diff --git a/framework-platform/framework-platform.gradle b/framework-platform/framework-platform.gradle
index 9041a5d8f50..5775ab20714 100644
--- a/framework-platform/framework-platform.gradle
+++ b/framework-platform/framework-platform.gradle
@@ -138,7 +138,6 @@ dependencies {
 		api("org.seleniumhq.selenium:selenium-java:4.41.0")
 		api("org.skyscreamer:jsonassert:1.5.3")
 		api("org.testng:testng:7.12.0")
-		api("org.webjars:underscorejs:1.8.3")
 		api("org.webjars:webjars-locator-lite:1.1.0")
 		api("org.xmlunit:xmlunit-assertj:2.10.4")
 		api("org.xmlunit:xmlunit-matchers:2.10.4")
diff --git a/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java b/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java
index 1b9b668ba0d..24add7f4f3d 100644
--- a/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java
+++ b/spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java
@@ -238,7 +238,7 @@ public abstract class MimeTypeUtils {
 						break;
 					}
 				}
-				else if (ch == '"') {
+				else if (ch == '"' && mimeType.charAt(nextIndex - 1) != '\\') {
 					quoted = !quoted;
 				}
 				nextIndex++;
diff --git a/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java b/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java
index b1998ca0795..6346b8ec540 100644
--- a/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java
+++ b/spring-core/src/test/java/org/springframework/util/MimeTypeTests.java
@@ -98,7 +98,7 @@ class MimeTypeTests {
 	}
 
 	@Test
-	void parseQuotedSeparator() {
+	void parseQuotedParameterValue() {
 		String s = "application/xop+xml;charset=utf-8;type=\"application/soap+xml;action=\\\"https://x.y.z\\\"\"";
 		MimeType mimeType = MimeType.valueOf(s);
 		assertThat(mimeType.getType()).as("Invalid type").isEqualTo("application");
@@ -107,6 +107,15 @@ class MimeTypeTests {
 		assertThat(mimeType.getParameter("type")).isEqualTo("\"application/soap+xml;action=\\\"https://x.y.z\\\"\"");
 	}
 
+	@Test
+	void parseParameterWithQuotedPair() {
+		String s = "text/plain;twelve=\"1\\\"2\"";
+		MimeType mimeType = MimeType.valueOf(s);
+		assertThat(mimeType.getType()).as("Invalid type").isEqualTo("text");
+		assertThat(mimeType.getSubtype()).as("Invalid subtype").isEqualTo("plain");
+		assertThat(mimeType.getParameter("twelve")).isEqualTo("\"1\\\"2\"");
+	}
+
 	@Test
 	void withConversionService() {
 		ConversionService conversionService = new DefaultConversionService();
diff --git a/spring-web/src/main/java/org/springframework/web/server/WebSession.java b/spring-web/src/main/java/org/springframework/web/server/WebSession.java
index a1c823393f9..3142dbf4873 100644
--- a/spring-web/src/main/java/org/springframework/web/server/WebSession.java
+++ b/spring-web/src/main/java/org/springframework/web/server/WebSession.java
@@ -100,20 +100,6 @@ public interface WebSession {
 	 */
 	boolean isStarted();
 
-	/**
-	 * Generate a new id for the session and update the underlying session
-	 * storage to reflect the new id. After a successful call {@link #getId()}
-	 * reflects the new session id.
-	 * @return completion notification (success or error)
-	 */
-	Mono<Void> changeSessionId();
-
-	/**
-	 * Invalidate the current session and clear session storage.
-	 * @return completion notification (success or error)
-	 */
-	Mono<Void> invalidate();
-
 	/**
 	 * Save the session through the {@code WebSessionStore} as follows:
 	 * <ul>
@@ -131,6 +117,20 @@ public interface WebSession {
 	 */
 	Mono<Void> save();
 
+	/**
+	 * Generate a new id for the session and update the underlying session
+	 * storage to reflect the new id. After a successful call {@link #getId()}
+	 * reflects the new session id.
+	 * @return completion notification (success or error)
+	 */
+	Mono<Void> changeSessionId();
+
+	/**
+	 * Invalidate the current session and clear session storage.
+	 * @return completion notification (success or error)
+	 */
+	Mono<Void> invalidate();
+
 	/**
 	 * Return {@code true} if the session expired after {@link #getMaxIdleTime()
 	 * maxIdleTime} elapsed.
diff --git a/spring-web/src/main/java/org/springframework/web/server/session/InMemoryWebSessionStore.java b/spring-web/src/main/java/org/springframework/web/server/session/InMemoryWebSessionStore.java
index 6ec24eaacb3..9b226edadc0 100644
--- a/spring-web/src/main/java/org/springframework/web/server/session/InMemoryWebSessionStore.java
+++ b/spring-web/src/main/java/org/springframework/web/server/session/InMemoryWebSessionStore.java
@@ -207,6 +207,7 @@ public class InMemoryWebSessionStore implements WebSessionStore {
 
 		private final AtomicReference<State> state = new AtomicReference<>(State.NEW);
 
