ERNW has a new baby, so please say “hello” to the new ERNW SecTools GmbH ;-).
But why another ERNW company? Short answer: Because we want to contribute to changing the way how software is built today: insecure, focused on profit and sometimes made by people who ignore lessons from history. So how can we contribute in this space? Start changing it ;-).
Our new workshop about TLS/SSL in the enterprise will be held for the 1st time at Troopers 2018. So I would like to take the opportunity and post a short teaser about stuff we will cover in this workshop.
Our new workshop about mobile application testing, held for the 1st time at the Troopers conference 2013, is coming closer. So I would like to take the opportunity and post an appetizer for those who are still undetermined if they should attend the workshop ;-).
While the topic of mobile application testing is a wide field that may contain reverse engineering, secure storage analysis, vulnerability research, network traffic analysis and so forth, in the end of the day you have to answer one question: Can I trust this application and run it on my enterprise devices? So first you have to define some criteria, which kind of behavior and characteristics of an application you regard as trustworthy (or not). Let us peek at malware … besides harming your devices and data, malware is typically:
obfuscated and/or encrypted
contains anti-debugging features
contains anti-reverse engineering features
This makes the analysis process a difficult task and comparing these characteristics especially to ordinary iOS applications from the AppStore, at least one is also true for these apps: Those are encrypted and are only decrypted at runtime on your Apple gadget ;-).
Actually a Windows Vulnerability (Microsoft Advisory 2757760) related to the Internet Explorer Version 7, 8 and 9 is in the news. Microsoft is aware of the problem, but there’s no patch available yet. We call this a 0-Day :-). Making the problem even worse, on monday reliable exploit code was released within the Metasploit project, so exploit code is already in the wild.
Disabling Active X and Active Scripting in the Internet Settings
But both of them have some impact: EMET must be deployed before any usage (btw. EMET can be configured via Group Policies) and disabling Active X and Active Scripting might break some business relevant web sites (that can be added to the “Trusted Sites” Zone, but might produce major operational effort).
There are more possible mitigating controls, so let’s just summarize some ideas:
Use of alternative browser: if you have it deployed already, go for it :-). Otherwise we have the same deployment issue as with EMET.
Sandboxing/Application Virtualization: It’s the same as with the alternate browser, of you have it, go for it, otherwise it will be a long term project. And be aware that also Application Virtualization won’t address all issues (see the ERNW Newsletter 32 for details).
No local admin rights: This doesn’t protect from exploiting the vulnerability, but at least reduces the impact. We strictly recommend to check the local administrator group and remove all users that don’t rely on it for fulfilling their business tasks. And btw. this topic is not new ;-), see also ERNW Newsletter 4, published in 2004!
Blocking communication for the clients at the corporate firewall: Be aware that this doesn’t really work. Modern exploit code is able to use the corporate proxy infrastructure including authentication to circumvent this control. Metasploit has exploit payloads for this.
Disabling/Blocking Flash content: While potentially not strictly required for exploitation, at least in some of the exploits currently observed in the wild Adobe Flash plays a major role. So like discussed in these Insinuator posts (1, 2 and 3), restricting the use of Adobe Flash would proactively prevent some known exploits from working. But the newly published Metasploit exploit doesn’t use Flash, so keep in mind that this mitigating control can only be used in addition to other ones.
So for a short term mitigation we recommend the following (especially for corporate environments)
Disabling Active X and Active Scripting via Group Policies
Disable/block Flash content
Remove unneeded local administrative privileges
If available use alternative browser or EMET
For long term mitigation (might also be feasible in small environments as short term mitigation):
Evaluate possibilities of application sandboxing/virtualization
Deploy alternative browser. Be aware that deploying a second browser might not be an option for big corporate environments (central management and supporting/maintaining additional software are the main reasons for this).
And finally DON’T PANIC ;-), start to address the problem in a professional way.
