For example, instead of injecting: `or 1=1- you can inject: ‘ or ‘a’=’a If the comment symbol is blocked, you can often craft your injected data such that it does not break the syntax of the surrounding query, even without using this.For example, the following two queries for Oracle and MS-SQL, respectively, are the equivalent of select ename, sal from emp where ename=’marcus’ : SELECT ename, sal FROM emp where ename=CHR(109)||CHR(97)|| CHR(114)||CHR(99)||CHR(117)||CHR(115) SELECT ename, sal FROM emp WHERE ename=CHAR(109)+CHAR(97) +CHAR(114)+CHAR(99)+CHAR(117)+CHAR(115) You can use various string functions to dynamically construct a string using the ASCII codes for individual characters. If you need to introduce a string into your attack payload, you can do this without needing quotes. The single quotation mark is not required if you are injecting into a numeric data field or column name.Filters of this kind are often vulnerable to bypasses, so you should try numerous tricks in this situation. For example, the application may remove or sanitize certain characters or may block common SQL keywords. In some situations, an application that is vulnerable to SQL injection may implement various input filters that prevent you from exploiting the flaw without restrictions. CRASH COURSE FOR FINDING SQL INJECTION IN WEBAPPS:PART 3
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