In light of last week’s CPU announcements, I invited my colleague Aviv Pode, Sentrigo’s Head of Security Research, to submit a special guest blog post. Thanks Aviv!
Oracle releases Critical Patch Updates (CPUs) every three months, containing security code fixes to vulnerabilities discovered by its security personnel or external researchers and hackers. By exploring these CPUs we can obtain valuable information about the vulnerabilities addressed by the patches and use them to create exploits that attack or hack the database. Thus, ironically, each time Oracle releases a new CPU to help protect databases, it actually increases the risk of Oracle databases worldwide being attacked.
This blog post describes and demonstrates the simple process of exploring Oracle’s CPUs to create working exploits that can be used to attack or hack an Oracle database. Only basic familiarity in information security and databases is required.
I will demonstrate the ease in which hackers can turn Oracle CPUs to attack vectors and its intent is to show IT security personnel the way their opponents operate. I’d like to emphasize that the best way to protect the databases against the hackers is a mix of several defense layers:
- You must apply the CPUs as soon as you can after they are released.
- You must harden the database and disable any functions in the database that you do not need.
- You should deploy security measures such as monitoring and virtual patching in order to augment the security.
Oracle Databases & Critical Patch Updates
Oracle is considered the leading and most widely used Database Management System (DBMS) in the enterprise world. Oracle databases are at the backbone of most critical or sensitive information systems in the world, from government and military, through telecommunications, commercial and financial companies, to some small businesses and web applications. Thus, Oracle databases store probably the most sensitive and valuable information in the world, anything from credit card information and personal health records to business transactions and national security documents.
In the past, Oracle installations contained weak default configurations, which made it easy for malicious users to penetrate Oracle databases. Among these weak default settings were active privileged user accounts with default known passwords, weak authentication settings and more. Since then, Oracle hardened these default settings, reducing many of the quick and easy attack methods that were publicly known and possible, leaving an interesting attack vector – built-in code vulnerability exploitation.
Code patches are released by software vendors to correct bugs discovered in their products. In many cases, these bugs affect security and the patches are actually fixes to security vulnerabilities that reside in the code itself. Oracle releases its Critical Patch Updates (CPUs) every three months since January 2005. These CPUs, which in the past contained fixes to bugs not only affecting security, now focus only on security related issues. Oracle, naturally, publishes very little information about the vulnerabilities or attack possibilities and refrain from delivering valuable information into the wrong hands. At most, Oracle indicates the high-level component being addressed or details the required privileges and severity level of the bug (using Common Vulnerability Scoring System [CVSS]).
However, the CPUs are not helping protect Oracle customers much. An interesting situation exists in most Oracle installations worldwide, severely compromising data confidentiality, integrity and availability in those systems. A survey conducted by Sentrigo showed that about 90 percent of Oracle customers do not install Oracle CPUs in the 6 months following their release, while about 60 percent do not install them at all – ever. This means that most of Oracle databases worldwide currently contain un-patched vulnerabilities in built-in components, which may be exploited by hackers or malicious users.
Exploring Oracle CPUs
Oracle CPUs are available for every supported chipset and operating system, as a compressed directory containing a bulk of sub-directories. The CPU contains meta-data for the entire patch, listing identification and very basic information about the bug fixes, stored in text and xml files. Each sub-directory is referred to as a ‘molecule’. Each molecule has a unique identification number. The molecule with the number corresponding to the name of the compressed directory is a special molecule with information about the entire CPU. Besides this special molecule, each molecule contains a fix of a different vulnerability found in a built-in component of Oracle. Inside each molecule we will find two sub-directories – “files” and “etc”. Under “files” we can find the corrected files, while under “etc” meta-data such as the location of the corrected files in the Oracle Home, the feature or component these files relate to or the affected versions of Oracle.
Oracle database CPUs usually contain fixes to four types of files: Binary, Java, PL/SQL and SQL files, although on occasion corrections are done in configuration and other types of files. The meta-data in the ‘etc’ sub-directory indicates how the ‘opatch’ (Oracle’s utility for applying patches) should apply this fix. Usually it indicates a simple ‘copy’ to replace a PL/SQL component or SQL script, or an ‘archive’ to store a fixed object (.o binary) file in an archive (.a) file. This can be viewed in the “actions” file, under “etc/config”.
Now that we know what kinds of files we expect to find inside the CPU, we can proceed to see how these files can be used to find and understand the vulnerabilities fixed by the patch.
Finding an exploitable vulnerability
In order to demonstrate, we will explore the July ‘08 CPU for Oracle 10.2.0.3 running on Linux 32 bit. After downloading and extracting the compressed file we will find 55 molecules. For our learning purpose we can pick a simple one, let’s say – 7154835. This molecule contains, under ‘files’, a single PLB file, to be stored in the directory specified in the ‘etc/config/actions’ file, under the Oracle Home.
PLB files are wrapped PL/SQL files, which contain the code of built-in Oracle components originally written in PL/SQL by Oracle. The PL/SQL code is wrapped using Oracle’s propriety wrapping algorithm. However, the algorithm for Oracle 9i wrapped code has been cracked and published by David Litchfield of NGS-Security at Black-Hat. Oracle 10g and 11g wrapping algorithm has not yet been published, however it is safe to assume that it is available to hackers worldwide. It is important to note here that even Oracle does not consider this wrapping algorithm to be anything more than an obfuscation and it is not cryptologically strong like PKI infrastructure, for example.
