Catch base64 decode exception

Closes gh-15905

Author: kse-music

web/src/main/java/org/springframework/security/web/savedrequest/CookieRequestCache.java

@@ -73,7 +73,13 @@ public SavedRequest getRequest(HttpServletRequest request, HttpServletResponse r
 		if (savedRequestCookie == null) {
 			return null;
 		}
-		String originalURI = decodeCookie(savedRequestCookie.getValue());
+		String originalURI;
+		try {
+			originalURI = decodeCookie(savedRequestCookie.getValue());
+		}
+		catch (IllegalArgumentException ex) {
+			return null;
+		}
 		UriComponents uriComponents = UriComponentsBuilder.fromUriString(originalURI).build();
 		DefaultSavedRequest.Builder builder = new DefaultSavedRequest.Builder();
 		int port = getPort(uriComponents);

web/src/test/java/org/springframework/security/web/savedrequest/CookieRequestCacheTests.java

@@ -213,4 +213,15 @@ private static String decodeCookie(String encodedCookieValue) {
 		return new String(Base64.getDecoder().decode(encodedCookieValue.getBytes()));
 	}
 
+	// gh-15905
+	@Test
+	public void illegalCookieValueReturnNull() {
+		CookieRequestCache cookieRequestCache = new CookieRequestCache();
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		request.setCookies(new Cookie(DEFAULT_COOKIE_NAME, "123^456"));
+		SavedRequest savedRequest = cookieRequestCache.getRequest(request, new MockHttpServletResponse());
+		assertThat(savedRequest).isNull();
+	}
+
+
 }