Add CORS support for Private Network Access

This commit adds CORS support for Private Network Access
by adding an Access-Control-Allow-Private-Network response
header when the preflight request is sent with an
Access-Control-Request-Private-Network header and that
Private Network Access has been enabled in the CORS
configuration.

See https://developer.chrome.com/blog/private-network-access-preflight/
for more details.

Closes gh-31974

(cherry picked from commit 318d460256)

spring-web/src/main/java/org/springframework/web/bind/annotation/CrossOrigin.java

@@ -133,6 +133,14 @@ public @interface CrossOrigin {
 	 */
 	String allowCredentials() default "";
 
+	/**
+	 * Whether private network access is supported. Please, see
+	 * {@link CorsConfiguration#setAllowPrivateNetwork(Boolean)} for details.
+	 * <p>By default this is not set (i.e. private network access is not supported).
+	 * @since 6.1.3
+	 */
+	String allowPrivateNetwork() default "";
+
 	/**
 	 * The maximum age (in seconds) of the cache duration for preflight responses.
 	 * <p>This property controls the value of the {@code Access-Control-Max-Age}

spring-web/src/main/java/org/springframework/web/cors/CorsConfiguration.java

@@ -93,6 +93,9 @@ public class CorsConfiguration {
 	@Nullable
 	private Boolean allowCredentials;
 
+	@Nullable
+	private Boolean allowPrivateNetwork;
+
 	@Nullable
 	private Long maxAge;
 
@@ -117,6 +120,7 @@ public class CorsConfiguration {
 		this.allowedHeaders = other.allowedHeaders;
 		this.exposedHeaders = other.exposedHeaders;
 		this.allowCredentials = other.allowCredentials;
+		this.allowPrivateNetwork = other.allowPrivateNetwork;
 		this.maxAge = other.maxAge;
 	}
 
@@ -129,9 +133,10 @@ public class CorsConfiguration {
 	 * {@code Access-Control-Allow-Origin} response header is set either to the
 	 * matched domain value or to {@code "*"}. Keep in mind however that the
 	 * CORS spec does not allow {@code "*"} when {@link #setAllowCredentials
-	 * allowCredentials} is set to {@code true} and as of 5.3 that combination
-	 * is rejected in favor of using {@link #setAllowedOriginPatterns
-	 * allowedOriginPatterns} instead.
+	 * allowCredentials} is set to {@code true}, and does not recommend {@code "*"}
+	 * when {@link #setAllowPrivateNetwork allowPrivateNetwork} is set to {@code true}.
+	 * As a consequence, those combinations are rejected in favor of using
+	 * {@link #setAllowedOriginPatterns allowedOriginPatterns} instead.
 	 * <p>By default this is not set which means that no origins are allowed.
 	 * However, an instance of this class is often initialized further, e.g. for
 	 * {@code @CrossOrigin}, via {@link #applyPermitDefaultValues()}.
@@ -182,11 +187,13 @@ public class CorsConfiguration {
 	 * domain1.com on any port, including the default port
 	 * </ul>
 	 * <p>In contrast to {@link #setAllowedOrigins(List) allowedOrigins} which
-	 * only supports "*" and cannot be used with {@code allowCredentials}, when
-	 * an allowedOriginPattern is matched, the {@code Access-Control-Allow-Origin}
-	 * response header is set to the matched origin and not to {@code "*"} nor
-	 * to the pattern. Therefore allowedOriginPatterns can be used in combination
-	 * with {@link #setAllowCredentials} set to {@code true}.
+	 * only supports "*" and cannot be used with {@code allowCredentials} or
+	 * {@code allowPrivateNetwork}, when an {@code allowedOriginPattern} is matched,
+	 * the {@code Access-Control-Allow-Origin} response header is set to the
+	 * matched origin and not to {@code "*"} nor to the pattern.
+	 * Therefore, {@code allowedOriginPatterns} can be used in combination with
+	 * {@link #setAllowCredentials} and {@link #setAllowPrivateNetwork} set to
+	 * {@code true}
 	 * <p>By default this is not set.
 	 * @since 5.3
 	 */
@@ -418,6 +425,33 @@ public class CorsConfiguration {
 		return this.allowCredentials;
 	}
 
