File uploads is a common feature for many applications and business services, however, the security complications that come with this are significant. Advanced malware can quickly evade sandboxes and bypass traditional detection methods. With businesses shifting to remote working, it’s even more crucial to apply measures to ensure file upload security.
But how can you avoid various file upload attacks? We discuss the types of file upload attacks to look out for and how you can implement file upload security to ensure that there aren’t any gaps in your protective layers.
Types of File Upload attacks
File upload attacks fall into 4 vulnerability groups. When it comes to developing a system designed to accept user-generated files, it’s vital to stay vigilant and evaluate the risks according to each group, applying security checks to avoid attacks.
1) File size attacks
Extremely large files can result in an application overload or failure. This further causes disruption of service and high consumptions of server resources and disruption for users.
2) File content attacks
Uploaded file content can contain exploits, malware and malicious scripts. An attacker can maliciously use this content to gain access to an infected users’ machine.
3) File access attacks
Attackers are easily able to manipulate the rules of a file in order to enter vulnerable systems. The file can be used to gain control of servers which can cause reputational damage and business complications.
4) File metadata attacks
An incorrect file name or path can manipulate an application into copying the file to an alternative location. Attackers can use this as a means to overwrite critical configuration files by using control characters in the file name. Another example of this would be changing security settings to upload malicious files.
How to prevent File Upload Attacks
Data protection will always be a priority across all businesses, after all, the consequences of data loss can be damaging. We’ve recommended some measures you can take in order to protect your business and its data.
1) Malware scan
To minimize risk and increase prevention, you should consider scanning all uploaded files with malware tools. We recommend using an advanced threat detection and prevention technology.
2) Verify your file types
Systems and users typically identify types of files by its extension. Attackers are able to bypass security systems by spoofing users and systems by changing file extensions. E.g. an attacker can rename a malicious .exe to .docx file, posing as a legitimate word document when in fact the file is disruptive to the user and systems. Always verify before uploading!
3) Authenticate your users
To prevent potential threats and increase your security, it's worth requiring all users to authenticate themselves before uploading a file with tools such as two-factor authentication or multi-factor authentication.
4) Randomize uploaded file names
Altering the uploaded file names prevents attackers from accessing the malicious files they uploaded. Systems such as content disarm and reconstruction (CDR) can configure the sanitized file to be a random identifier.
5) Remove embedded threats
The most common files range from Microsoft Office, PDF’s and image files which attackers can embed threats in hidden scripts and macros of files. Anti-malware software’s aren’t always reliable to detect these threats, so we recommend removing any possibilities with CDR.
6) User error messages
Setting a short and sweet error message is crucial. Error messages usually show the directory paths or server configuration settings. This type of information is what attackers can use to exploit file uploads and access your systems. Keep it simple!
7) Store your files in an external directory
Consider uploading your files to an external directory and keeping them outside the webroot. This measure will prevent hackers from executing attacks with harmful files through an assigned URL.
8) File size and length restrictions
Setting your systems to only allow a maximum size and name file length can prevent potential service outages. Where possible, it’s also worth restricting the number of allowed characters.
Looking to find out more on how to block malicious file uploads and keep your vulnerable data safe? We partner with OPSAT to bring you a robust plan to mitigate this threat vector. Our team of security experts are always available for a chat. To get started, start your free file upload security consultation today.