> 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/path-traversal/bypass-with-null-byte-and-extension-validation.md).
# 通过空字节和扩展名验证绕过
通过空字节和扩展名验证绕过笔记，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。
### 文件路径遍历，利用空字节绕过文件扩展名校验
此实验展示了在显示产品图片时存在的路径遍历漏洞。/ 应用程序会检查提供的文件名是否以预期的扩展名正确结尾。
目标是读取以下文件的内容 **/etc/passwd** 文件。
#### **分析**
如果直接提供路径
```bash
../../../../etc/passwd
```
应用程序返回错误，因为它要求文件具有扩展名 **.jpg**.
在较旧版本的 PHP（早于 **5.3.4**）中，可以使用零 **字节（%00）** 来绕过此校验：/ PHP 引擎会在空字节处停止读取文件名，而应用程序仍然会看到一个有效的扩展名。
#### **有效载荷**
在扩展名前添加一个空字节：
```bash
%00.jpg
```
浏览器仍会将“.jpg”解释为图片扩展名，但 PHP 会在“ /etc/passwd”处停止，这使你能够读取敏感文件。
```bash
../../../../etc/passwd%00.jpg
```
---
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