+		private final Lock lock = new ReentrantLock();
 
 		public InMemoryWebSession(Instant creationTime, Duration maxIdleTime) {
 			this.creationTime = creationTime;
@@ -256,29 +257,6 @@ public class InMemoryWebSessionStore implements WebSessionStore {
 			return this.state.get().equals(State.STARTED) || !getAttributes().isEmpty();
 		}
 
-		@Override
-		public Mono<Void> changeSessionId() {
-			return Mono.<Void>defer(() -> {
-						String currentId = this.id.get();
-						InMemoryWebSessionStore.this.sessions.remove(currentId);
-						String newId = String.valueOf(idGenerator.generateId());
-						this.id.set(newId);
-						InMemoryWebSessionStore.this.sessions.put(this.id.get(), this);
-						return Mono.empty();
-					})
-					.subscribeOn(Schedulers.boundedElastic())
-					.publishOn(Schedulers.parallel())
-					.then();
-		}
-
-		@Override
-		public Mono<Void> invalidate() {
-			this.state.set(State.EXPIRED);
-			getAttributes().clear();
-			InMemoryWebSessionStore.this.sessions.remove(this.id.get());
-			return Mono.empty();
-		}
-
 		@Override
 		@SuppressWarnings("NullAway") // Dataflow analysis limitation
 		public Mono<Void> save() {
@@ -292,11 +270,19 @@ public class InMemoryWebSessionStore implements WebSessionStore {
 
 			if (isStarted()) {
 				// Save
-				InMemoryWebSessionStore.this.sessions.put(this.id.get(), this);
+				if (InMemoryWebSessionStore.this.sessions.get(getId()) == null) {
+					this.lock.lock();
+					try {
+						InMemoryWebSessionStore.this.sessions.putIfAbsent(getId(), this);
+					}
+					finally {
+						this.lock.unlock();
+					}
+				}
 
 				// Unless it was invalidated
 				if (this.state.get().equals(State.EXPIRED)) {
-					InMemoryWebSessionStore.this.sessions.remove(this.id.get());
+					InMemoryWebSessionStore.this.sessions.remove(getId());
 					return Mono.error(new IllegalStateException("Session was invalidated"));
 				}
 			}
@@ -307,12 +293,41 @@ public class InMemoryWebSessionStore implements WebSessionStore {
 		private void checkMaxSessionsLimit() {
 			if (sessions.size() >= maxSessions) {
 				expiredSessionChecker.removeExpiredSessions(clock.instant());
-				if (sessions.size() >= maxSessions && !sessions.containsKey(this.id.get())) {
+				if (sessions.size() >= maxSessions && !sessions.containsKey(getId())) {
 					throw new IllegalStateException("Max sessions limit reached: " + sessions.size());
 				}
 			}
 		}
 
+		@Override
+		public Mono<Void> changeSessionId() {
+			return Mono.<Void>defer(() -> {
+						this.lock.lock();
+						try {
+							String oldId = getId();
+							String newId = String.valueOf(idGenerator.generateId());
+							InMemoryWebSessionStore.this.sessions.remove(oldId);
+							InMemoryWebSessionStore.this.sessions.put(newId, this);
+							this.id.set(newId);
+						}
+						finally {
+							this.lock.unlock();
+						}
+						return Mono.empty();
+					})
+					.subscribeOn(Schedulers.boundedElastic())
+					.publishOn(Schedulers.parallel())
+					.then();
+		}
+
+		@Override
+		public Mono<Void> invalidate() {
+			this.state.set(State.EXPIRED);
+			getAttributes().clear();
+			InMemoryWebSessionStore.this.sessions.remove(getId());
+			return Mono.empty();
+		}
+
 		@Override
 		public boolean isExpired() {
 			return isExpired(clock.instant());
diff --git a/spring-webflux/spring-webflux.gradle b/spring-webflux/spring-webflux.gradle
index 16c9be3a271..8de09951ee5 100644
--- a/spring-webflux/spring-webflux.gradle
+++ b/spring-webflux/spring-webflux.gradle
@@ -61,7 +61,7 @@ dependencies {
 	testRuntimeOnly("org.glassfish:jakarta.el")
 	testRuntimeOnly("org.jruby:jruby")
 	testRuntimeOnly("org.python:jython-standalone")
-	testRuntimeOnly("org.webjars:underscorejs")
+	testRuntimeOnly("org.webjars:momentjs:2.29.4")
 }
 
