Web應用防護系統（也稱：網站應用級入侵防禦系統。英文：Web Application Firewall，簡稱： WAF）。利用國際上公認的一種說法：Web應用防火牆是通過執行一系列針對HTTP/HTTPS的安全策略來專門爲Web應用提供保護的一款產品。本文 介紹了常見的WAF指紋識別的一些技術，詳見如下：
WAF指紋
Cookie值
Citrix Netscaler
“Citrix Netscaler”會在HTTP返回頭部Cookie位置加入“ns_af”的值，可以以此判斷爲Citrix Netscaler的WAF，國內此類WAF很少（這貨居然是searchsecurity認定的2013最好的防火牆）。
一個惡意的請求示例：
GET / HTTP/1.1
Host: target.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: ASPSESSIONIDAQQSDCSC=HGJHINLDNMNFHABGPPBNGFKC; ns_af=31+LrS3EeEOBbxBV7AWDFIEhrn8A000;ns_af_.target.br_%2F_wat=QVNQU0VTU0lPTklEQVFRU0RDU0Nf?6IgJizHRbTRNuNoOpbBOiKRET2gA&
Connection: keep-alive
Cache-Control: max-age=0
F5 BIG IP ASM
F5 BiG IP ASM會在Cookie中加入“TS+隨機字符串”的Cookie信息，一個非惡意的請求如下：
GET / HTTP/1.1
Host: www.target.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Cookie: target_cem_tl=40FC2190D3B2D4E60AB22C0F9EF155D5; s_fid=77F8544DA30373AC-31AE8C79E13D7394; s_vnum=1388516400627%26vn%3D1; s_nr=1385938565978-New; s_nr2=1385938565979-New; s_lv=1385938565980; s_vi=[CS]v1|294DCEC0051D2761-40000143E003E9DC[CE]; fe_typo_user=7a64cc46ca253f9889675f9b9b79eb66; TSe3b54b=36f2896d9de8a61cf27aea24f35f8ee1abd1a43de557a25c529fe828; TS65374d=041365b3e678cba0e338668580430c26abd1a43de557a25c529fe8285a5ab5a8e5d0f299
Connection: keep-alive
Cache-Control: max-age=0
HTTP響應
Mod_Security
Mod_Security是爲Apache設計的開源Web防護模塊，一個惡意的請求Mod_Security會在響應頭返回“406 Not acceptable”的信息。
請求：
GET /<script>alert(1);</script>HTTP/1.1
Host: www.target.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
響應：
HTTP/1.1 406 Not Acceptable
Date: Thu, 05 Dec 2013 03:33:03 GMT
Server: Apache
Content-Length: 226
Keep-Alive: timeout=10, max=30
Connection: Keep-Alive
Content-Type: text/html; charset=iso-8859-1
<head><title>Not Acceptable!</title></head><body><h1>Not Acceptable!</h1><p>An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security.</p></body></html>
WebKnight
WebKnight是用來設計在IIS下面使用的WAF設備，較爲常見。WebKnight會對惡意的請求返回“999 No Hacking”的信息。
請求：
GET /?PageID=99<script>alert(1);</script>HTTP/1.1
Host: www.aqtronix.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
響應：
HTTP/1.1 999 No Hacking
Server: WWW Server/1.1
Date: Thu, 05 Dec 2013 03:14:23 GMT
Content-Type: text/html; charset=windows-1252
Content-Length: 1160
Pragma: no-cache
Cache-control: no-cache
Expires: Thu, 05 Dec 2013 03:14:23 GMT
F5 BIG IP
F5 BIG IP會對惡意請求返回“419 Unknown”的信息，如下：
GET /<script> HTTP/1.0
HTTP/1.1 419 Unknown
Cache-Control: no-cache
Content-Type: text/html; charset=iso-8859-15
Pragma: no-cache
Content-Length: 8140
Date: Mon, 25 Nov 2013 15:22:44 GMT
Connection: keep-alive
Vary: Accept-Encoding
dotDefender
dotDefender用來防護.net的程序，也比較出名，會對惡意請求返回“dotDefender Blocked Your Request”的信息。
請求：
GET /---HTTP/1.1
Host: www.acc.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Cache-Control: max-age=0
響應：
HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Type: text/html
Vary: Accept-Encoding
Server: Microsoft-IIS/7.5
X-Powered-By: ASP.NET
Date: Thu, 05 Dec 2013 03:40:14 GMT
Content-Length: 2616
<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>dotDefender Blocked Your Request</title>
