Check_MK Werk 0984: Fix code injection for logged in users via automation url

ID: 0984 Title: Fix code injection for logged in users via automation url Component: WATO Level: 2 Class: Incompatible Change Version: 1.2.5i4 This fixes CVSS 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C. The description: <i>The check_mk applications uses insecure API calls, which allow an attacker to execute arbitrary code on the server by issuing just a single URL. The reason for this is the usage of the insecure "pickle" API call. Apparently this was modified as a security means from a former version, which used "eval"-like structures with untrusted input data. Anyhow, as the python API documentation clearly state, "pickle" should be considered unsafe as well, see: <tt>https://docs.python.org/2/library/pickle.html</tt>.</i> The fix replaces <tt>pickle<tt> with a module called <tt>ast</tt>. Unfortunately this module is not available on Centos/RedHat 5.X and Debian 5. On these systems WATO still uses <tt>pickle</tt>, even with this fix. <b>Note:</b> This change makes the current Check_MK versions incompatible to older versions. In a mixed environment with old and new Check_MK versions or with old and newer Python versions you have to force WATO to use the old unsafe method by setting <tt>wato_legacy_eval = True<tt> in <tt>multisite.mk</tt>. This can also be done with the new global WATO setting <i>Use unsafe legacy encoding for distributed WATO</i>.