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What happens when you upload a malicious file?
Client-side attacks: Uploading malicious files can make the website vulnerable to client-side attacks such as XSS or Cross-site Content Hijacking. Uploaded files can be abused to exploit other vulnerable sections of an application when a file on the same or a trusted server is needed (can again lead to client-side or server-side attacks)
How is a vulnerability in a file upload field exploited?
Now there are two ways in which the vulnerable upload field accepts a file. 1. It can accept a file directly into the website. In that case, hackers can upload malicious files directly. This is called local file upload vulnerability. 2. Some upload fields don’t allow direct uploads.
How to prevent file upload vulnerabilities in PHP?
Mistake 2: There is no sanitization on the file name or contents. This allows an attacker to upload a file with a .php extension which can then be accessed by the attacker from the web and executed. Developers can avoid this mistake by sanitizing the file name so that it does not contain an extension that can execute code via the web server.
What happens if you upload a harmful extension?
Blacklisting file extensions keeps track of potentially harmful extensions. When a user uploads a file, the system checks the file extension to make sure it is not on the blacklist. If it is, the file is rejected. Unfortunately, this method may not be able to list all harmful extensions.
What happens when you upload files to a non-system drive?
Attackers may attempt to: Execute denial of service attacks. Upload viruses or malware. Compromise networks and servers in other ways. Security steps that reduce the likelihood of a successful attack are: Upload files to a dedicated file upload area, preferably to a non-system drive.
Can a server be compromised by a file upload?
Server-side attacks: The web server can be compromised by uploading and executing a web-shell which can run commands, browse system files, browse local resources, attack other servers, or exploit the local vulnerabilities, and so forth.
What are the consequences of unrestricted file upload?
Using a file upload helps the attacker accomplish the first step. The consequences of unrestricted file upload can vary, including complete system takeover, an overloaded file system or database, forwarding attacks to back-end systems, client-side attacks, or simple defacement.