Home Backend Development PHP Tutorial 探讨:web上存漏洞及原理分析、防范方法_php技巧

探讨:web上存漏洞及原理分析、防范方法_php技巧

May 17, 2016 am 08:57 AM
Precautionary methods

网站提供上存功能,是很多站点经常会有功能,商城,论坛还有常见一些网盘站点。常见互联网上面,我们也是经常听说,某某站点出现上存漏洞,某某开源项目有上存漏洞。 从互联网开始出现动态程序,上存漏洞像幽灵一样,频繁的出现在各种系统中。为什么,一个上存漏洞会这么频繁出现呢。而且,有些系统反复修补,多次还没有修补成功!其实主要问题,还是出现在上存原理上面。我们先看看,上存过程。
网站上存过程分析

复制代码 代码如下:

header("Content-type: text/html; charset=utf-8");
if($_FILES)
{
 echo '
';<br> var_dump($_FILES);<br> echo '
Copy after login
';
}
?>





以上是个简单测试例子,我们看看

我们来分析下:
name来自 上存时候选择文件名称
type 是文件类型, 这个类型那里来的呢?呵呵,这里非常关键的。 很多时候,很多同人会认为,这个是服务器自动判断生成的。 如果是这样想,觉得也有可能。 php 封装了上存,它自带类库好像可以的。  但是,反过来想想,你随便选择个什么格式文件,都会有格式类型。这样一想,我们推断这个值,可能也来自用户输入的。 我们来抓包看看我们类型。

type值 也来自,用户输入值了。
size来自程序计算上存文件大小,这个是自动计算的。 相比我们都清楚的。

你说这么多有啥样呢?
想必有朋友开始问了,我上面分析上存文件格式 ,跟开发出现漏洞有什么关联呢。 其实,我们想想,上面说的,一个文件名称name属性,以及文件类型type属性。 在我们上存文件,后端处理时候,会经常用到的。 作为开发者,在使用这2个变量,一定要继续执行“一切输入代码是有害的”原则。你在使用时候,要把它当作,跟其它get,post 获取变量一样处理。 要检测,过滤一切输入变量。
我们经常做功能是,限定用户输入必须是某种格式文件,然后保存为该格式。分析到这里,下面有很多需要继续分析地方,今天先提出大纲。接下来会分析这样常见3类上存漏洞。
1.使用用户文件名,生成文件,特殊字符过滤不严格,导致文件生成出现漏洞
2.移动文件目录时候,由于采用用户传入的文件名拼接,生成到错误目录
3.相信用户输入type 类型,直接将用户文件名保存为文件

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