Add Origin header validation

- Fixes #695
- Does not implement Host header validation yet

Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/DefaultServerTransportSecurityValidator.java

@@ -0,0 +1,132 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.server.transport;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import io.modelcontextprotocol.util.Assert;
+
+/**
+ * Default implementation of {@link ServerTransportSecurityValidator} that validates the
+ * Origin header against a list of allowed origins.
+ *
+ * <p>
+ * Supports exact matches and wildcard port patterns (e.g., "http://example.com:*").
+ *
+ * @author Daniel Garnier-Moiroux
+ * @see ServerTransportSecurityValidator
+ * @see ServerTransportSecurityException
+ */
+public class DefaultServerTransportSecurityValidator implements ServerTransportSecurityValidator {
+
+	private static final String ORIGIN_HEADER = "Origin";
+
+	private static final ServerTransportSecurityException INVALID_ORIGIN = new ServerTransportSecurityException(403,
+			"Invalid Origin header");
+
+	private final List<String> allowedOrigins;
+
+	/**
+	 * Creates a new validator with the specified allowed origins.
+	 * @param allowedOrigins List of allowed origin patterns. Supports exact matches
+	 * (e.g., "http://example.com:8080") and wildcard ports (e.g., "http://example.com:*")
+	 */
+	public DefaultServerTransportSecurityValidator(List<String> allowedOrigins) {
+		Assert.notNull(allowedOrigins, "allowedOrigins must not be null");
+		this.allowedOrigins = allowedOrigins;
+	}
+
+	@Override
+	public void validateHeaders(Map<String, List<String>> headers) throws ServerTransportSecurityException {
+		for (Map.Entry<String, List<String>> entry : headers.entrySet()) {
+			if (ORIGIN_HEADER.equalsIgnoreCase(entry.getKey())) {
+				List<String> values = entry.getValue();
+				if (values != null && !values.isEmpty()) {
+					validateOrigin(values.get(0));
+				}
+				break;
+			}
+		}
+	}
+
+	/**
+	 * Validates a single origin value against the allowed origins. Subclasses can
+	 * override this method to customize origin validation logic.
+	 * @param origin The origin header value, or null if not present
+	 * @throws ServerTransportSecurityException if the origin is not allowed
+	 */
+	protected void validateOrigin(String origin) throws ServerTransportSecurityException {
+		// Origin absent = no validation needed (same-origin request)
+		if (origin == null || origin.isBlank()) {
+			return;
+		}
+
+		for (String allowed : allowedOrigins) {
+			if (allowed.equals(origin)) {
+				return;
+			}
+			else if (allowed.endsWith(":*")) {
+				// Wildcard port pattern: "http://example.com:*"
+				String baseOrigin = allowed.substring(0, allowed.length() - 2);
+				if (origin.equals(baseOrigin) || origin.startsWith(baseOrigin + ":")) {
+					return;
+				}
+			}
+
+		}
+
+		throw INVALID_ORIGIN;
+	}
+
+	/**
+	 * Creates a new builder for constructing a DefaultServerTransportSecurityValidator.
+	 * @return A new builder instance
+	 */
+	public static Builder builder() {
+		return new Builder();
+	}
+
+	/**
+	 * Builder for creating instances of {@link DefaultServerTransportSecurityValidator}.
+	 */
+	public static class Builder {
+
+		private final List<String> allowedOrigins = new ArrayList<>();
+
+		/**
+		 * Adds an allowed origin pattern.
+		 * @param origin The origin to allow (e.g., "http://localhost:8080" or
+		 * "http://example.com:*")
+		 * @return this builder instance
+		 */
+		public Builder allowedOrigin(String origin) {
+			this.allowedOrigins.add(origin);
+			return this;
+		}
+
+		/**
+		 * Adds multiple allowed origin patterns.
+		 * @param origins The origins to allow
+		 * @return this builder instance
+		 */
+		public Builder allowedOrigins(List<String> origins) {
+			Assert.notNull(origins, "origins must not be null");
+			this.allowedOrigins.addAll(origins);
+			return this;
+		}
+
+		/**
+		 * Builds the validator instance.
+		 * @return A new DefaultServerTransportSecurityValidator
+		 */
+		public DefaultServerTransportSecurityValidator build() {
+			return new DefaultServerTransportSecurityValidator(allowedOrigins);
+		}
+
+	}
+
+}