+	/**
+	 * Whether private network access is supported for user-agents restricting such access by default.
+	 * <p>Private network requests are requests whose target server's IP address is more private than
+	 * that from which the request initiator was fetched. For example, a request from a public website
+	 * (https://example.com) to a private website (https://router.local), or a request from a private
+	 * website to localhost.
+	 * <p>Setting this property has an impact on how {@link #setAllowedOrigins(List)
+	 * origins} and {@link #setAllowedOriginPatterns(List) originPatterns} are processed,
+	 * see related API documentation for more details.
+	 * <p>By default this is not set (i.e. private network access is not supported).
+	 * @since 6.1.3
+	 * @see <a href="https://wicg.github.io/private-network-access/">Private network access specifications</a>
+	 */
+	public void setAllowPrivateNetwork(@Nullable Boolean allowPrivateNetwork) {
+		this.allowPrivateNetwork = allowPrivateNetwork;
+	}
+
+	/**
+	 * Return the configured {@code allowPrivateNetwork} flag, or {@code null} if none.
+	 * @since 6.1.3
+	 * @see #setAllowPrivateNetwork(Boolean)
+	 */
+	@Nullable
+	public Boolean getAllowPrivateNetwork() {
+		return this.allowPrivateNetwork;
+	}
+
 	/**
 	 * Configure how long, as a duration, the response from a pre-flight request
 	 * can be cached by clients.
@@ -500,6 +534,25 @@ public class CorsConfiguration {
 		}
 	}
 
+	/**
+	 * Validate that when {@link #setAllowPrivateNetwork allowPrivateNetwork} is {@code true},
+	 * {@link #setAllowedOrigins allowedOrigins} does not contain the special
+	 * value {@code "*"} since this is insecure.
+	 * @throws IllegalArgumentException if the validation fails
+	 * @since 6.1.3
+	 */
+	public void validateAllowPrivateNetwork() {
+		if (this.allowPrivateNetwork == Boolean.TRUE &&
+				this.allowedOrigins != null && this.allowedOrigins.contains(ALL)) {
+
+			throw new IllegalArgumentException(
+					"When allowPrivateNetwork is true, allowedOrigins cannot contain the special value \"*\" " +
+							"as it is not recommended from a security perspective. " +
+							"To allow private network access to a set of origins, list them explicitly " +
+							"or consider using \"allowedOriginPatterns\" instead.");
+		}
+	}
+
 	/**
 	 * Combine the non-null properties of the supplied
 	 * {@code CorsConfiguration} with this one.
@@ -534,6 +587,10 @@ public class CorsConfiguration {
 		if (allowCredentials != null) {
 			config.setAllowCredentials(allowCredentials);
 		}
+		Boolean allowPrivateNetwork = other.getAllowPrivateNetwork();
+		if (allowPrivateNetwork != null) {
+			config.setAllowPrivateNetwork(allowPrivateNetwork);
+		}
 		Long maxAge = other.getMaxAge();
 		if (maxAge != null) {
 			config.setMaxAge(maxAge);
@@ -597,6 +654,7 @@ public class CorsConfiguration {
 		if (!ObjectUtils.isEmpty(this.allowedOrigins)) {
 			if (this.allowedOrigins.contains(ALL)) {
 				validateAllowCredentials();
+				validateAllowPrivateNetwork();
 				return ALL;
 			}
 			for (String allowedOrigin : this.allowedOrigins) {

spring-web/src/main/java/org/springframework/web/cors/DefaultCorsProcessor.java

@@ -55,6 +55,18 @@ public class DefaultCorsProcessor implements CorsProcessor {
 
 	private static final Log logger = LogFactory.getLog(DefaultCorsProcessor.class);
 
