A vulnerability in cryptsetup, a utility used to set up encrypted filesystems on Linux distributions, could allow an attacker to retrieve a root rescue shell on some systems. From there, an attacker could have the ability to copy, modify, or destroy a hard disk, or use the network to exfiltrate data.
Cryptsetup, a utility used to setup disk encryption based on the dm-crypt kernel module, is usually deployed in Debian and Ubuntu. Researchers warned late last week that if anyone uses the tool to encrypt system partitions for the operating systems, they’re likely vulnerable.
Two researchers, Hector Marco of the University of the West of Scotland and Ismael Ripoll, of the Polytechnic University of Valencia, in Spain, disclosed the vulnerability on Friday at DeepSec, a security conference held at the Imperial Riding School Renaissance Vienna Hotel in Austria.
According to the researchers, the script with the vulnerability (CVE-2016-4484) is in the Debian cryptsetup package 2:1.7.2-3 and earlier. Systems that use Dracut, an infrastructure commonly deployed on Fedora in lieu of initramfs – a simple RAM file system directory, are also vulnerable, according to the researchers. The pair say additional Linux distributions outside of Debian and Ubuntu may be vulnerable, they just haven’t tested them yet.
The problem stems from the incorrect handling of a password check when a partition is ciphered with LUKS, or Linux Unified Key Setup, a disk encryption specification that’s standard for Linux.
Assuming an attacker has access to the computer’s console, when presented with the LUKS password prompt, they could exploit the vulnerability simply by pressing ‘Enter’ over and over again until a shell appears. The researchers say the exploit could take as few as 70 seconds.
After a user exceeds the maximum number of three password tries, the boot sequence continues normally. Another script in the utility doesn’t realize this, and drops a BusyBox shell. After carrying out the exploit, the attacker could obtain a root initramfs, or rescue shell. Since the shell can be executed in the initrd, or initial ram disk, environment, it can lead to a handful of scary outcomes, including elevation of privilege, information disclosure, or denial of service.
The researchers warn that the vulnerability is especially dangerous in public situations. “This vulnerability is specially serious in environments like libraries, ATMs, airport machines, labs, etc, where the whole boot process is protect (password in BIOS and GRUB) and we only have a keyboard or/and a mouse,” the vulnerability disclosure reads.
All an attacker would need in those instances – assuming the system is running Linux – would be access to the keyboard or mouse, Marco and Ripoll say. Tourist information kiosks or airport check in kiosks could be prime targets, the two write.
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