diff --git a/classes/Visualizer/Module.php b/classes/Visualizer/Module.php
index 99ac4a79..13d7cbfc 100644
--- a/classes/Visualizer/Module.php
+++ b/classes/Visualizer/Module.php
@@ -812,7 +812,36 @@ public static function decode_content( $content ) {
 		if ( ! is_string( $content ) ) {
 			return false;
 		}
-		return self::strip_incomplete_objects( unserialize( trim( $content ), array( 'allowed_classes' => false ) ) );
+		$value = unserialize( trim( $content ), array( 'allowed_classes' => false ) );
+		if ( self::contains_references( $value ) ) {
+			return false;
+		}
+		return self::strip_incomplete_objects( $value );
+	}
+
+	/**
+	 * Check decoded arrays for references before recursively processing them.
+	 *
+	 * Cyclic serialized arrays necessarily contain a reference. Rejecting all
+	 * references also prevents shared references from becoming cycles later,
+	 * so strip_incomplete_objects() cannot recurse without terminating.
+	 *
+	 * @param mixed $value The decoded value.
+	 * @return bool Whether the value contains an array reference.
+	 */
+	private static function contains_references( $value ) {
+		if ( ! is_array( $value ) ) {
+			return false;
+		}
+		foreach ( array_keys( $value ) as $key ) {
+			if ( null !== ReflectionReference::fromArrayElement( $value, $key ) ) {
+				return true;
+			}
+			if ( is_array( $value[ $key ] ) && self::contains_references( $value[ $key ] ) ) {
+				return true;
+			}
+		}
+		return false;
 	}
 
 	/**
diff --git a/tests/test-security-object-injection.php b/tests/test-security-object-injection.php
index 15fdf9f6..d69ad917 100644
--- a/tests/test-security-object-injection.php
+++ b/tests/test-security-object-injection.php
@@ -113,6 +113,25 @@ public function test_decode_content_does_not_instantiate_objects() {
 		);
 	}
 
+	/**
+	 * The shared decoder must reject cyclic serialized arrays without recursing.
+	 *
+	 * The allowed_classes guard only blocks objects; a self-referential array
+	 * (R:/r: token) survives it and would drive strip_incomplete_objects() into
+	 * unbounded recursion. decode_content() must reject it up front.
+	 */
+	public function test_decode_content_rejects_cyclic_arrays() {
+		$this->assertFalse(
+			Visualizer_Module::decode_content( 'a:1:{i:0;R:1;}' ),
+			'decode_content() must reject cyclic arrays.'
+		);
+		$this->assertSame(
+			array( 'marker' => 'R:1;' ),
+			Visualizer_Module::decode_content( serialize( array( 'marker' => 'R:1;' ) ) ),
+			'Reference-like text inside strings must remain valid.'
+		);
+	}
+
 	/**
 	 * The Utility pie/polarArea render palette call site must not instantiate objects.
 	 *