+	/**
+	 * The {@code Access-Control-Request-Private-Network} request header field name.
+	 * @see <a href="https://wicg.github.io/private-network-access/">Private Network Access specification</a>
+	 */
+	static final String ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK = "Access-Control-Request-Private-Network";
+
+	/**
+	 * The {@code Access-Control-Allow-Private-Network} response header field name.
+	 * @see <a href="https://wicg.github.io/private-network-access/">Private Network Access specification</a>
+	 */
+	static final String ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK = "Access-Control-Allow-Private-Network";
+
 
 	@Override
 	@SuppressWarnings("resource")
@@ -156,6 +168,11 @@ public class DefaultCorsProcessor implements CorsProcessor {
 			responseHeaders.setAccessControlAllowCredentials(true);
 		}
 
+		if (Boolean.TRUE.equals(config.getAllowPrivateNetwork()) &&
+				Boolean.parseBoolean(request.getHeaders().getFirst(ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK))) {
+			responseHeaders.set(ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK, Boolean.toString(true));
+		}
+
 		if (preFlightRequest && config.getMaxAge() != null) {
 			responseHeaders.setAccessControlMaxAge(config.getMaxAge());
 		}

spring-web/src/main/java/org/springframework/web/cors/reactive/DefaultCorsProcessor.java

@@ -53,6 +53,18 @@ public class DefaultCorsProcessor implements CorsProcessor {
 	private static final List<String> VARY_HEADERS = Arrays.asList(
 			HttpHeaders.ORIGIN, HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, HttpHeaders.ACCESS_CONTROL_REQUEST_HEADERS);
 
+	/**
+	 * The {@code Access-Control-Request-Private-Network} request header field name.
+	 * @see <a href="https://wicg.github.io/private-network-access/">Private Network Access specification</a>
+	 */
+	static final String ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK = "Access-Control-Request-Private-Network";
+
+	/**
+	 * The {@code Access-Control-Allow-Private-Network} response header field name.
+	 * @see <a href="https://wicg.github.io/private-network-access/">Private Network Access specification</a>
+	 */
+	static final String ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK = "Access-Control-Allow-Private-Network";
+
 
 	@Override
 	public boolean process(@Nullable CorsConfiguration config, ServerWebExchange exchange) {
@@ -155,6 +167,11 @@ public class DefaultCorsProcessor implements CorsProcessor {
 			responseHeaders.setAccessControlAllowCredentials(true);
 		}
 
+		if (Boolean.TRUE.equals(config.getAllowPrivateNetwork()) &&
+				Boolean.parseBoolean(request.getHeaders().getFirst(ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK))) {
+			responseHeaders.set(ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK, Boolean.toString(true));
+		}
+
 		if (preFlightRequest && config.getMaxAge() != null) {
 			responseHeaders.setAccessControlMaxAge(config.getMaxAge());
 		}

spring-web/src/test/java/org/springframework/web/cors/CorsConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,6 +50,8 @@ class CorsConfigurationTests {
 		assertThat(config.getExposedHeaders()).isNull();
 		config.setAllowCredentials(null);
 		assertThat(config.getAllowCredentials()).isNull();
+		config.setAllowPrivateNetwork(null);
+		assertThat(config.getAllowPrivateNetwork()).isNull();
 		config.setMaxAge((Long) null);
 		assertThat(config.getMaxAge()).isNull();
 	}
@@ -63,6 +65,7 @@ class CorsConfigurationTests {
 		config.addAllowedMethod("*");
 		config.addExposedHeader("*");
 		config.setAllowCredentials(true);
+		config.setAllowPrivateNetwork(true);
 		config.setMaxAge(123L);
 
 		assertThat(config.getAllowedOrigins()).containsExactly("*");
@@ -71,6 +74,7 @@ class CorsConfigurationTests {
 		assertThat(config.getAllowedMethods()).containsExactly("*");
 		assertThat(config.getExposedHeaders()).containsExactly("*");
 		assertThat(config.getAllowCredentials()).isTrue();
+		assertThat(config.getAllowPrivateNetwork()).isTrue();
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(123));
 	}
 
