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#PHP FILE UPLOAD SECURITY PDF#
#PHP FILE UPLOAD SECURITY ZIP#

In conjunction with content-type validation, validating the file's signature can be checked and verified against the expected file that should be received. This can be done preferably in an allow list approach otherwise, this can be done in a block list approach. Other than defining the extension of the uploaded file, its MIME-type can be checked for a quick protection against simple file upload attacks. Although it should not be relied upon for security, it provides a quick check to prevent users from unintentionally uploading files with the incorrect type. The Content-Type for uploaded files is provided by the user, and as such cannot be trusted, as it is trivial to spoof. The Unrestricted File Upload vulnerability article describes how attackers may attempt Please be aware that blocking specific extensions is a weak protection method on its own. Identify potentially harmful file types and block extensions that you regard harmful to your service.

#PHP FILE UPLOAD SECURITY PDF#

cv upload, allow docx and pdf extensions.īased on the needs of the application, ensure the least harmful and the lowest risk file types to be used.image upload, allow one type that is agreed upon to fit the business requirement.List Allowed Extensions ¶Įnsure the usage of business-critical extensions only, without allowing any type of non-required extensions.

Refer to the Input Validation CS to properly parse and process the extension. Refrain from building your own logic unless you have enough knowledge on this topic.

Generic bad regex that isn't properly tested and well reviewed.

Double extensions, e.g.jpg.php, where it circumvents easily the regex \.jpg.

Extension Validation ¶Įnsure that the validation occurs after decoding the file name, and that a proper filter is set in place in order to avoid certain known bypasses, such as the following: Implementing multiple techniques is key and recommended, as no one technique is enough to secure the service. Implementing a defense in depth approach is key to make the upload process harder and more locked down to the needs and requirements for the service. There is no silver bullet in validating user content. personal data, copyrighted data, etc.) which will make you a host for such malicious files.

File content that could be deemed as illegal, offensive, or dangerous ( e.g.

Requests are small, yet responses are much larger

Initiate a DoS attack by requesting lots of files.If the file uploaded is publicly retrievable, additional threats can be addressed: Client-side active content (XSS, CSRF, etc.) that could endanger other users if the files are publicly retrievable.Overwrite an existing file on the system.

#PHP FILE UPLOAD SECURITY ZIP#

Send ZIP bombs, XML bombs (otherwise known as billion laughs attack), or simply huge files in a way to fill the server storage which hinders and damages the server's availability.

Exploit vulnerabilities in the file parser or processing module ( e.g.

The attacker delivers a file for malicious intent, such as: The following sections will hopefully showcase the risks accompanying the file upload functionality. In order to assess and know exactly what controls to implement, knowing what you're facing is essential to protect your assets.

Protect the file upload from CSRF attacks.

Ensure that any libraries used are securely configured and kept up to date.

Run the file through an antivirus or a sandbox if available to validate that it doesn't contain malicious data.

In the case of public access to the files, use a handler that gets mapped to filenames inside the application (someid -> file.ext).

If that's not possible, store them outside of the webroot

Store the files on a different server.

Only allow authorized users to upload files.

Restrict the allowed characters if possible

Change the filename to something generated by the application.

Validate the file type, don't trust the Content-Type header as it can be spoofed.

Ensure that input validation is applied before validating the extensions.Only allow safe and critical extensions for business functionality In short, the following principles should be followed to reach a secure file upload implementation: The application should be able to fend off bogus and malicious files in a way to keep the application and the users safe. Insecure Direct Object Reference Preventionįile upload is becoming a more and more essential part of any application, where the user is able to upload their photo, their CV, or a video showcasing a project they are working on.