Security issues of file upload in php_PHP tutorial
Jul 21, 2016 pm 04:10 PM
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:
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.

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

PHPhasthreecommentstyles://,#forsingle-lineand/.../formulti-line.Usecommentstoexplainwhycodeexists,notwhatitdoes.MarkTODO/FIXMEitemsanddisablecodetemporarilyduringdebugging.Avoidover-commentingsimplelogic.Writeconcise,grammaticallycorrectcommentsandu

The key steps to install PHP on Windows include: 1. Download the appropriate PHP version and decompress it. It is recommended to use ThreadSafe version with Apache or NonThreadSafe version with Nginx; 2. Configure the php.ini file and rename php.ini-development or php.ini-production to php.ini; 3. Add the PHP path to the system environment variable Path for command line use; 4. Test whether PHP is installed successfully, execute php-v through the command line and run the built-in server to test the parsing capabilities; 5. If you use Apache, you need to configure P in httpd.conf

PHPisaserver-sidescriptinglanguageusedforwebdevelopment,especiallyfordynamicwebsitesandCMSplatformslikeWordPress.Itrunsontheserver,processesdata,interactswithdatabases,andsendsHTMLtobrowsers.Commonusesincludeuserauthentication,e-commerceplatforms,for

TohandlefileoperationsinPHP,useappropriatefunctionsandmodes.1.Toreadafile,usefile_get_contents()forsmallfilesorfgets()inaloopforline-by-lineprocessing.2.Towritetoafile,usefile_put_contents()forsimplewritesorappendingwiththeFILE_APPENDflag,orfwrite()w

The basic syntax of PHP includes four key points: 1. The PHP tag must be ended, and the use of complete tags is recommended; 2. Echo and print are commonly used for output content, among which echo supports multiple parameters and is more efficient; 3. The annotation methods include //, # and //, to improve code readability; 4. Each statement must end with a semicolon, and spaces and line breaks do not affect execution but affect readability. Mastering these basic rules can help write clear and stable PHP code.

How to start writing your first PHP script? First, set up the local development environment, install XAMPP/MAMP/LAMP, and use a text editor to understand the server's running principle. Secondly, create a file called hello.php, enter the basic code and run the test. Third, learn to use PHP and HTML to achieve dynamic content output. Finally, pay attention to common errors such as missing semicolons, citation issues, and file extension errors, and enable error reports for debugging.

The steps to install PHP8 on Ubuntu are: 1. Update the software package list; 2. Install PHP8 and basic components; 3. Check the version to confirm that the installation is successful; 4. Install additional modules as needed. Windows users can download and decompress the ZIP package, then modify the configuration file, enable extensions, and add the path to environment variables. macOS users recommend using Homebrew to install, and perform steps such as adding tap, installing PHP8, setting the default version and verifying the version. Although the installation methods are different under different systems, the process is clear, so you can choose the right method according to the purpose.

The key to writing Python's ifelse statements is to understand the logical structure and details. 1. The infrastructure is to execute a piece of code if conditions are established, otherwise the else part is executed, else is optional; 2. Multi-condition judgment is implemented with elif, and it is executed sequentially and stopped once it is met; 3. Nested if is used for further subdivision judgment, it is recommended not to exceed two layers; 4. A ternary expression can be used to replace simple ifelse in a simple scenario. Only by paying attention to indentation, conditional order and logical integrity can we write clear and stable judgment codes.
