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# UNION Attack Column Count Detection

UNION Attack Column Count Detection notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### SQL Injection UNION Attack, Determining the Number of Columns Returned by the Query

* **Background:** `category` filter vulnerable to SQL injection; The application response includes SQL results, so a `UNION` allows to inject an additional visible line.
* **Objective:** find the exact number of columns returned by the original query to build compatible `UNION SELECT`.
* **Quick method:**

1. **Test with `ORDER BY`** — increment the index until an error occurs (the error indicates that the index exceeds the number of columns):

   ````
    ```sql
    ' ORDER BY 1-- -
    ' ORDER BY 2-- -
    ' ORDER BY 3-- -
    ```
   ````

* When `ORDER BY N` causes an error, the number of columns is `< N`.

2. Confirm by injecting an UNION line containing NULL — build a SELECT UNION with the same number of columns; if the application shows the injected line (null values), the number is correct. Example (3 columns):

   ```sql
   ' UNION SELECT NULL, NULL, NULL-- -
   ```

* If the row appears, the original query returns 3 columns. Otherwise, adjust the number of `NULL` and retest.

**Variantes utiles :**

* Use constants to locate the displayed column (useful if only some columns are returned):

  ```sql
  ' UNION SELECT 'A', 'B', 'C'-- -
  ```

(Lets visually identify which columns of the response correspond to the injected columns.)

* If UNION fails due to types, replace some constants with CAST(NULL AS VARCHAR2) / NULL according to DBMS, or adapt types with CAST/TO/ CHAR.

Expected result: an additional row containing NULL (or constants) will display → number of columns determined.


---

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