The product is commonly used in the swiss banking industry to ensure PCI DSS compliance and serves as another proof that WAFs can’t protect web applications from skilled attackers as already stated by me in an earlier post that you can find here. Beside these “5 myths of web application firewalls” we can also look at WAFs based on the typical attack vectors against web applications:
These attack vectors are described in detail in the famous “Web Application Hackers Handbook” and if you’re doing web application assessments they belong to the mandatory test methodology. Based on our WAF research we have compiled a little nice diagram that reflects the technical capabilities of WAFs to protect against these attack vectors:
As you can see especially authorization (user A can access data of user B) attacks and also logic flaws can not be addressed by WAFs because they can not be detected by pattern matching and even by whitelisting approaches. By the way when testing banking web applications one of the most relevant questions to answer is “can customer A see account information of customer B” :-). This raises the question “Why is the banking industry using WAFs to protect their customers data instead of fixing vulnerabilities in their applications or in general ensuring the quality?”. And again, finally we end up realizing that implementing a Security Development Lifecycle (SDL) would fulfill our “security needs” in a more effective way, but this time just from an attackers point of view.
If you want to extract some data from a database you first need to gather knowledge about the internal structure of the database.
One of the first steps (after determining the database type) is enumerating the available tables and the corresponding columns. Most database systems have a meta database called information_schema. By querying this database it is possible to get information about the internal structure of the installed databases. For example you could get the tables and their corresponding columns in MS SQL and MySQL by injecting “SELECT table_name, column_name FROM information_schema.columns“. Oracle databases have their own meta tables, so you have to handle them differently. For getting the same output in Oracle, you have to query the all_tab_columns table (or user_tab_columns if you only want to search in the currently selected database). If the found vulnerability only allows to receive a single column (or if it is too complicated to identify two columns in the server response) you could concatenate the columns to one single string, e.g. in Oracle: “SELECT table_name||':'||column_name FROM all_tab_columns“.
A much more frequent problem you have to deal with is that only the first row of a result-set is returned. To get all table and column names you have to iterate over the results. It is helpful to determine the expected row count first by injecting a “SELECT COUNT(column_name) FROM all_tab_columns“. Iterating over the results in MySQL is simple: “SELECT table_name, column_name FROM information_schema.columns LIMIT $start,1” (where $start denotes the current offset in the result-set). MS SQL doesn’t support to specify ranges for the results. This is why you have to combine several select statements to get the same result:
SELECT TOP 1 table_name, column_name FROM (SELECT TOP $start table_name, column_name FROM information_schema.columns ORDER BY table_name DESC) ORDER BY table_name ASC
(where $start denotes the row number you want to extract).
If you are confronted with a large database, it is always easier to search for interesting column names instead of tables. So you can combine the mentioned query statements with where clauses to search for columns which contain ‘pass’ or ‘user’.
If the found vulnerability is a blind or totally blind SQL injection, you have to use boolean expressions to extract some data. One approach is getting the database username (or any other data) by doing a binary search with the procedures ASCII and SUBSTR.
For example on Oracle databases you would get the first character of an username by injecting “ASCII(SUBSTR(username, 1,1))” into the where clause. To do a binary search on ‘Admin’ you would do “ASCII(SUBSTR(username, 1, 1)) < 128” which results in true. The next value to compare with is 64 (which is right in the middle of 0 and 128). This time the query would fail because the ascii value of ‘A’ is 65. Now you compare with 96 (the middle of 64 and 128) and so on, until you reach 65. After that you will treat the remaining characters in the same way.The following excerpt is an output from sqlninja (which will be covered again later on), which uses this technique in an automated way on a totally-blind SQLi vulnerability:
[ … ] ++++++++++++++++SQL Command++++++++++++++++
if ascii(substring((select system_user),1,1)) < 79 waitfor delay '0:0:5';
As the manual extraction of data can be quite time consuming, the usage of automated tools becomes essential. There are various tools that may help identifying and exploiting SQLi vulnerabilities. One of them is sqlmap, which concentrates on blind SQL injection, it comes with many options and supports a lot of different Database Servers (amongst them MS-SQL, MySQL, Oracle and PostgreSQL) which is one of the reasons why it is covered in this article. The extraction process is very intuitive and sqlmap tries to identify automatically the sort of SQLi (Blind, totally blind …) if not specified, so it is easy to get it up and running in a few minutes. We are not going into great detail, as this would go beyond the scope, but are showing a few commands which may already suffice to let sqlmap extract all available data from the database. Prerequisite for the following scenario is an already identified SQLi Vulnerability:
The first command tries to enumerate all available databases using the vulnerable parameter “txtUserName”:
The next command enumerates all available table names of the found databases without the need to specify the database names as all gathered information are stored in a local progress file and automatically used for all further attacks:(This feature becomes important as soon as the amount of already collected data gets vastly large.)