@@ -93,6 +97,7 @@ class CorsConfigurationTests {
 		config.addAllowedMethod(HttpMethod.GET.name());
 		config.setMaxAge(123L);
 		config.setAllowCredentials(true);
+		config.setAllowPrivateNetwork(true);
 
 		CorsConfiguration other = new CorsConfiguration();
 		config = config.combine(other);
@@ -105,6 +110,7 @@ class CorsConfigurationTests {
 		assertThat(config.getAllowedMethods()).containsExactly(HttpMethod.GET.name());
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(123));
 		assertThat(config.getAllowCredentials()).isTrue();
+		assertThat(config.getAllowPrivateNetwork()).isTrue();
 	}
 
 	@Test  // SPR-15772
@@ -258,6 +264,7 @@ class CorsConfigurationTests {
 		config.addAllowedMethod(HttpMethod.GET.name());
 		config.setMaxAge(123L);
 		config.setAllowCredentials(true);
+		config.setAllowPrivateNetwork(true);
 
 		CorsConfiguration other = new CorsConfiguration();
 		other.addAllowedOrigin("https://domain2.com");
@@ -267,6 +274,7 @@ class CorsConfigurationTests {
 		other.addAllowedMethod(HttpMethod.PUT.name());
 		other.setMaxAge(456L);
 		other.setAllowCredentials(false);
+		other.setAllowPrivateNetwork(false);
 
 		config = config.combine(other);
 		assertThat(config).isNotNull();
@@ -277,6 +285,7 @@ class CorsConfigurationTests {
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(456));
 		assertThat(config).isNotNull();
 		assertThat(config.getAllowCredentials()).isFalse();
+		assertThat(config.getAllowPrivateNetwork()).isFalse();
 		assertThat(config.getAllowedOriginPatterns()).containsExactly("http://*.domain1.com", "http://*.domain2.com");
 	}
 

spring-web/src/test/java/org/springframework/web/cors/DefaultCorsProcessorTests.java

@@ -352,6 +352,32 @@ public class DefaultCorsProcessorTests {
 		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
 	}
 
+	@Test
+	public void preflightRequestPrivateNetworkWithWildcardOrigin() throws Exception {
+		this.request.setMethod(HttpMethod.OPTIONS.name());
+		this.request.addHeader(HttpHeaders.ORIGIN, "https://domain2.com");
+		this.request.addHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, "GET");
+		this.request.addHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_HEADERS, "Header1");
+		this.request.addHeader(DefaultCorsProcessor.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK, "true");
+		this.conf.setAllowedOrigins(Arrays.asList("https://domain1.com", "*", "http://domain3.example"));
+		this.conf.addAllowedHeader("Header1");
+		this.conf.setAllowPrivateNetwork(true);
+
+		assertThatIllegalArgumentException().isThrownBy(() ->
+				this.processor.processRequest(this.conf, this.request, this.response));
+
+		this.conf.setAllowedOrigins(null);
+		this.conf.addAllowedOriginPattern("*");
+
+		this.processor.processRequest(this.conf, this.request, this.response);
+		assertThat(this.response.containsHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(this.response.containsHeader(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isTrue();
+		assertThat(this.response.getHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)).isEqualTo("https://domain2.com");
+		assertThat(this.response.getHeaders(HttpHeaders.VARY)).contains(HttpHeaders.ORIGIN,
+				HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, HttpHeaders.ACCESS_CONTROL_REQUEST_HEADERS);
+		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+	}
+
 	@Test
 	public void preflightRequestAllowedHeaders() throws Exception {
 		this.request.setMethod(HttpMethod.OPTIONS.name());
@@ -435,4 +461,49 @@ public class DefaultCorsProcessorTests {
 				HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, HttpHeaders.ACCESS_CONTROL_REQUEST_HEADERS);
 	}
 
