -107,7 +107,7 @@ protected byte[] modifyImplementationHook(byte[] input) {
      * @return The bytes to prepend
      */
     public byte[] getBytesToPrepend() {
-        return bytesToPrepend;
+        return bytesToPrepend == null ? null : bytesToPrepend.clone();
     }
 
     /**
@@ -117,8 +117,8 @@ public byte[] getBytesToPrepend() {
      * @throws NullPointerException if bytesToPrepend is null
      */
     public void setBytesToPrepend(byte[] bytesToPrepend) {
-        this.bytesToPrepend =
-                Objects.requireNonNull(bytesToPrepend, "bytesToPrepend must not be null");
+        Objects.requireNonNull(bytesToPrepend, "bytesToPrepend must not be null");
+        this.bytesToPrepend = bytesToPrepend.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayShuffleModification.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayShuffleModification.java
index ab301c23..00fb42d2 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayShuffleModification.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayShuffleModification.java
@@ -45,7 +45,8 @@ private ByteArrayShuffleModification() {
      */
     public ByteArrayShuffleModification(int[] shuffle) {
         super();
-        this.shuffle = Objects.requireNonNull(shuffle, "Shuffle pattern must not be null");
+        Objects.requireNonNull(shuffle, "Shuffle pattern must not be null");
+        this.shuffle = shuffle.clone();
     }
 
     /**
@@ -113,7 +114,7 @@ protected byte[] modifyImplementationHook(byte[] input) {
      * @return The int array containing the shuffle pattern
      */
     public int[] getShuffle() {
-        return shuffle;
+        return shuffle == null ? null : shuffle.clone();
     }
 
     /**
@@ -123,7 +124,8 @@ public int[] getShuffle() {
      * @throws NullPointerException if shuffle is null
      */
     public void setShuffle(int[] shuffle) {
-        this.shuffle = Objects.requireNonNull(shuffle, "Shuffle pattern must not be null");
+        Objects.requireNonNull(shuffle, "Shuffle pattern must not be null");
+        this.shuffle = shuffle.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayXorModification.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayXorModification.java
index f039c729..dd0e16b2 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayXorModification.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ByteArrayXorModification.java
@@ -49,7 +49,8 @@ private ByteArrayXorModification() {
      */
     public ByteArrayXorModification(byte[] xor, int startPosition) {
         super();
-        this.xor = Objects.requireNonNull(xor, "XOR array must not be null");
+        Objects.requireNonNull(xor, "XOR array must not be null");
+        this.xor = xor.clone();
         this.startPosition = startPosition;
     }
 
@@ -126,10 +127,10 @@ protected byte[] modifyImplementationHook(byte[] input) {
     /**
      * Gets the byte array used for the XOR operation.
      *
-     * @return The XOR byte array
+     * @return A copy of the XOR byte array
      */
     public byte[] getXor() {
-        return xor;
+        return xor == null ? null : xor.clone();
     }
 
     /**
@@ -138,7 +139,7 @@ public byte[] getXor() {
      * @param xor The new XOR byte array
      */
     public void setXor(byte[] xor) {
-        this.xor = xor;
+        this.xor = xor == null ? null : xor.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ModifiableByteArray.java b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ModifiableByteArray.java
index 5aff26db..a9547288 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/bytearray/ModifiableByteArray.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/bytearray/ModifiableByteArray.java
@@ -59,7 +59,7 @@ public ModifiableByteArray() {
      */
     public ModifiableByteArray(byte[] originalValue) {
         super();
-        this.originalValue = originalValue;
+        this.originalValue = originalValue == null ? null : originalValue.clone();
     }
 
     /**
@@ -99,7 +99,7 @@ public ModifiableByteArray createCopy() {
     @Override
     @XmlJavaTypeAdapter(UnformattedByteArrayAdapter.class)
     public byte[] getOriginalValue() {
-        return originalValue;
+        return originalValue == null ? null : originalValue.clone();
     }
 
     /**
@@ -109,7 +109,7 @@ public byte[] getOriginalValue() {
      */
     @Override
     public void setOriginalValue(byte[] originalValue) {
-        this.originalValue = originalValue;
+        this.originalValue = originalValue == null ? null : originalValue.clone();
     }
 
     /**
@@ -121,7 +121,7 @@ public void setOriginalValue(byte[] originalValue) {
      */
     @XmlJavaTypeAdapter(UnformattedByteArrayAdapter.class)
     public byte[] getAssertEquals() {
-        return assertEquals;
+        return assertEquals == null ? null : assertEquals.clone();
     }
 
     /**
@@ -130,7 +130,7 @@ public byte[] getAssertEquals() {
      * @param assertEquals The expected byte array value
      */
     public void setAssertEquals(byte[] assertEquals) {
-        this.assertEquals = assertEquals;
+        this.assertEquals = assertEquals == null ? null : assertEquals.clone();
     }
 
     /**
diff --git a/src/main/java/de/rub/nds/modifiablevariable/util/ComparableByteArray.java b/src/main/java/de/rub/nds/modifiablevariable/util/ComparableByteArray.java
index af2400ae..cfcc76a4 100644
--- a/src/main/java/de/rub/nds/modifiablevariable/util/ComparableByteArray.java
+++ b/src/main/java/de/rub/nds/modifiablevariable/util/ComparableByteArray.java
@@ -44,7 +44,7 @@ private ComparableByteArray() {
      */
     public ComparableByteArray(byte[] array) {
         super();
-        this.array = array;
+        this.array = array == null ? null : array.clone();
     }
 
     /**
@@ -53,7 +53,7 @@ public ComparableByteArray(byte[] array) {
      * @return A the wrapped byte array
      */
     public byte[] getArray() {
-        return array;
+        return array == null ? null : array.clone();
     }
 
     /**
@@ -62,7 +62,7 @@ public byte[] getArray() {
      * @param array The new byte array to wrap
      */
     public void setArray(byte[] array) {
-        this.array = array;
+        this.array = array == null ? null : array.clone();
     }
 
     /**