After using the same command but with the –columns option instead of –tables, enough necessary information were gathered to identify potential interesting tables of which now data can be extracted from. As this process might sometimes last too long, it is also possible to search for specific column names like “password” with the –search option. If however time doesn’t matter or the content is expected to be not very large, the –dump-all option may be used to extract all data contained in all databases.
As SQLi vulnerabilities enable an attacker not only to extract data, but sometimes also to execute system level commands, it is possible, and most tools offer such an option, to upload and execute binary files like e.g. netcat, resulting in an interactive shell with the same rights of the SQL server process (in the worst case root/administrative rights).Going one step further, sqlmap respectively sqlninja (a handy and in some cases less buggier than some others, but MS-SQL only SQLi tool) are able to use the exploitation framework Metasploit, which offers various attack payloads like “Creation of an administrative user” or a “Reverse-TCP shell”.In that way it is for example possible, to upload the powerful Meterpreter payload using an existing SQL injection vulnerability within a web application. Once started, Meterpreter enables system level access and can be used (depending on the rights of the database server process respectively the patch status of the underlying system) to extract system level data and utilize the database server as a jump host to an internal network or to exploit a local privilege escalation vulnerability to gain administrative rights.
An attacker uses an existing SQL injection vulnerability to upload and execute the meterpreter payload, then added a route entry within metasploit, making the internal network of the SQL server accessible through the meterpreter session and is now able to scan and attack systems behind the server, which would normally be not reachable from the attacker side.
Rating of the findings
After doing all the testing stuff, there’s one important step missing, at least if we are talking about a professional pentest. The criticality rating of findings is a mandatory task in the course of a pentest. On the one hand, the comparative value of the rating must be guaranteed, on the other hand, the rating must be appropriate for the environment which is in scope of the pentest. Based on these requirements, we propose the Common Weakness Scoring System as an appropriate metric for the rating of web application related security findings like SQL injection.The design considerations of CWSS include the applicability for scoring processes as well as the integration of stakeholder concerns or environmental requirements. These considerations result in the definition of three different metric groups which each contain different factors:
Different entities may evaluate separate factors at different points in time. As such, every CWSS factor effectively has “environmental” or “temporal” characteristics. Different pre-defined values can be assigned to each factor and each factor also has a default value. The different values for the single factors are explained in detail here:
CWSS uses also a reliability factor, so the factor Finding Confidence is explained as an example above.
All factors will be combined using a formula, which results in a value between 0 and 100. The higher a weakness is scored, the higher is the associated criticality. Regarding the formula and the used factors and weights, the CWSS allows a precise, comparable, and reproducible rating of vulnerabilities in the context of web application pentests. The rating will also help the application owner to prioritize the findings and use the always limited resources for the most critical issues.
Bringing the mentioned steps of the methodology together, you can follow a small checklist to identify all SQL injection issues in an application and help the application owner to mitigate the most severe problems. But every shortening of the test steps will have a negative influence on your success rate and the acceptance of the results:
1. Identify all input vectors
2. Test all input vector with a set of test signatures
3. Identify the database
4. Exploit the SQL injection vulnerability to proof the existence and avoid any discussions
5. Rate the criticality of the findings based on a metric
There are some database specifics, every pentester should be aware of, when testing for and exploiting SQLi vulnerabilities. Besides the different string concatenation variants already covered above, there are some other specifics that have to be considered and might turn out useful in some circumstances. For example with Oracle Databases, every SELECT statement needs a following FROM statement even if the desired data is not stored within a database. So when trying to extract e.g. the DB username using a UNION SELECT statement, the DUAL table may be utilized, which should always be available. Another point, if dealing with MySQL, is the possibility to simplify the classic payload
' or 1=1 --
' or 1 --
One important difference regarding totally-blind SQLi are the different ways for an equivalent MS-SQL “waitfor delay” in other database management systems. For MySQL (before 5.0.42), the benchmark function may be used. E.g.:
For later versions:
Respectively, Oracle supports an HTTP request function, which is expected to generate a delay if pointed to a non existing URL: utl_http.request('http://192.168.66.77/'). Alternatively, the following function may be useful:
Using database specific test and exploit signatures will also help to identify the used database, which makes all further tests much easier.