+	@Test
+	public void preflightRequestWithoutAccessControlRequestPrivateNetwork() throws Exception {
+		this.request.setMethod(HttpMethod.OPTIONS.name());
+		this.request.addHeader(HttpHeaders.ORIGIN, "https://domain2.com");
+		this.request.addHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, "GET");
+		this.conf.addAllowedHeader("*");
+		this.conf.addAllowedOrigin("https://domain2.com");
+
+		this.processor.processRequest(this.conf, this.request, this.response);
+		assertThat(this.response.containsHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(this.response.containsHeader(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isFalse();
+		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+	}
+
+	@Test
+	public void preflightRequestWithAccessControlRequestPrivateNetworkNotAllowed() throws Exception {
+		this.request.setMethod(HttpMethod.OPTIONS.name());
+		this.request.addHeader(HttpHeaders.ORIGIN, "https://domain2.com");
+		this.request.addHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, "GET");
+		this.request.addHeader(DefaultCorsProcessor.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK, "true");
+		this.conf.addAllowedHeader("*");
+		this.conf.addAllowedOrigin("https://domain2.com");
+
+		this.processor.processRequest(this.conf, this.request, this.response);
+		assertThat(this.response.containsHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(this.response.containsHeader(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isFalse();
+		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+	}
+
+	@Test
+	public void preflightRequestWithAccessControlRequestPrivateNetworkAllowed() throws Exception {
+		this.request.setMethod(HttpMethod.OPTIONS.name());
+		this.request.addHeader(HttpHeaders.ORIGIN, "https://domain2.com");
+		this.request.addHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, "GET");
+		this.request.addHeader(DefaultCorsProcessor.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK, "true");
+		this.conf.addAllowedHeader("*");
+		this.conf.addAllowedOrigin("https://domain2.com");
+		this.conf.setAllowPrivateNetwork(true);
+
+		this.processor.processRequest(this.conf, this.request, this.response);
+		assertThat(this.response.containsHeader(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(this.response.containsHeader(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isTrue();
+		assertThat(this.response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+	}
+
 }

spring-web/src/test/java/org/springframework/web/cors/reactive/DefaultCorsProcessorTests.java

@@ -364,6 +364,33 @@ public class DefaultCorsProcessorTests {
 		assertThat((Object) response.getStatusCode()).isNull();
 	}
 
+	@Test
+	public void preflightRequestPrivateNetworkWithWildcardOrigin() {
+		ServerWebExchange exchange = MockServerWebExchange.from(preFlightRequest()
+				.header(ACCESS_CONTROL_REQUEST_METHOD, "GET")
+				.header(ACCESS_CONTROL_REQUEST_HEADERS, "Header1")
+				.header(DefaultCorsProcessor.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK, "true"));
+
+		this.conf.addAllowedOrigin("https://domain1.com");
+		this.conf.addAllowedOrigin("*");
+		this.conf.addAllowedOrigin("http://domain3.example");
+		this.conf.addAllowedHeader("Header1");
+		this.conf.setAllowPrivateNetwork(true);
+		assertThatIllegalArgumentException().isThrownBy(() -> this.processor.process(this.conf, exchange));
+
+		this.conf.setAllowedOrigins(null);
+		this.conf.addAllowedOriginPattern("*");
+		this.processor.process(this.conf, exchange);
+
+		ServerHttpResponse response = exchange.getResponse();
+		assertThat(response.getHeaders().containsKey(ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(response.getHeaders().containsKey(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isTrue();
+		assertThat(response.getHeaders().getFirst(ACCESS_CONTROL_ALLOW_ORIGIN)).isEqualTo("https://domain2.com");
+		assertThat(response.getHeaders().get(VARY)).contains(ORIGIN,
+				ACCESS_CONTROL_REQUEST_METHOD, ACCESS_CONTROL_REQUEST_HEADERS);
+		assertThat(response.getStatusCode()).isNull();
+	}
+
 	@Test
 	public void preflightRequestAllowedHeaders() {
 		ServerWebExchange exchange = MockServerWebExchange.from(preFlightRequest()
@@ -460,6 +487,57 @@ public class DefaultCorsProcessorTests {
 				ACCESS_CONTROL_REQUEST_METHOD, ACCESS_CONTROL_REQUEST_HEADERS);
 	}
 
