Merge branch '6.0.x' into 6.1.x

Closes gh-14117

Author: jzheaux

web/src/main/java/org/springframework/security/web/authentication/ui/DefaultLoginPageGeneratingFilter.java

@@ -35,6 +35,7 @@
 import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;
 import org.springframework.security.web.authentication.rememberme.AbstractRememberMeServices;
 import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
 import org.springframework.web.filter.GenericFilterBean;
 import org.springframework.web.util.HtmlUtils;
 
@@ -266,11 +267,17 @@ private String generateLoginPageHtml(HttpServletRequest request, boolean loginEr
 
 	private String getLoginErrorMessage(HttpServletRequest request) {
 		HttpSession session = request.getSession(false);
-		if (session != null && session
-			.getAttribute(WebAttributes.AUTHENTICATION_EXCEPTION) instanceof AuthenticationException exception) {
-			return exception.getMessage();
+		if (session == null) {
+			return "Invalid credentials";
 		}
-		return "Invalid credentials";
+		if (!(session
+			.getAttribute(WebAttributes.AUTHENTICATION_EXCEPTION) instanceof AuthenticationException exception)) {
+			return "Invalid credentials";
+		}
+		if (!StringUtils.hasText(exception.getMessage())) {
+			return "Invalid credentials";
+		}
+		return exception.getMessage();
 	}
 
 	private String renderHiddenInputs(HttpServletRequest request) {

web/src/test/java/org/springframework/security/web/authentication/DefaultLoginPageGeneratingFilterTests.java

@@ -171,4 +171,18 @@ public void generatesForSaml2LoginAndEscapesClientName() throws Exception {
 			.contains("<a href=\"/saml/sso/google\">Google &lt; &gt; &quot; &#39; &amp;</a>");
 	}
 
+	// gh-13768
+	@Test
+	public void generatesWhenExceptionWithEmptyMessageThenInvalidCredentials() throws Exception {
+		DefaultLoginPageGeneratingFilter filter = new DefaultLoginPageGeneratingFilter(
+				new UsernamePasswordAuthenticationFilter());
+		filter.setLoginPageUrl(DefaultLoginPageGeneratingFilter.DEFAULT_LOGIN_PAGE_URL);
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/login");
+		request.setQueryString("error");
+		request.getSession().setAttribute(WebAttributes.AUTHENTICATION_EXCEPTION, new BadCredentialsException(null));
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		filter.doFilter(request, response, this.chain);
+		assertThat(response.getContentAsString()).contains("Invalid credentials");
+	}
+
 }