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletSseServerTransportProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 - 2024 the original author or authors.
+ * Copyright 2024 - 2026 the original author or authors.
  */
 
 package io.modelcontextprotocol.server.transport;
@@ -8,6 +8,9 @@ import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.time.Duration;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.UUID;
@@ -142,6 +145,11 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 	 */
 	private KeepAliveScheduler keepAliveScheduler;
 
+	/**
+	 * Security validator for validating HTTP requests.
+	 */
+	private final ServerTransportSecurityValidator securityValidator;
+
 	/**
 	 * Creates a new HttpServletSseServerTransportProvider instance with a custom SSE
 	 * endpoint.
@@ -153,23 +161,25 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 	 * @param keepAliveInterval The interval for keep-alive pings, or null to disable
 	 * keep-alive functionality
 	 * @param contextExtractor The extractor for transport context from the request.
-	 * @deprecated Use the builder {@link #builder()} instead for better configuration
-	 * options.
+	 * @param securityValidator The security validator for validating HTTP requests.
 	 */
 	private HttpServletSseServerTransportProvider(McpJsonMapper jsonMapper, String baseUrl, String messageEndpoint,
 			String sseEndpoint, Duration keepAliveInterval,
-			McpTransportContextExtractor<HttpServletRequest> contextExtractor) {
+			McpTransportContextExtractor<HttpServletRequest> contextExtractor,
+			ServerTransportSecurityValidator securityValidator) {
 
 		Assert.notNull(jsonMapper, "JsonMapper must not be null");
 		Assert.notNull(messageEndpoint, "messageEndpoint must not be null");
 		Assert.notNull(sseEndpoint, "sseEndpoint must not be null");
 		Assert.notNull(contextExtractor, "Context extractor must not be null");
+		Assert.notNull(securityValidator, "Security validator must not be null");
 
 		this.jsonMapper = jsonMapper;
 		this.baseUrl = baseUrl;
 		this.messageEndpoint = messageEndpoint;
 		this.sseEndpoint = sseEndpoint;
 		this.contextExtractor = contextExtractor;
+		this.securityValidator = securityValidator;
 
 		if (keepAliveInterval != null) {
 
@@ -246,6 +256,15 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 			return;
 		}
 
+		try {
+			Map<String, List<String>> headers = extractHeaders(request);
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			response.sendError(e.getStatusCode(), e.getMessage());
+			return;
+		}
+
 		response.setContentType("text/event-stream");
 		response.setCharacterEncoding(UTF_8);
 		response.setHeader("Cache-Control", "no-cache");
@@ -311,6 +330,15 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 			return;
 		}
 
+		try {
+			Map<String, List<String>> headers = extractHeaders(request);
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			response.sendError(e.getStatusCode(), e.getMessage());
+			return;
+		}
+
 		// Get the session ID from the request parameter
 		String sessionId = request.getParameter("sessionId");
 		if (sessionId == null) {
@@ -411,6 +439,21 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 		}
 	}
 
+	/**
+	 * Extracts all headers from the HTTP servlet request into a map.
+	 * @param request The HTTP servlet request
+	 * @return A map of header names to their values
+	 */
+	private Map<String, List<String>> extractHeaders(HttpServletRequest request) {
+		Map<String, List<String>> headers = new HashMap<>();
+		Enumeration<String> names = request.getHeaderNames();
+		while (names.hasMoreElements()) {
+			String name = names.nextElement();
+			headers.put(name, Collections.list(request.getHeaders(name)));
+		}
+		return headers;
+	}
+
 	/**
 	 * Cleans up resources when the servlet is being destroyed.
 	 * <p>
@@ -547,6 +590,8 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 
 		private Duration keepAliveInterval;
 
+		private ServerTransportSecurityValidator securityValidator = ServerTransportSecurityValidator.NOOP;
+
 		/**
 		 * Sets the JsonMapper implementation to use for serialization/deserialization. If
 		 * not specified, a JacksonJsonMapper will be created from the configured
@@ -621,6 +666,18 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 			return this;
 		}
 