 test {
diff --git a/spring-webflux/src/main/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolver.java b/spring-webflux/src/main/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolver.java
index 6983d2fddfa..3fd7b40c402 100644
--- a/spring-webflux/src/main/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolver.java
+++ b/spring-webflux/src/main/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolver.java
@@ -90,7 +90,8 @@ public class LiteWebJarsResourceResolver extends AbstractResourceResolver {
 				.switchIfEmpty(Mono.defer(() -> {
 					String webJarResourcePath = findWebJarResourcePath(resourceUrlPath);
 					if (webJarResourcePath != null) {
-						return chain.resolveUrlPath(webJarResourcePath, locations);
+						Mono<String> fallback = (webJarResourcePath.endsWith("/")) ? Mono.just(webJarResourcePath) : Mono.empty();
+						return chain.resolveUrlPath(webJarResourcePath, locations).switchIfEmpty(fallback);
 					}
 					else {
 						return Mono.empty();
diff --git a/spring-webflux/src/test/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolverTests.java b/spring-webflux/src/test/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolverTests.java
index e7a5ce16cff..fe8d35f87c9 100644
--- a/spring-webflux/src/test/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolverTests.java
+++ b/spring-webflux/src/test/java/org/springframework/web/reactive/resource/LiteWebJarsResourceResolverTests.java
@@ -29,6 +29,8 @@ import org.springframework.web.testfixture.http.server.reactive.MockServerHttpRe
 import org.springframework.web.testfixture.server.MockServerWebExchange;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
@@ -80,8 +82,8 @@ class LiteWebJarsResourceResolverTests {
 
 	@Test
 	void resolveUrlWebJarResource() {
-		String file = "underscorejs/underscore.js";
-		String expected = "underscorejs/1.8.3/underscore.js";
+		String file = "momentjs/momentjs.js";
+		String expected = "momentjs/2.29.4/momentjs.js";
 		given(this.chain.resolveUrlPath(file, this.locations)).willReturn(Mono.empty());
 		given(this.chain.resolveUrlPath(expected, this.locations)).willReturn(Mono.just(expected));
 
@@ -92,10 +94,24 @@ class LiteWebJarsResourceResolverTests {
 		verify(this.chain, times(1)).resolveUrlPath(expected, this.locations);
 	}
 
+	@Test
+	void resolveUrlWebJarDirectory() {
+		String folder = "momentjs/locale/";
+		String expected = "momentjs/2.29.4/locale/";
+		given(this.chain.resolveUrlPath(folder, this.locations)).willReturn(Mono.empty());
+		given(this.chain.resolveUrlPath(expected, this.locations)).willReturn(Mono.empty());
+
+		String actual = this.resolver.resolveUrlPath(folder, this.locations, this.chain).block(TIMEOUT);
+
+		assertThat(actual).isEqualTo(expected);
+		verify(this.chain, times(1)).resolveUrlPath(folder, this.locations);
+		verify(this.chain, times(1)).resolveUrlPath(expected, this.locations);
+	}
+
 	@Test
 	void resolveUrlWebJarResourceNotFound() {
-		String file = "something/something.js";
-		given(this.chain.resolveUrlPath(file, this.locations)).willReturn(Mono.empty());
+		String file = "momentjs/locale/unknown.js";
+		given(this.chain.resolveUrlPath(anyString(), eq(this.locations))).willReturn(Mono.empty());
 
 		String actual = this.resolver.resolveUrlPath(file, this.locations, this.chain).block(TIMEOUT);
 
@@ -134,11 +150,11 @@ class LiteWebJarsResourceResolverTests {
 
 	@Test
 	void resolveResourceWebJar() {
-		String file = "underscorejs/underscore.js";
+		String file = "momentjs/momentjs.js";
 		given(this.chain.resolveResource(this.exchange, file, this.locations)).willReturn(Mono.empty());
 
 		Resource expected = mock();
-		String expectedPath = "underscorejs/1.8.3/underscore.js";
+		String expectedPath = "momentjs/2.29.4/momentjs.js";
 		given(this.chain.resolveResource(this.exchange, expectedPath, this.locations))
 				.willReturn(Mono.just(expected));
 