……
特定資源文件
部分特定WAF在返回的告警頁面含特定的CSS或者JS文件，可以作爲判斷的依據，這類情況在WAF類裏比較少，實際也可以歸併到HTTP響應中。
看2個樣例：
<html><center><iframe width="100%" align="center" height="870" frameborder="0" scrolling="no" src="http://safe.webscan.360.cn/stopattack.html"></iframe></center> </body> </html>
HTTP/1.1 405 Not Allowed
Server: ASERVER/1.2.9-3
Date: Fri, 27 Dec 2013 14:15:14 GMT
Content-Type: text/html
Connection: keep-alive
X-Powered-By-Anquanbao: MISS from uni-tj-ky-sb3
Content-Length: 7188
<div class="wrapper">
<div class="titlelogo"></div>
<div class="err_tips">由於您訪問的URL有可能對網站造成安全威脅，您的訪問被阻斷。</div>
<div class="feedback">
<form action="http://report.anquanbao.com/api.php" method="post">
<input type="hidden" name="black_code" value="" class="hidden_rule_id" />
<input type="hidden" name="deny_time" value="" class="hidden_intercept_time" />
<input type="hidden" name="server_id" value="" class="hidden_server_title" />
<input type="hidden" name="deny_url" value="" class="deny_url" />
<input type="submit" class="submit_img" value="" />
</form>
</div>
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規則ID:10384
攔截時間：2013/12/27 22:15:14
ServerName：uni-tj-ky-sb3/1.2.9-3
WAF識別工具
一些WAF可以自定義返回的消息內容，或者全部返回自定義的404頁面或200頁面，有一些工具會協助作爲WAF設備的識別。
Wafw00f
用python編寫的一個小工具，開源地址：
http://code.google.com/p/waffit/source/browse/trunk/wafw00f.py
Wafw00f用來判斷WAF設備的函數如下：
AdminFolder = '/Admin_Files/'
xssstring = '<script>alert(1)</script>'
dirtravstring = '../../../../etc/passwd'
cleanhtmlstring = '<invalid>hello'
isaservermatch = 'Forbidden ( The server denied the specified Uniform Resource Locator (URL). Contact the server administrator. )'
使用“python wafw00f.py -h”可以查看工具的使用方法，運行示例：
python wafw00f.py http://www.baidu.com/
基於Cookie的檢測
Wafw00f的探測大部分是基於Cookie的檢測。
F5asm 的檢測規則如下：
def isf5asm(self):
# credit goes to W3AF
return self.matchcookie('^TS[a-zA-Z0-9]{3,6}=')
基於響應頭的檢測
Profense在響應頭會包含’server’,’profense’的信息。
def isprofense(self):
"""
Checks for server headers containing "profense"
"""
return self.matchheader(('server','profense'))
sqlmap
Sqlmap是一款檢測和利用SQLi漏洞工具，也是基於python編寫，業內認同率較高，sqlmap用來探測WAF類型想比較Wafw00f來說還多一些。
參考：
https://github.com/sqlmapproject/sqlmap/tree/master/waf
Sqlmap用來探測每種WAF設備都是一個python文件，同樣是從cookie信息或者返回頭信息進行判斷。
以Mod_Security爲例
#!/usr/bin/env python
"""
Copyright (c) 2006-2013 sqlmap developers (http://sqlmap.org/)
See the file 'doc/COPYING' for copying permission
"""
import re
from lib.core.enums import HTTP_HEADER
from lib.core.settings import WAF_ATTACK_VECTORS
__product__ = "ModSecurity: Open Source Web Application Firewall (Trustwave)"
def detect(get_page):
retval = False
for vector in WAF_ATTACK_VECTORS:
page, headers, code = get_page(get=vector)
retval = code == 501 and re.search(r"Reference #[0-9A-Fa-f.]+", page, re.I) is None
retval |= re.search(r"Mod_Security|NOYB", headers.get(HTTP_HEADER.SERVER, ""), re.I) is not None
if retval:
break
return retval
Sqlmap用來探測WAF的命令如下：
python sqlmap.py -u “http://www.baidu.com ex.php?id=1” --identify-waf
貌似必須是或自己修改的類似動態參數才能使用。
xenoitx
檢測和利用XSS漏洞的神器，WAF檢測也是其中的功能之一。