Another important difference is the missing MS-SQL “xp_cmdshell” on other DBMSs. However, there were some talks in the past (e.g. at Black Hat Europe 2009 by Bernardo Damele A. G. the author of sqlmap) about the possibility to execute code with MySQL respectively PostgreSQL under certain circumstances (sqlmap supports upload and execution of Metasploit shellcode for MySQL and PostgreSQL). This table summarizes useful SQL functions.
How to Exploit SQL Injection
After identifying vulnerable parameters it is time for exploitation. There are some basic techniques for this task, which will be explained in the context of an Oracle DB. As for data extraction one of the most useful statements is UNION SELECT. However, the UNION SELECT approach doesn’t work in all situations. If,for example, injecting right after the select statement (e.g. “SELECT $INPUT_COLUMN_NAME FROM tablename;” ) and not after a WHERE clause, trying to extract data with UNION SELECT leads most likely to an SQL error if you are unaware of the exact query. In this simple but sometimes occurring scenario, one solution would be the use of subselects. The advantage of subselects are the fact, that in many cases it is not necessary to know anything about the surrounding query. So supplying
(SELECT user FROM DUAL)
the SQL query doesn’t get broken and ideally prints the desired information. However if the payload is injected into a string, the previously covered string concatenation gets useful. So with a similar query, the attack string could look like:
'|| (SELECT user FROM DUAL) ||'
The previous examples depend on any form of results from the application. In case the application doesn’t print any results of the SQL query, it may still be possible to gather database information if the application behavior can be influenced.Given a registration form, where the supplied username gets checked for existence in the database, the used SQL query might look like:
SELECT username FROM users WHERE username = '$NEW_USERNAME';
This kind of vulnerability is a boolean-based blind SQLi. It is not possible to print any SQL query results, but the application logic can be exploited. So the payload in this case might be:
'|| (SELECT CASE WHEN (SELECT 'abcd' FROM DUAL) = 'abcd' THEN 'new_username' else 'EXISTING_USERNAME' END FROM DUAL)||'
Or in pseudo code:
If abcd equals abcd
Obviously this payload does not provide any useful information by now, but it illustrates the possibility to make boolean checks on strings which will be helpful later on during/for extracting real data from the database.
How to get around Web Application Firewalls
In some situations, the application might filter specific attack strings or a Web Application Firewall (WAF) is deployed in front of the web servers/applications. In these cases, being creative is essential. For example, instead of injecting
' or 'a'='a
we already circumvented a WAF by supplying a slightly modified version of this payload:
' or 'a='='a=
If dealing with a MySQL database, using the previously mentioned attack string might also (and did already in practice) help to deceive some filters:
' or 1 --
It is also very likely, that one single quote doesn’t cause any reaction, as of false positive prevention. If it does, the following variation could also help to get through the WAF:
In general, using short test strings (and some brainpower) might help to not trigger any filtering rules.
If unsure whether a WAF is in place or not, it is advisable to first verify its existence with some fingerprinting tools. One of them is wafw00f which supports many different vendors. Another tool is tsakwaf, which supports less vendors but includes additional features for WAF circumvention like encoding capabilities for test signatures, that might be useful for SQL injection testing, when a WAF is in place.
… to be continued …
Have a great day and enjoy trying 🙂
Michael, Timo and Frank from the Appsec Team
SQL injection attacks have been well known for a long time and many people think that developers should have fixed these issues years ago, but doing web application pentests almost all the time, we have a slightly different view. Many SQL injection problems potentially remain undetecteddue to a lack of proper test methodology, so we would like to share our approach and experience and help others in identifying these issues.
In march 2012 Microsoft announced a critical vulnerability (Microsoft Security Bulletin MS12-020) related to RDP that affects all windows operating systems and allows remote code execution. A lot of security professionals are expecting almost the same impact as with MS08-067 (the conficker vulnerability) and that it will be only a matter of time, until we will spot reliable exploits in the wild. Only a few days later an exploit, working for all unpatched windows versions was released, so it seems that they were right ;-), but of course no one will run an exploit without investigating the code. So lets have a look into the exploit Code.