Once the PLB file has been unwrapped (using tools available for the hackers) we can view the plain text PL/SQL code. This can not only help us find the vulnerabilities that were patched, but actually find new unknown ones by analyzing the code – but this is a matter for another post 🙂 To continue with our demonstration, the PLB file we found in the molecule and unwrapped was ‘prvtdefr.plb’. We will locate and un-wrap the same file from an unpatched Oracle installation, or better-yet – patched with the previous CPU – April ’08. The file could be found in the same corresponding directory under the Oracle Home, as specified in the molecule meta-data ‘actions’ file – ‘$ORACLE_HOME/rdbms/admin/’.
Now we have two versions of the same Oracle built-in code file, one before and one after the code fix. All we need to do is compare the two files, locate the changes and in most cases a minimal additional effort will be required to understand the vulnerability.
Using a simple text-diff utility, we find several changed lines of code, which we can view in clear text. We can see that changes were made in the ‘dbms_defer_sys’ package, whose code is implemented here. Scrolling down we can examine the changes made in the ‘delete_tran_inner’ procedure. First, let’s look at the procedure header:
PROCEDURE DELETE_TRAN_INNER(DEFERRED_TRAN_ID IN VARCHAR2,
DESTINATION IN VARCHAR2, CATCHUP IN RAW) IS
We can see three parameters passed to this procedure, among them ‘DESTINATION’, a varchar2.
In the old PL/SQL file, before the code fix, inside the procedure we can see concatenation of parameters passed to the procedure, into new variables:
COND1 := 'd.deferred_tran_id=''' || DELETE_TRAN_INNER.DEFERRED_TRAN_ID
|| ''' AND ';
COND2 := 'd.dblink=''' || NLS_UPPER(DELETE_TRAN_INNER.DESTINATION)
|| ''' AND ';
These variables are later concatenated into an SQL SELECT statement and then executed:
DBMS_SQL.PARSE(SQLCURSOR, 'SELECT d.deferred_tran_id, d.dblink ' ||
'FROM "_DEFTRANDEST" d ' ||
'WHERE ' || COND1 || COND2 || COND3 || ' 1 = 1', DBMS_SQL.V7);
IGNORE := DBMS_SQL.EXECUTE(SQLCURSOR);
Let us now examine the corresponding lines in the new fixed code:
COND1 := 'd.deferred_tran_id=:deferred_tran_id AND ';
COND2 := 'd.dblink=:destination AND ';
We can see that bind variables are used, as a safe way to avoid SQL Injection vulnerabilities. From these code changes we can conclude that the patch is intended to fix an SQL injection vulnerability in the old PL/SQL code. However, the ‘delete_tran_inner’ is a private procedure, which a user cannot execute directly. In this simple case, a closer look will find a public ‘delete_tran’ procedure that a user can execute directly, which in turn calls the ‘delete_tran_inner’ without performing input validation or sanitization either. We can now continue to create an exploit for this vulnerability.
Creating an Exploit
After locating the fixed vulnerability and identifying the weak procedure and parameters which we can exploit, we can write (or copy from the web) an exploit and simply adjust it to target our vulnerable procedure. The code we found opens a cursor which grants DBA privileges to Scott, the malicious user account we will use to hack the database. By calling the ‘delete_tran’ procedure in ‘dbms_defer_sys’ and passing an SQL injection, we can execute the evil cursor:
C := DBMS_SQL.OPEN_CURSOR;
EXECUTE IMMEDIATE ''grant DBA to SCOTT'';
DBMS_DEFER_SYS.DELETE_TRAN('x',''' and 1=DBMS_SQL.EXECUTE('||C||')--');
Theoretically, executing this code on an Oracle 10.2.03 un-patched with the July ’08 CPU will result in Scott being granted DBA privileges to the entire database. As a side note, this code will not work on an 11g database because the dbms_sql package was hardened to check if privileges have changed between the parse and the execute stages.
This demonstration focused on a PL/SQL molecule. Many molecules contain binary files which we cannot examine as easily as what we have seen here. In order to examine these binary files, more sophisticated tools (than ‘diff’) are required, such as DataResue’s IDA-Pro and Zynamics BinDiff. However, the idea remains the same – compare the old and new code, find the changed function, understand the fix and create a targeted exploit. In such more complex cases, if you have found the code fix but do not understand the vulnerability or do not know how to successfully exploit it, a fuzzer may come in handy. Running a good fuzzer on the old version of the fixed function or procedure will, in many cases, reveal the information hackers are looking for.
As we have demonstrated, using Oracle’s CPUs to find vulnerabilities and create working exploits that target, attack and hack Oracle databases is quite simple. As a result, hackers and malicious users can easily create such exploits and publish them on the web for other users to utilize. In actuality, this means every time Oracle releases a CPU, hackers are given more critical information on how to successfully attack Oracle databases, which increases the risk level for Oracle installations worldwide.
The conclusion is simple: Apply patches AS SOON AS POSSIBLE. Harden your database by disabling unnecessary components. Or in case your organization is part of the majority of users who cannot afford it, for availability (downtime) practical or sensitivity considerations – apply a security measure such as virtual patching to block attacks targeting the database.