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* **`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**.\
* **`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:
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.
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](https://www.baronsoftware.com/Blog/sql-stored-procedures-get-folder-files/). This method has been used in [multiple examples](https://www.notsosecure.com/oob-exploitation-cheatsheet/) of [Out of Band Data exfiltration](https://gracefulsecurity.com/sql-injection-out-of-band-exploitation/) posts on the Internet.
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`**](https://social.technet.microsoft.com/wiki/contents/articles/40107.xp-fileexist-and-its-alternate.aspx) 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:
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](https://github.com/infiniteloopltd/SQLHttp) 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](https://ibreak.software/2020/06/using-sql-injection-to-perform-ssrf-xspa-attacks/) as specified
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;`)
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.
**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.
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