漏洞概述
VMware Spring Framework是美國威睿（VMware）公司的一套開源的Java、JavaEE應用程序框架。該框架可幫助開發人員構建高質量的應用。
近期，監測到Spring Framework在特定條件下，存在目錄遍歷漏洞（網宿評分：高危、CVSS 3.1 評分：7.5）：
當同時滿足使用 RouterFunctions 和 FileSystemResource 來處理和提供靜態文件時，攻擊者可構造惡意請求遍歷讀取系統上的文件。
目前該漏洞POC狀態已在互聯網公開，建議客戶盡快做好自查及防護。
受影響版本
Spring Framework 5.3.0 - 5.3.39
Spring Framework 6.0.0 - 6.0.23
Spring Framework 6.1.0 - 6.1.12
其他更舊或者官方已不支持的版本
漏洞分析
根據漏洞描述（https://spring.io/security/cve-2024-38816）可知，關鍵變更在于如何處理靜態資源路徑。
https://github.com/spring-projects/spring-framework/commit/d86bf8b2056429edf5494456cffcb2b243331c49#diff-25869a3e3b3d4960cb59b02235d71d192fdc4e02ef81530dd6a660802d4f8707R4
這里改了兩處，分別是：
webflux --> org.springframework.web.reactive.function.server.PathResourceLookupFunction
webmvc --> org.springframework.web.servlet.function.PathResourceLookupFunction
它們都旨在為 Web 應用程序提供靜態內容的訪問。
以webmvc --> org.springframework.web.servlet.function.PathResourceLookupFunction為例，展開分析。
先是動態處理了資源請求，確保只返回有效并且可訪問的資源。
@Override
public Optional<Resource> apply(ServerRequest request) {PathContainer pathContainer = request.requestPath().pathWithinApplication();if (!this.pattern.matches(pathContainer)) {return Optional.empty();}pathContainer = this.pattern.extractPathWithinPattern(pathContainer);String path = processPath(pathContainer.value());if (path.contains("%")) {path = StringUtils.uriDecode(path, StandardCharsets.UTF_8);}if (!StringUtils.hasLength(path) || isInvalidPath(path)) {return Optional.empty();}try {Resource resource = this.location.createRelative(path);if (resource.isReadable() && isResourceUnderLocation(resource)) {return Optional.of(resource);}else {return Optional.empty();}}catch (IOException ex) {throw new UncheckedIOException(ex);}
}
接著對路徑字符串進行規范化處理，確保返回的路徑格式是有效的。
private String processPath(String path) {boolean slash = false;for (int i = 0; i < path.length(); i++) {if (path.charAt(i) == '/') {slash = true;}else if (path.charAt(i) > ' ' && path.charAt(i) != 127) {if (i == 0 || (i == 1 && slash)) {return path;}path = slash ? "/" + path.substring(i) : path.substring(i);return path;}}return (slash ? "/" : "");
}
最后從安全角度，確保路徑不指向敏感目錄，并且避免出現路徑穿越的情況。
private boolean isInvalidPath(String path) {if (path.contains("WEB-INF") || path.contains("META-INF")) {return true;}if (path.contains(":/")) {String relativePath = (path.charAt(0) == '/' ? path.substring(1) : path);if (ResourceUtils.isUrl(relativePath) || relativePath.startsWith("url:")) {return true;}}return path.contains("..") && StringUtils.cleanPath(path).contains("../");
}
簡單闡明以后，不難發現上述代碼做了敏感目錄檢查、url檢查、路徑穿越檢查等操作，暫時沒發現可疑點，所以我們需要進一步跟進
org.springframework.web.servlet.function.PathResourceLookupFunction#isInvalidPath()
查看一下它檢查相對路徑時，StringUtils.cleanPath()做了哪些操作。
public static String cleanPath(String path) {if (!hasLength(path)) {return path;}String normalizedPath;// Optimize when there is no backslashif (path.indexOf('\') != -1) {normalizedPath = replace(path, DOUBLE_BACKSLASHES, FOLDER_SEPARATOR);normalizedPath = replace(normalizedPath, WINDOWS_FOLDER_SEPARATOR, FOLDER_SEPARATOR);}else {normalizedPath = path;}String pathToUse = normalizedPath;// Shortcut if there is no work to doif (pathToUse.indexOf('.') == -1) {return pathToUse;}// Strip prefix from path to analyze, to not treat it as part of the// first path element. This is necessary to correctly parse paths like// "file:core/../core/io/Resource.class", where the ".." should just// strip the first "core" directory while keeping the "file:" prefix.int prefixIndex = pathToUse.indexOf(':');String prefix = "";if (prefixIndex != -1) {prefix = pathToUse.substring(0, prefixIndex + 1);if (prefix.contains(FOLDER_SEPARATOR)) {prefix = "";}else {pathToUse = pathToUse.substring(prefixIndex + 1);}}if (pathToUse.startsWith(FOLDER_SEPARATOR)) {prefix = prefix + FOLDER_SEPARATOR;pathToUse = pathToUse.substring(1);}String[] pathArray = delimitedListToStringArray(pathToUse, FOLDER_SEPARATOR);// we never require more elements than pathArray and in the common case the same numberDeque<String> pathElements = new ArrayDeque<>(pathArray.length);int tops = 0;for (int i = pathArray.length - 1; i >= 0; i--) {String element = pathArray[i];if (CURRENT_PATH.equals(element)) {// Points to current directory - drop it.}else if (TOP_PATH.equals(element)) {// Registering top path found.tops++;}else {if (tops > 0) {// Merging path element with element corresponding to top path.tops--;}else {// Normal path element found.pathElements.addFirst(element);}}}// All path elements stayed the same - shortcutif (pathArray.length == pathElements.size()) {return normalizedPath;}// Remaining top paths need to be retained.for (int i = 0; i < tops; i++) {pathElements.addFirst(TOP_PATH);}// If nothing else left, at least explicitly point to current path.if (pathElements.size() == 1 && pathElements.getLast().isEmpty() && !prefix.endsWith(FOLDER_SEPARATOR)) {pathElements.addFirst(CURRENT_PATH);}final String joined = collectionToDelimitedString(pathElements, FOLDER_SEPARATOR);// avoid string concatenation with empty prefixreturn prefix.isEmpty() ? joined : prefix + joined;
}
這個方法主要對用戶輸入路徑做了規范化處理，具體包括長度檢查、不同操作系統下的路徑分隔符處理等。看起來也做了嚴格的處理，但這一步存在問題。
String[] pathArray = delimitedListToStringArray(pathToUse, FOLDER_SEPARATOR);
具體來說，它是允許空元素存在的，假設路徑字符串形如：
String pathToUse = “/static///…/…/Windows/win.ini”;
那么調用 delimitedListToStringArray 方法以后，pathArray即為
[“static”, “”, “”, “…”, “…”, “Windows”, “win.ini”]
而pathElements即為
再來看這一串：String pathToUse = “/static/…/…/Windows/win.ini”;
顯然，pathArray中存在空元素會影響上級目錄的處理，導致返回不同的結果，即存在安全隱患。
漏洞復現
實現目錄穿越需要用到"…/"，結合上述分析，可通過這種方式實現。
package org.example.demo;
import org.springframework.util.ResourceUtils;
import org.springframework.util.StringUtils;public class test {
public static void main(String[] args) {
String path = “/static///…/…/Windows/win.ini”;
System.out.println(isInvalidPath(path));
}private static boolean isInvalidPath(String path) {
if (path.contains(“WEB-INF”) || path.contains(“META-INF”)) {
return true;
}
if (path.contains(“😕”)) {
String relativePath = (path.charAt(0) == ‘/’ path.substring(1) : path);
if (ResourceUtils.isUrl(relativePath) || relativePath.startsWith(“url:”)) {
return true;
}
}
return path.contains(“…”) && StringUtils.cleanPath(path).contains(“…/”);
}
}
但還需要結合上下文，繼續構造payload。首先路徑以斜杠開頭時，StringUtils.cleanPath()方法會去掉路徑的第個斜杠。
if (pathToUse.startsWith(FOLDER_SEPARATOR)) {prefix = prefix + FOLDER_SEPARATOR;pathToUse = pathToUse.substring(1);
}
那就需要多寫一條"/“，構造”///…/"跳一級目錄。
而在最初的org.springframework.web.servlet.function.PathResourceLookupFunction#apply()中，對路徑做了規范化處理，即去掉連續的"/"
pathContainer = this.pattern.extractPathWithinPattern(pathContainer);
String path = processPath(pathContainer.value());
所以需要將多余的"/“變為”"，再借助StringUtils.cleanPath()方法重新轉換回來。
normalizedPath = replace(normalizedPath, WINDOWS_FOLDER_SEPARATOR, FOLDER_SEPARATOR);
修復方案
目前官方已有可更新版本，建議受影響用戶升級至最新版本：
https://github.com/spring-projects/spring-framework/tags
產品支持
網宿全站防護-WAF已支持對該漏洞利用攻擊的防護，并持續挖掘分析其他變種攻擊方式和各類組件漏洞，第一時間上線防護規則，縮短防護“空窗期”。
)
)
