diff --git a/src/main/java/com/clearfolio/viewer/config/ArtifactStoreProperties.java b/src/main/java/com/clearfolio/viewer/config/ArtifactStoreProperties.java
index 3f39c5b00..b158ce6aa 100644
--- a/src/main/java/com/clearfolio/viewer/config/ArtifactStoreProperties.java
+++ b/src/main/java/com/clearfolio/viewer/config/ArtifactStoreProperties.java
@@ -42,15 +42,24 @@ public String getMode() {
     }
 
     /**
-     * Sets the artifact store mode; blank or null values fall back to the
-     * disk-backed default, and any value other than {@link #MODE_IN_MEMORY}
-     * selects the disk-backed store.
+     * Sets the artifact store mode. Blank or null values fall back to the
+     * disk-backed default; unsupported non-blank modes are rejected so a
+     * deployment cannot silently persist artifacts to a different store than
+     * the operator intended.
      *
      * @param mode artifact store mode
+     * @throws IllegalArgumentException when a non-blank mode is unsupported
      */
     public void setMode(String mode) {
         String sanitized = sanitize(mode);
-        this.mode = sanitized.isEmpty() ? MODE_FILESYSTEM : sanitized;
+        if (sanitized.isEmpty()) {
+            this.mode = MODE_FILESYSTEM;
+            return;
+        }
+        if (!MODE_FILESYSTEM.equals(sanitized) && !MODE_IN_MEMORY.equals(sanitized)) {
+            throw new IllegalArgumentException("unsupported artifact store mode");
+        }
+        this.mode = sanitized;
     }
 
     /**
@@ -86,6 +95,9 @@ private static String sanitize(String value) {
         if (value == null) {
             return "";
         }
-        return value.replace("\u0000", "").strip().toLowerCase(Locale.ROOT);
+        if (value.indexOf('\u0000') >= 0) {
+            throw new IllegalArgumentException("unsupported artifact store mode: contains NUL");
+        }
+        return value.strip().toLowerCase(Locale.ROOT);
     }
 }
diff --git a/src/test/java/com/clearfolio/viewer/config/ArtifactStorePropertiesTest.java b/src/test/java/com/clearfolio/viewer/config/ArtifactStorePropertiesTest.java
index 357ab2c3b..602e50f53 100644
--- a/src/test/java/com/clearfolio/viewer/config/ArtifactStorePropertiesTest.java
+++ b/src/test/java/com/clearfolio/viewer/config/ArtifactStorePropertiesTest.java
@@ -2,6 +2,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.junit.jupiter.api.Test;
@@ -27,6 +28,17 @@ void setModeNormalizesCaseAndWhitespace() {
         assertTrue(properties.isInMemoryMode());
     }
 
+    @Test
+    void setModeAcceptsExplicitFilesystemMode() {
+        ArtifactStoreProperties properties = new ArtifactStoreProperties();
+        properties.setMode(ArtifactStoreProperties.MODE_IN_MEMORY);
+
+        properties.setMode("  FILESYSTEM  ");
+
+        assertEquals(ArtifactStoreProperties.MODE_FILESYSTEM, properties.getMode());
+        assertFalse(properties.isInMemoryMode());
+    }
+
     @Test
     void setModeFallsBackToFilesystemForNullAndBlankValues() {
         ArtifactStoreProperties properties = new ArtifactStoreProperties();
@@ -39,13 +51,28 @@ void setModeFallsBackToFilesystemForNullAndBlankValues() {
     }
 
     @Test
-    void setModeKeepsUnknownValuesWithoutSelectingInMemory() {
+    void setModeRejectsUnknownStorageModes() {
         ArtifactStoreProperties properties = new ArtifactStoreProperties();
 
-        properties.setMode("cloud");
+        IllegalArgumentException error = assertThrows(
+                IllegalArgumentException.class,
+                () -> properties.setMode("cloud://tenant-secret")
+        );
 
-        assertEquals("cloud", properties.getMode());
-        assertFalse(properties.isInMemoryMode());
+        assertEquals("unsupported artifact store mode", error.getMessage());
+        assertEquals(ArtifactStoreProperties.MODE_FILESYSTEM, properties.getMode());
+    }
+
+    @Test
+    void setModeRejectsNulCorruptedKnownMode() {
+        ArtifactStoreProperties properties = new ArtifactStoreProperties();
+
+        assertThrows(
+                IllegalArgumentException.class,
+                () -> properties.setMode("file\u0000system")
+        );
+
+        assertEquals(ArtifactStoreProperties.MODE_FILESYSTEM, properties.getMode());
     }
 
     @Test