+	@Test
+	public void preflightRequestWithoutAccessControlRequestPrivateNetwork() {
+		ServerWebExchange exchange = MockServerWebExchange.from(preFlightRequest()
+				.header(ACCESS_CONTROL_REQUEST_METHOD, "GET"));
+
+		this.conf.addAllowedHeader("*");
+		this.conf.addAllowedOrigin("https://domain2.com");
+
+		this.processor.process(this.conf, exchange);
+
+		ServerHttpResponse response = exchange.getResponse();
+		assertThat(response.getHeaders().containsKey(ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(response.getHeaders().containsKey(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isFalse();
+		assertThat(response.getStatusCode()).isNull();
+	}
+
+	@Test
+	public void preflightRequestWithAccessControlRequestPrivateNetworkNotAllowed() {
+		ServerWebExchange exchange = MockServerWebExchange.from(preFlightRequest()
+				.header(ACCESS_CONTROL_REQUEST_METHOD, "GET")
+				.header(DefaultCorsProcessor.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK, "true"));
+
+		this.conf.addAllowedHeader("*");
+		this.conf.addAllowedOrigin("https://domain2.com");
+
+		this.processor.process(this.conf, exchange);
+
+		ServerHttpResponse response = exchange.getResponse();
+		assertThat(response.getHeaders().containsKey(ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(response.getHeaders().containsKey(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isFalse();
+		assertThat(response.getStatusCode()).isNull();
+	}
+
+	@Test
+	public void preflightRequestWithAccessControlRequestPrivateNetworkAllowed() {
+		ServerWebExchange exchange = MockServerWebExchange.from(preFlightRequest()
+				.header(ACCESS_CONTROL_REQUEST_METHOD, "GET")
+				.header(DefaultCorsProcessor.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK, "true"));
+
+		this.conf.addAllowedHeader("*");
+		this.conf.addAllowedOrigin("https://domain2.com");
+		this.conf.setAllowPrivateNetwork(true);
+
+		this.processor.process(this.conf, exchange);
+
+		ServerHttpResponse response = exchange.getResponse();
+		assertThat(response.getHeaders().containsKey(ACCESS_CONTROL_ALLOW_ORIGIN)).isTrue();
+		assertThat(response.getHeaders().containsKey(DefaultCorsProcessor.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK)).isTrue();
+		assertThat(response.getStatusCode()).isNull();
+	}
+
 
 	private ServerWebExchange actualRequest() {
 		return MockServerWebExchange.from(corsRequest(HttpMethod.GET));

spring-webflux/src/main/java/org/springframework/web/reactive/config/CorsRegistration.java

@@ -131,6 +131,17 @@ public class CorsRegistration {
 		return this;
 	}
 
+	/**
+	 * Whether private network access is supported.
+	 * <p>Please, see {@link CorsConfiguration#setAllowPrivateNetwork(Boolean)} for details.
+	 * <p>By default this is not set (i.e. private network access is not supported).
+	 * @since 6.1.3
+	 */
+	public CorsRegistration allowPrivateNetwork(boolean allowPrivateNetwork) {
+		this.config.setAllowPrivateNetwork(allowPrivateNetwork);
+		return this;
+	}
+
 	/**
 	 * Configure how long in seconds the response from a pre-flight request
 	 * can be cached by clients.

spring-webflux/src/main/java/org/springframework/web/reactive/handler/AbstractHandlerMapping.java

@@ -196,6 +196,7 @@ public abstract class AbstractHandlerMapping extends ApplicationObjectSupport
 				config = (config != null ? config.combine(handlerConfig) : handlerConfig);
 				if (config != null) {
 					config.validateAllowCredentials();
+					config.validateAllowPrivateNetwork();
 				}
 				if (!this.corsProcessor.process(config, exchange) || CorsUtils.isPreFlightRequest(request)) {
 					return NO_OP_HANDLER;

