Date: Tue, 21 Jun 2016 11:45:01 +0200 From: Sebastian Krahmer <krahmer@...e.com> To: oss-security@...ts.openwall.com Subject: SELinux troubles Hi As per list policy, this is the repost to oss-sec. CRD was set to today. PoC may be found as straight-shooter.c inside old troubleshooter git. Please also note the container-damaging beauty this time. Sebastian ----8<--------------- Hi Due to a review request, it was necessary to have a look at setroubleshoot again. setroubleshoot (still) contains various code injection vulns, leading to full (unconfined) root. PoC has been tested on CentOS 6.6, 6.8 and 7. PoC as well works inside Docker containers to achieve running in a setroubleshoot domain with uid 0 on "the host". (PoC most likely also works on RHEL 6.x and 7 if CentOS maps to it). This is not CVE-2015-1815 and PoC runs on systems that are patched against it. Here are the details: 1) This bug is mitigated since setroubleshoot that is found on RHEL 7.2, by running it as a dedicated user (untested). Shell injection issue in setroubleshoot/audit_data.py: def _set_tpath(self): [...] if path.startswith("/") == False and inodestr: import subprocess command = "locate -b '\%s'" % path try: output = subprocess.check_output(command, stderr=subprocess.STDOUT, shell=True) [...] taking 'path' off AVC denial messages and constructing a command thats passed to "sh -c". o.O Note that AVC denial messages appear outside of containers, so a setroubleshoot is usually run on the host, processing AVC messages from containers. This allows for an easy breakout. 2) I did not test this, but even though the run_fix() function in SetroubleshootFixit.py is protected by auth_admin polkit rules, it looks like theres good chance to pass XML documents via setroubleshoots RPC/DBUS API that contains evil local_id or analysis_id fields and trick real admins to "fix" AVC denials that inject code: [...] def run_fix(self, local_id, analysis_id): import commands command = "sealert -f %s -P %s" % ( local_id, analysis_id) return commands.getoutput(command) [...] This is not mitigated by the run-as-user, since SetroubleshootFixit.py still runs as root (and probably needs to). There are various other occurences of subprocess calls for "rpm" and others, which have already been mentioned in the CVE-2015-1815 report but probably still unfixed because of "missing PoC". The codebase is huge, and I wonder what kind of lax handling and user-surfacing code inside critical SELinux components this is, in particular where SELinux' aim is to harden the system. Sebastian -- ~ perl self.pl ~ $_='print"\$_=\47$_\47;eval"';eval ~ krahmer@...e.com - SuSE Security Team
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