‘Less’ means more to malware authors targeting Linux users

Using the “less” Linux command to view the contents of files downloaded from the Internet is a dangerous operation that can lead to remote code execution, according to a security researcher.

At first glance, less appears to be a harmless command that outputs a file’s content to a terminal window and allows the users to navigate forward and backward through it. Less does not allow file editing, which is a job for file editors like the widely used vi, but has the benefit of displaying data on the fly without needing to load an entire file into memory. This is useful when dealing with large files.

Less is frequently used to view text files, but on many Linux distributions, including Ubuntu and CentOS, it supports many more file types including archives, images and PDF. That’s because, on these systems, less is extended through a script called lesspipe that relies on different third-party tools to process files with various extensions.

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