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/AbstractHandlerMethodMapping.java

@@ -534,6 +534,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 				CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
 				if (corsConfig != null) {
 					corsConfig.validateAllowCredentials();
+					corsConfig.validateAllowPrivateNetwork();
 					this.corsLookup.put(handlerMethod, corsConfig);
 				}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/RequestMappingHandlerMapping.java

@@ -341,6 +341,18 @@ public class RequestMappingHandlerMapping extends RequestMappingInfoHandlerMappi
 					"or an empty string (\"\"): current value is [" + allowCredentials + "]");
 		}
 
+		String allowPrivateNetwork = resolveCorsAnnotationValue(annotation.allowPrivateNetwork());
+		if ("true".equalsIgnoreCase(allowPrivateNetwork)) {
+			config.setAllowPrivateNetwork(true);
+		}
+		else if ("false".equalsIgnoreCase(allowPrivateNetwork)) {
+			config.setAllowPrivateNetwork(false);
+		}
+		else if (!allowPrivateNetwork.isEmpty()) {
+			throw new IllegalStateException("@CrossOrigin's allowPrivateNetwork value must be \"true\", \"false\", " +
+					"or an empty string (\"\"): current value is [" + allowPrivateNetwork + "]");
+		}
+
 		if (annotation.maxAge() >= 0) {
 			config.setMaxAge(annotation.maxAge());
 		}

spring-webflux/src/test/java/org/springframework/web/reactive/config/CorsRegistryTests.java

@@ -51,8 +51,8 @@ public class CorsRegistryTests {
 	@Test
 	public void customizedMapping() {
 		this.registry.addMapping("/foo").allowedOrigins("https://domain2.com", "https://domain2.com")
-				.allowedMethods("DELETE").allowCredentials(false).allowedHeaders("header1", "header2")
-				.exposedHeaders("header3", "header4").maxAge(3600);
+				.allowedMethods("DELETE").allowCredentials(true).allowPrivateNetwork(true)
+				.allowedHeaders("header1", "header2").exposedHeaders("header3", "header4").maxAge(3600);
 		Map<String, CorsConfiguration> configs = this.registry.getCorsConfigurations();
 		assertThat(configs.size()).isEqualTo(1);
 		CorsConfiguration config = configs.get("/foo");
@@ -60,7 +60,8 @@ public class CorsRegistryTests {
 		assertThat(config.getAllowedMethods()).isEqualTo(Collections.singletonList("DELETE"));
 		assertThat(config.getAllowedHeaders()).isEqualTo(Arrays.asList("header1", "header2"));
 		assertThat(config.getExposedHeaders()).isEqualTo(Arrays.asList("header3", "header4"));
-		assertThat(config.getAllowCredentials()).isFalse();
+		assertThat(config.getAllowCredentials()).isTrue();
+		assertThat(config.getAllowPrivateNetwork()).isTrue();
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(3600));
 	}
 
@@ -90,6 +91,7 @@ public class CorsRegistryTests {
 		assertThat(config.getAllowedHeaders()).isEqualTo(Collections.singletonList("*"));
 		assertThat(config.getExposedHeaders()).isEmpty();
 		assertThat(config.getAllowCredentials()).isNull();
+		assertThat(config.getAllowPrivateNetwork()).isNull();
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(1800));
 	}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/config/CorsBeanDefinitionParser.java

@@ -84,6 +84,7 @@ public class CorsBeanDefinitionParser implements BeanDefinitionParser {
 				}
 				config.applyPermitDefaultValues();
 				config.validateAllowCredentials();
+				config.validateAllowPrivateNetwork();
 				corsConfigurations.put(mapping.getAttribute("path"), config);
 			}
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/CorsRegistration.java

@@ -132,6 +132,17 @@ public class CorsRegistration {
 		return this;
 	}
 
+	/**
+	 * Whether private network access is supported.
+	 * <p>By default this is not set (i.e. private network access is not supported).
+	 * @since 6.1.3
+	 * @see <a href="https://wicg.github.io/private-network-access/">Private network access specifications</a>
+	 */
+	public CorsRegistration allowPrivateNetwork(boolean allowPrivateNetwork) {
+		this.config.setAllowPrivateNetwork(allowPrivateNetwork);
+		return this;
+	}
+
 	/**
 	 * Configure how long in seconds the response from a pre-flight request
 	 * can be cached by clients.

