漏洞分析 Spring Framework路径遍历漏洞（CVE-2024-38816）

漏洞概述

VMware Spring Framework是美国威睿（VMware）公司的一套开源的Java、JavaEE应用程序框架。该框架可帮助开发人员构建高质量的应用。

近期，监测到Spring Framework在特定条件下，存在目录遍历漏洞（网宿评分：高危、CVSS 3.1 评分：7.5）：

当同时满足使用 RouterFunctions 和 FileSystemResource 来处理和提供静态文件时，攻击者可构造恶意请求遍历读取系统上的文件。

目前该漏洞POC状态已在互联网公开，建议客户尽快做好自查及防护。

受影响版本

Spring Framework 5.3.0 - 5.3.39

Spring Framework 6.0.0 - 6.0.23

Spring Framework 6.1.0 - 6.1.12

其他更旧或者官方已不支持的版本

漏洞分析

根据漏洞描述（https://spring.io/security/cve-2024-38816）可知，关键变更在于如何处理静态资源路径。

https://github.com/spring-projects/spring-framework/commit/d86bf8b2056429edf5494456cffcb2b243331c49#diff-25869a3e3b3d4960cb59b02235d71d192fdc4e02ef81530dd6a660802d4f8707R4

这里改了两处，分别是：

webflux --> org.springframework.web.reactive.function.server.PathResourceLookupFunction

webmvc --> org.springframework.web.servlet.function.PathResourceLookupFunction

它们都旨在为 Web 应用程序提供静态内容的访问。

以webmvc --> org.springframework.web.servlet.function.PathResourceLookupFunction为例，展开分析。

先是动态处理了资源请求，确保只返回有效并且可访问的资源。

@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);}
}

接着对路径字符串进行规范化处理，确保返回的路径格式是有效的。

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 ? "/" : "");
}

最后从安全角度，确保路径不指向敏感目录，并且避免出现路径穿越的情况。

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("../");
}

简单阐明以后，不难发现上述代码做了敏感目录检查、url检查、路径穿越检查等操作，暂时没发现可疑点，所以我们需要进一步跟进

org.springframework.web.servlet.function.PathResourceLookupFunction#isInvalidPath()

查看一下它检查相对路径时，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;
}

这个方法主要对用户输入路径做了规范化处理，具体包括长度检查、不同操作系统下的路径分隔符处理等。看起来也做了严格的处理，但这一步存在问题。

String[] pathArray = delimitedListToStringArray(pathToUse, FOLDER_SEPARATOR);

具体来说，它是允许空元素存在的，假设路径字符串形如：

String pathToUse = “/static///…/…/Windows/win.ini”;

那么调用 delimitedListToStringArray 方法以后，pathArray即为

[“static”, “”, “”, “…”, “…”, “Windows”, “win.ini”]

而pathElements即为

再来看这一串：String pathToUse = “/static/…/…/Windows/win.ini”;

显然，pathArray中存在空元素会影响上级目录的处理，导致返回不同的结果，即存在安全隐患。

漏洞复现

实现目录穿越需要用到"…/"，结合上述分析，可通过这种方式实现。

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(“…/”);
}
}

但还需要结合上下文，继续构造payload。首先路径以斜杠开头时，StringUtils.cleanPath()方法会去掉路径的第个斜杠。

if (pathToUse.startsWith(FOLDER_SEPARATOR)) {prefix = prefix + FOLDER_SEPARATOR;pathToUse = pathToUse.substring(1);
}

那就需要多写一条"/“，构造”///…/"跳一级目录。

而在最初的org.springframework.web.servlet.function.PathResourceLookupFunction#apply()中，对路径做了规范化处理，即去掉连续的"/"

pathContainer = this.pattern.extractPathWithinPattern(pathContainer);
String path = processPath(pathContainer.value());

所以需要将多余的"/“变为”"，再借助StringUtils.cleanPath()方法重新转换回来。

normalizedPath = replace(normalizedPath, WINDOWS_FOLDER_SEPARATOR, FOLDER_SEPARATOR);

修复方案

目前官方已有可更新版本，建议受影响用户升级至最新版本：

https://github.com/spring-projects/spring-framework/tags

产品支持

网宿全站防护-WAF已支持对该漏洞利用攻击的防护，并持续挖掘分析其他变种攻击方式和各类组件漏洞，第一时间上线防护规则，缩短防护“空窗期”。