How to Bypass Authentication on a Linux System

Nov 16, 2016

Major bug affects Debian/Ubuntu distributions.

Researchers have discovered a flaw in the Cryptsetup utility that allows an attacker to bypass the authentication process on some Linux-based systems just by pressing and holding the Enter key for 70 seconds.

Debian/Ubuntu-based systems with encrypted system partitions are affected by this vulnerability. Researchers warn that other distributions using Dracut instead of initramfs are also vulnerable.

Hector Marco and Ismael Ripoll from the Cybersecurity Group explained in their security advisory that the vulnerability allows you to obtain a root initramfs shell on the affected system. “The vulnerability is very reliable because it doesn't depend on specific systems or configurations. Attackers can copy, modify, or destroy the hard disk as well as setup the network to exfiltrate data. This vulnerability is especially serious in environments like libraries, ATMs, airport machines, labs, etc, where the whole boot process is protected (password in BIOS and GRUB) and you only have a keyboard and/or a mouse,” Marco and Ripol wrote.

The worst thing about this vulnerability is that you don’t need physical access to the machine; it is possible to exploit the vulnerability remotely in cloud environments.

Last year, the same researchers discovered a bug in GRUB 2 that allowed an attacker to bypass all securities on a locked-down Linux machine by hitting the Enter key 28 times when asked for a user name.

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