First we take a look into the Microsoft advisory to get some information about the vulnerability itself:
The vulnerability requires some “specifically crafted RDP packets” to be sent to the vulnerable system to trigger the problem. We should spot this trigger in the exploit:
OK, the trigger is there and we also see some shellcode, that will open a bindshell on TCP port 8888. The next step is to figure out, what the exploit is doing with this code:
The exploit code converts a lot of opcodes to the big endian format, that looks reasonable because the exploit claims to work on all affected windows versions. The last step is to verifiy, how all the stuff is sent to the vulnerable system:
We see that target IP address and the RDP port are assigned and collected from the command line, the RDP packet is generated and the “specifically crafted RDP packets” are sent to the target.Finally the shellcode is sent and we are ready to connect to a remote shell that listens on TCP port 8888. Game over ;-).
We have verified the exploit, so it’s time now to run it against some unpatched test system and see, if we can compromise all these unpatched boxes out there …
…JUST KIDDING, never ever do that and I’m not talking about the legal issues this time ;-). It is a quite common mistake by unexperienced testers to work in this way. The exploit code was gathered from an untrusted source, so it needs detailed investigations before you run it, not just a short walk-through. You have to ensure that you understand every line of code completely to avoid being targeted by yourself, even the shellcode and the trigger of the rdp example. So let’s digg a little bit deeper into this.
First we have to extract the shellcode and trigger (the opcodes) from the exploit for further analysis. I prefer a special editor for this task that has all needed functionality (and much more 😉 ) built-in. It’s a commercial tool called “010 Editor” that can be obtained here and is available as a windows and MAC OS X version.
Copy just the trigger opcodes into a dedicated text file, don’t forget to remove the double quotes. The text files should look almost like this:
Use the editors replace function to replace “\x” with “0x” for the trigger and shellcode text files. Take the shellcode as an example, how the opcodes should look now:
Mark all this hex data and copy it to the clipboard.
Choose “File-New-New Hex File” from the “010 Editors” menu to create an empty hex file.
Now choose “Edit-Paste From-Paste from Hex Text” to paste the data as hex data into the new hex file.
Save both files (trigger and shellcode) as trigger.sc and shellcode.sc
Now we would be ready to analyze the opcodes with some toolset, but I assume that all of you already spotted some very interesting stuff within the shellcode part ;-):
Yes, it looks like the shellcode doesn’t open a bindshell, it just erases parts of your hard drive on windows and your complete root partition on unix.
This is really GAME OVER, if you would have run the exploit without a detailed analysis on a productive system. This code is referenced with the following code:
But in case that the shellcode wouldn’t have been so easily readable, there are more options for an easy analysis. Based on the shellcode emulation library libemu there are some tools available to find out what the shellcode is doing without reverse engineering it. SCDBG is one that runs on all unix based systems and also on windows, you can grab it here.
Let us see how SCDBG works with a short example shellcode: scdbg -f UrlDownloadToFile.sc
Loaded 150 bytes from file UrlDownloadToFile.sc
Max Steps: 2000000
Using base offset: 0x401000
So the example shellcode downloads a malicious file and executes it, let’s have a look at our shellocde now: scdbg -f shellcode.sc
Loaded 10d bytes from file shellcode.sc
Max Steps: 2000000
Using base offset: 0x401000
401002opcode 69 not supported
SCDBG fails to analyze the shellcode (for obvious reasons as we already know), so you can take this result as a good hint, that some stuff is hidden in the code and that you better shouldn’t run it.
So finally, let’s summarize some lessons that every serious penetration tester should be aware of:
1. Never run any untrusted code (especially exploits) without a detailed analysis.
2. Ensure that you understand every line of code and this also includes the shellcode.
3. Before using untrusted code in a real pentest, verify it in a test environment (virtual machines are a good choice for that).
4. When using exploits on customer systems be aware that you’re running it on one of the assets of your customer! Don’t do that without your customers permission!
5. Your customer trusts your professional knowledge, so it’s your responsibility to avoid damaging any of your customers systems by mistake.