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerMapping.java

@@ -530,6 +530,7 @@ public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport
 			}
 			if (config != null) {
 				config.validateAllowCredentials();
+				config.validateAllowPrivateNetwork();
 			}
 			executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerMethodMapping.java

@@ -648,6 +648,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 				CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
 				if (corsConfig != null) {
 					corsConfig.validateAllowCredentials();
+					corsConfig.validateAllowPrivateNetwork();
 					this.corsLookup.put(handlerMethod, corsConfig);
 				}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerMapping.java

@@ -501,6 +501,18 @@ public class RequestMappingHandlerMapping extends RequestMappingInfoHandlerMappi
 					"or an empty string (\"\"): current value is [" + allowCredentials + "]");
 		}
 
+		String allowPrivateNetwork = resolveCorsAnnotationValue(annotation.allowPrivateNetwork());
+		if ("true".equalsIgnoreCase(allowPrivateNetwork)) {
+			config.setAllowPrivateNetwork(true);
+		}
+		else if ("false".equalsIgnoreCase(allowPrivateNetwork)) {
+			config.setAllowPrivateNetwork(false);
+		}
+		else if (!allowPrivateNetwork.isEmpty()) {
+			throw new IllegalStateException("@CrossOrigin's allowPrivateNetwork value must be \"true\", \"false\", " +
+					"or an empty string (\"\"): current value is [" + allowPrivateNetwork + "]");
+		}
+
 		if (annotation.maxAge() >= 0 ) {
 			config.setMaxAge(annotation.maxAge());
 		}

spring-webmvc/src/test/java/org/springframework/web/servlet/config/annotation/CorsRegistryTests.java

@@ -56,8 +56,8 @@ public class CorsRegistryTests {
 	@Test
 	public void customizedMapping() {
 		this.registry.addMapping("/foo").allowedOrigins("https://domain2.com", "https://domain2.com")
-				.allowedMethods("DELETE").allowCredentials(false).allowedHeaders("header1", "header2")
-				.exposedHeaders("header3", "header4").maxAge(3600);
+				.allowedMethods("DELETE").allowCredentials(true).allowPrivateNetwork(true)
+				.allowedHeaders("header1", "header2").exposedHeaders("header3", "header4").maxAge(3600);
 		Map<String, CorsConfiguration> configs = this.registry.getCorsConfigurations();
 		assertThat(configs.size()).isEqualTo(1);
 		CorsConfiguration config = configs.get("/foo");
@@ -65,7 +65,8 @@ public class CorsRegistryTests {
 		assertThat(config.getAllowedMethods()).isEqualTo(Collections.singletonList("DELETE"));
 		assertThat(config.getAllowedHeaders()).isEqualTo(Arrays.asList("header1", "header2"));
 		assertThat(config.getExposedHeaders()).isEqualTo(Arrays.asList("header3", "header4"));
-		assertThat(config.getAllowCredentials()).isFalse();
+		assertThat(config.getAllowCredentials()).isTrue();
+		assertThat(config.getAllowPrivateNetwork()).isTrue();
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(3600));
 	}
 
@@ -95,6 +96,7 @@ public class CorsRegistryTests {
 		assertThat(config.getAllowedHeaders()).isEqualTo(Collections.singletonList("*"));
 		assertThat(config.getExposedHeaders()).isEmpty();
 		assertThat(config.getAllowCredentials()).isNull();
+		assertThat(config.getAllowPrivateNetwork()).isNull();
 		assertThat(config.getMaxAge()).isEqualTo(Long.valueOf(1800));
 	}
 }