Security issues of file upload in php_PHP tutorial

You can read /etc/passwd!

this paragraph. .

[File upload]
PHP automatically supports file upload based on RFC 1867. Let’s look at the following example:

< INPUT TYPE="SUBMIT">

The above code allows the user to select a file from the local machine. When submit is clicked, the file will be uploaded to the server. This is obviously a useful feature, but the way PHP responds makes it unsafe. When PHP first receives such a request, even before it starts parsing the called PHP code, it will first accept the file from the remote user and check whether the length of the file exceeds the value defined by the "$MAX_FILE_SIZE variable". If it passes these For testing, the file will be stored in a local temporary directory.

Therefore, an attacker can send arbitrary files to the host running PHP. Before the PHP program decides whether to accept the file upload, the file has already been stored on the server.

I will not discuss the possibility of using file upload to conduct a DOS attack on the server here.

Let's consider a PHP program that handles file uploads. As we said above, the file is received and stored on the server (the location is specified in the configuration file, usually /tmp), and the extension is usually Random, similar to "phpxXuoXG" form. The PHP program needs to upload the file's information in order to process it, and this can be done in two ways, one that was already used in PHP 3, and the other that was introduced after we made a security advisory on the previous method.

However, we can say with certainty that the problem still exists, and most PHP programs still use the old way to handle uploaded files. PHP sets four global variables to describe uploaded files, such as the above example:

$hello = Filename on local machine (e.g "/tmp/phpxXuoXG")
$hello_size = Size in bytes of file (e.g 1024)
$hello_name = The original name of the file on the remote system (e.g "c:\temp\hello.txt")
$hello_type = Mime type of uploaded file (e.g "text/ plain")

Then the PHP program starts processing the file specified according to "$hello". The problem is that "$hello" is not necessarily a variable set by PHP, and any remote user can specify it. If we use the following method:

http://vulnhost/vuln.php?hello=/etc/passwd&hello_size=10240&hello_type=text/plain&hello_name=hello.txt

results in the following PHP global variables (of course POST method is also possible (even Cookie)):

$hello = "/etc/passwd"
$hello_size = 10240
$hello_type = "text/plain"
$hello_name = "hello.txt"

The above form data just meets the variables expected by the PHP program, but at this time the PHP program no longer processes the uploaded file, but processes "/etc/passwd ” (often resulting in content exposure). This attack can be used to expose the contents of any sensitive file.

http://www.bkjia.com/PHPjc/314189.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/314189.htmlTechArticleYou can read /etc/passwd! this paragraph. . [File upload] PHP automatically supports file upload based on RFC 1867. Let's look at the following example: FORM METHOD="POST" ENCTYPE="multipart/form-data" INPUT...