diff --git a/spring-webmvc/spring-webmvc.gradle b/spring-webmvc/spring-webmvc.gradle
index 760530e3c87..194278ad7c0 100644
--- a/spring-webmvc/spring-webmvc.gradle
+++ b/spring-webmvc/spring-webmvc.gradle
@@ -80,5 +80,5 @@ dependencies {
 	testRuntimeOnly("org.glassfish:jakarta.el")
 	testRuntimeOnly("org.jruby:jruby")
 	testRuntimeOnly("org.python:jython-standalone")
-	testRuntimeOnly("org.webjars:underscorejs")
+	testRuntimeOnly("org.webjars:momentjs:2.29.4")
 }
diff --git a/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolver.java b/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolver.java
index 1486063b0e2..358927ab1e7 100644
--- a/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolver.java
+++ b/spring-webmvc/src/main/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolver.java
@@ -88,7 +88,10 @@ public class LiteWebJarsResourceResolver extends AbstractResourceResolver {
 		if (path == null) {
 			String webJarResourcePath = findWebJarResourcePath(resourceUrlPath);
 			if (webJarResourcePath != null) {
-				return chain.resolveUrlPath(webJarResourcePath, locations);
+				path = chain.resolveUrlPath(webJarResourcePath, locations);
+				if (path == null && webJarResourcePath.endsWith("/")) {
+					path = webJarResourcePath;
+				}
 			}
 		}
 		return path;
diff --git a/spring-webmvc/src/test/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolverTests.java b/spring-webmvc/src/test/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolverTests.java
index 101c0630692..724ab79d87a 100644
--- a/spring-webmvc/src/test/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolverTests.java
+++ b/spring-webmvc/src/test/java/org/springframework/web/servlet/resource/LiteWebJarsResourceResolverTests.java
@@ -26,6 +26,8 @@ import org.springframework.core.io.Resource;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
@@ -74,8 +76,8 @@ class LiteWebJarsResourceResolverTests {
 
 	@Test
 	void resolveUrlWebJarResource() {
-		String file = "underscorejs/underscore.js";
-		String expected = "underscorejs/1.8.3/underscore.js";
+		String file = "momentjs/momentjs.js";
+		String expected = "momentjs/2.29.4/momentjs.js";
 		given(this.chain.resolveUrlPath(file, this.locations)).willReturn(null);
 		given(this.chain.resolveUrlPath(expected, this.locations)).willReturn(expected);
 
@@ -86,10 +88,24 @@ class LiteWebJarsResourceResolverTests {
 		verify(this.chain, times(1)).resolveUrlPath(expected, this.locations);
 	}
 
+	@Test
+	void resolveUrlWebJarDirectory() {
+		String folder = "momentjs/locale/";
+		String expected = "momentjs/2.29.4/locale/";
+		given(this.chain.resolveUrlPath(folder, this.locations)).willReturn(null);
+		given(this.chain.resolveUrlPath(expected, this.locations)).willReturn(null);
+
+		String actual = this.resolver.resolveUrlPath(folder, this.locations, this.chain);
+
+		assertThat(actual).isEqualTo(expected);
+		verify(this.chain, times(1)).resolveUrlPath(folder, this.locations);
+		verify(this.chain, times(1)).resolveUrlPath(expected, this.locations);
+	}
+
 	@Test
 	void resolveUrlWebJarResourceNotFound() {
-		String file = "something/something.js";
-		given(this.chain.resolveUrlPath(file, this.locations)).willReturn(null);
+		String file = "momentjs/locale/unknown.js";
+		given(this.chain.resolveUrlPath(anyString(), eq(this.locations))).willReturn(null);
 
 		String actual = this.resolver.resolveUrlPath(file, this.locations, this.chain);
 
@@ -125,8 +141,8 @@ class LiteWebJarsResourceResolverTests {
 	@Test
 	void resolveResourceWebJar() {
 		Resource expected = mock();
-		String file = "underscorejs/underscore.js";
-		String expectedPath = "underscorejs/1.8.3/underscore.js";
+		String file = "momentjs/momentjs.js";
+		String expectedPath = "momentjs/2.29.4/momentjs.js";
 		given(this.chain.resolveResource(this.request, expectedPath, this.locations)).willReturn(expected);
 
 		Resource actual = this.resolver.resolveResource(this.request, file, this.locations, this.chain);
diff --git a/spring-websocket/src/main/java/org/springframework/web/socket/adapter/AbstractWebSocketSession.java b/spring-websocket/src/main/java/org/springframework/web/socket/adapter/AbstractWebSocketSession.java
index 0b638543826..46f4fc10421 100644
--- a/spring-websocket/src/main/java/org/springframework/web/socket/adapter/AbstractWebSocketSession.java
+++ b/spring-websocket/src/main/java/org/springframework/web/socket/adapter/AbstractWebSocketSession.java
@@ -24,9 +24,9 @@ import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.jspecify.annotations.Nullable;
 
-import org.springframework.util.AlternativeJdkIdGenerator;
 import org.springframework.util.Assert;
 import org.springframework.util.IdGenerator;
+import org.springframework.util.JdkIdGenerator;
 import org.springframework.web.socket.BinaryMessage;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.PingMessage;
@@ -44,7 +44,7 @@ import org.springframework.web.socket.WebSocketSession;
  */
 public abstract class AbstractWebSocketSession<T> implements NativeWebSocketSession {
 
-	protected static final IdGenerator idGenerator = new AlternativeJdkIdGenerator();
+	protected static final IdGenerator idGenerator = new JdkIdGenerator();
 
 	protected static final Log logger = LogFactory.getLog(NativeWebSocketSession.class);