+		/**
+		 * Sets the security validator for validating HTTP requests.
+		 * @param securityValidator The security validator to use. Must not be null.
+		 * @return This builder instance
+		 * @throws IllegalArgumentException if securityValidator is null
+		 */
+		public Builder securityValidator(ServerTransportSecurityValidator securityValidator) {
+			Assert.notNull(securityValidator, "Security validator must not be null");
+			this.securityValidator = securityValidator;
+			return this;
+		}
+
 		/**
 		 * Builds a new instance of HttpServletSseServerTransportProvider with the
 		 * configured settings.
@@ -633,7 +690,7 @@ public class HttpServletSseServerTransportProvider extends HttpServlet implement
 			}
 			return new HttpServletSseServerTransportProvider(
 					jsonMapper == null ? McpJsonMapper.getDefault() : jsonMapper, baseUrl, messageEndpoint, sseEndpoint,
-					keepAliveInterval, contextExtractor);
+					keepAliveInterval, contextExtractor, securityValidator);
 		}
 
 	}

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStatelessServerTransport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024-2024 the original author or authors.
+ * Copyright 2024-2026 the original author or authors.
  */
 
 package io.modelcontextprotocol.server.transport;
@@ -7,6 +7,11 @@ package io.modelcontextprotocol.server.transport;
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -58,15 +63,23 @@ public class HttpServletStatelessServerTransport extends HttpServlet implements
 
 	private volatile boolean isClosing = false;
 
+	/**
+	 * Security validator for validating HTTP requests.
+	 */
+	private final ServerTransportSecurityValidator securityValidator;
+
 	private HttpServletStatelessServerTransport(McpJsonMapper jsonMapper, String mcpEndpoint,
-			McpTransportContextExtractor<HttpServletRequest> contextExtractor) {
+			McpTransportContextExtractor<HttpServletRequest> contextExtractor,
+			ServerTransportSecurityValidator securityValidator) {
 		Assert.notNull(jsonMapper, "jsonMapper must not be null");
 		Assert.notNull(mcpEndpoint, "mcpEndpoint must not be null");
 		Assert.notNull(contextExtractor, "contextExtractor must not be null");
+		Assert.notNull(securityValidator, "Security validator must not be null");
 
 		this.jsonMapper = jsonMapper;
 		this.mcpEndpoint = mcpEndpoint;
 		this.contextExtractor = contextExtractor;
+		this.securityValidator = securityValidator;
 	}
 
 	@Override
@@ -122,6 +135,15 @@ public class HttpServletStatelessServerTransport extends HttpServlet implements
 			return;
 		}
 
+		try {
+			Map<String, List<String>> headers = extractHeaders(request);
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			response.sendError(e.getStatusCode(), e.getMessage());
+			return;
+		}
+
 		McpTransportContext transportContext = this.contextExtractor.extract(request);
 
 		String accept = request.getHeader(ACCEPT);
@@ -209,6 +231,21 @@ public class HttpServletStatelessServerTransport extends HttpServlet implements
 		writer.flush();
 	}
 
+	/**
+	 * Extracts all headers from the HTTP servlet request into a map.
+	 * @param request The HTTP servlet request
+	 * @return A map of header names to their values
+	 */
+	private Map<String, List<String>> extractHeaders(HttpServletRequest request) {
+		Map<String, List<String>> headers = new HashMap<>();
+		Enumeration<String> names = request.getHeaderNames();
+		while (names.hasMoreElements()) {
+			String name = names.nextElement();
+			headers.put(name, Collections.list(request.getHeaders(name)));
+		}
+		return headers;
+	}
+
 	/**
 	 * Cleans up resources when the servlet is being destroyed.
 	 * <p>
@@ -243,6 +280,8 @@ public class HttpServletStatelessServerTransport extends HttpServlet implements
 		private McpTransportContextExtractor<HttpServletRequest> contextExtractor = (
 				serverRequest) -> McpTransportContext.EMPTY;
 
+		private ServerTransportSecurityValidator securityValidator = ServerTransportSecurityValidator.NOOP;
+
 		private Builder() {
 			// used by a static method
 		}
@@ -288,6 +327,18 @@ public class HttpServletStatelessServerTransport extends HttpServlet implements
 			return this;
 		}
 
+		/**
+		 * Sets the security validator for validating HTTP requests.
+		 * @param securityValidator The security validator to use. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if securityValidator is null
+		 */
+		public Builder securityValidator(ServerTransportSecurityValidator securityValidator) {
+			Assert.notNull(securityValidator, "Security validator must not be null");
+			this.securityValidator = securityValidator;
+			return this;
+		}
+
 		/**
 		 * Builds a new instance of {@link HttpServletStatelessServerTransport} with the
 		 * configured settings.
@@ -297,7 +348,7 @@ public class HttpServletStatelessServerTransport extends HttpServlet implements
 		public HttpServletStatelessServerTransport build() {
 			Assert.notNull(mcpEndpoint, "Message endpoint must be set");
 			return new HttpServletStatelessServerTransport(jsonMapper == null ? McpJsonMapper.getDefault() : jsonMapper,
-					mcpEndpoint, contextExtractor);
+					mcpEndpoint, contextExtractor, securityValidator);
 		}
 
 	}

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024-2024 the original author or authors.
+ * Copyright 2024-2026 the original author or authors.
  */
 
 package io.modelcontextprotocol.server.transport;
@@ -9,7 +9,11 @@ import java.io.IOException;
 import java.io.PrintWriter;
 import java.time.Duration;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -119,6 +123,11 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 	 */
 	private KeepAliveScheduler keepAliveScheduler;
 
+	/**
+	 * Security validator for validating HTTP requests.
+	 */
+	private final ServerTransportSecurityValidator securityValidator;
+
 	/**
 	 * Constructs a new HttpServletStreamableServerTransportProvider instance.
 	 * @param jsonMapper The JsonMapper to use for JSON serialization/deserialization of
@@ -127,19 +136,24 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 	 * messages via HTTP. This endpoint will handle GET, POST, and DELETE requests.
 	 * @param disallowDelete Whether to disallow DELETE requests on the endpoint.
 	 * @param contextExtractor The extractor for transport context from the request.
+	 * @param keepAliveInterval The interval for keep-alive pings. If null, no keep-alive
+	 * will be scheduled.
+	 * @param securityValidator The security validator for validating HTTP requests.
 	 * @throws IllegalArgumentException if any parameter is null
 	 */
 	private HttpServletStreamableServerTransportProvider(McpJsonMapper jsonMapper, String mcpEndpoint,
 			boolean disallowDelete, McpTransportContextExtractor<HttpServletRequest> contextExtractor,
-			Duration keepAliveInterval) {
+			Duration keepAliveInterval, ServerTransportSecurityValidator securityValidator) {
 		Assert.notNull(jsonMapper, "JsonMapper must not be null");
 		Assert.notNull(mcpEndpoint, "MCP endpoint must not be null");
 		Assert.notNull(contextExtractor, "Context extractor must not be null");
+		Assert.notNull(securityValidator, "Security validator must not be null");
 
 		this.jsonMapper = jsonMapper;
 		this.mcpEndpoint = mcpEndpoint;
 		this.disallowDelete = disallowDelete;
 		this.contextExtractor = contextExtractor;
+		this.securityValidator = securityValidator;
 
 		if (keepAliveInterval != null) {
 
@@ -246,6 +260,15 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 			return;
 		}
 
+		try {
+			Map<String, List<String>> headers = extractHeaders(request);
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			response.sendError(e.getStatusCode(), e.getMessage());
+			return;
+		}
+
 		List<String> badRequestErrors = new ArrayList<>();
 
 		String accept = request.getHeader(ACCEPT);
@@ -373,6 +396,15 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 			return;
 		}
 
+		try {
+			Map<String, List<String>> headers = extractHeaders(request);
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			response.sendError(e.getStatusCode(), e.getMessage());
+			return;
+		}
+
 		List<String> badRequestErrors = new ArrayList<>();
 
 		String accept = request.getHeader(ACCEPT);
@@ -536,6 +568,15 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 			return;
 		}
 
+		try {
+			Map<String, List<String>> headers = extractHeaders(request);
+			this.securityValidator.validateHeaders(headers);
+		}
+		catch (ServerTransportSecurityException e) {
+			response.sendError(e.getStatusCode(), e.getMessage());
+			return;
+		}
+
 		if (this.disallowDelete) {
 			response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
 			return;
@@ -586,6 +627,21 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 		return;
 	}
 
+	/**
+	 * Extracts all headers from the HTTP servlet request into a map.
+	 * @param request The HTTP servlet request
+	 * @return A map of header names to their values
+	 */
+	private Map<String, List<String>> extractHeaders(HttpServletRequest request) {
+		Map<String, List<String>> headers = new HashMap<>();
+		Enumeration<String> names = request.getHeaderNames();
+		while (names.hasMoreElements()) {
+			String name = names.nextElement();
+			headers.put(name, Collections.list(request.getHeaders(name)));
+		}
+		return headers;
+	}
+
 	/**
 	 * Sends an SSE event to a client with a specific ID.
 	 * @param writer The writer to send the event through
@@ -774,6 +830,8 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 
 		private Duration keepAliveInterval;
 
+		private ServerTransportSecurityValidator securityValidator = ServerTransportSecurityValidator.NOOP;
+
 		/**
 		 * Sets the JsonMapper to use for JSON serialization/deserialization of MCP
 		 * messages.
@@ -833,6 +891,18 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 			return this;
 		}
 
+		/**
+		 * Sets the security validator for validating HTTP requests.
+		 * @param securityValidator The security validator to use. Must not be null.
+		 * @return this builder instance
+		 * @throws IllegalArgumentException if securityValidator is null
+		 */
+		public Builder securityValidator(ServerTransportSecurityValidator securityValidator) {
+			Assert.notNull(securityValidator, "Security validator must not be null");
+			this.securityValidator = securityValidator;
+			return this;
+		}
+
 		/**
 		 * Builds a new instance of {@link HttpServletStreamableServerTransportProvider}
 		 * with the configured settings.
@@ -843,7 +913,7 @@ public class HttpServletStreamableServerTransportProvider extends HttpServlet
 			Assert.notNull(this.mcpEndpoint, "MCP endpoint must be set");
 			return new HttpServletStreamableServerTransportProvider(
 					jsonMapper == null ? McpJsonMapper.getDefault() : jsonMapper, mcpEndpoint, disallowDelete,
-					contextExtractor, keepAliveInterval);
+					contextExtractor, keepAliveInterval, securityValidator);
 		}
 
 	}

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/ServerTransportSecurityException.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.server.transport;
+
+/**
+ * Exception thrown when security validation fails for an HTTP request. Contains HTTP
+ * status code and message.
+ *
+ * @author Daniel Garnier-Moiroux
+ * @see ServerTransportSecurityValidator
+ */
+public class ServerTransportSecurityException extends Exception {
+
+	private final int statusCode;
+
+	/**
+	 * Creates a new ServerTransportSecurityException with the specified HTTP status code
+	 * and message.
+	 */
+	public ServerTransportSecurityException(int statusCode, String message) {
+		super(message);
+		this.statusCode = statusCode;
+	}
+
+	public int getStatusCode() {
+		return statusCode;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj) {
+			return true;
+		}
+		if (obj == null || getClass() != obj.getClass()) {
+			return false;
+		}
+		ServerTransportSecurityException that = (ServerTransportSecurityException) obj;
+		return statusCode == that.statusCode && java.util.Objects.equals(getMessage(), that.getMessage());
+	}
+
+	@Override
+	public int hashCode() {
+		return java.util.Objects.hash(statusCode, getMessage());
+	}
+
+}

mcp-core/src/main/java/io/modelcontextprotocol/server/transport/ServerTransportSecurityValidator.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2026-2026 the original author or authors.
+ */
+
+package io.modelcontextprotocol.server.transport;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Interface for validating HTTP requests in server transports. Implementations can
+ * validate Origin headers, Host headers, or any other security-related headers according
+ * to the MCP specification.
+ *
+ * @author Daniel Garnier-Moiroux
+ * @see DefaultServerTransportSecurityValidator
+ * @see ServerTransportSecurityException
+ */
+@FunctionalInterface
+public interface ServerTransportSecurityValidator {
+
+	/**
+	 * A no-op validator that accepts all requests without validation.
+	 */
+	ServerTransportSecurityValidator NOOP = headers -> {
+	};
+
+	/**
+	 * Validates the HTTP headers from an incoming request.
+	 * @param headers A map of header names to their values (multi-valued headers
+	 * supported)
+	 * @throws ServerTransportSecurityException if validation fails
+	 */
+	void validateHeaders(Map<String, List<String>> headers) throws ServerTransportSecurityException;
+
+}