How does your encrypted Linux system respond to the Cryptsetup bug?

The news making the rounds in the Linux security arena is the one about a bug discovered in Cryptsetup, the program used to set up disk encryption in Linux.

The bug, detailed here, was discovered by Hector Marco and Ismael Ripoll.

As described by the authors, the bug is basically the result of incorrect error handling after several failed attempts to decrypt a LUKS encrypted disk. And the failure could be triggered when a user inputs the wrong encryption passphrase, or repeatedly presses the ENTER key.

In their report, they noted that:

An attacker with access to the console of the computer and with the ability to reboot the computer can launch a shell (with root permissions) when he/she is prompted for the password to unlock the system partition. The shell is executed in the initrd environment. Obviously, the system partition is encrypted and it is not possible to decrypt it (AFAWK). But other partitions may be not encrypted, and so accessible. Just to mention some exploitation strategies:

Their report appears to be based on tests of Debian and Ubuntu systems. From my own experience, I can report that every major distribution seems to handle failed hard disk decryption a bit differently. To start with Ubuntu, the system will drop to an initramfs shell after 181 failed attempts (you can simulated it by pressing the ENTER key that many times). If you have such a system, give it a try. After 181 failed attempts, you’ll be presented with a shell like the one shown in Figure 1.

Decrypt Ubuntu 16.10 system partition
Figure 1: Result of failed attempt to decrypt Ubuntu 16.10 system partition

With Fedora 25 Rawhide, you have just three attempts before the system gives you a shell. And that has been the case with Fedora systems for as long as I can remember. Compare that to the 181 attempts on Ubuntu 16.10.

Decrypt Fedora 25 Rawhide system partition
Figure 2: Result of failed attempt to decrypt Fedora 25 Rawhide system partition

Manjaro 16.10, which uses the Calamares installer, is even less forgiving. It gives you just one attempt before it drops you into a shell.

Decrypt Manjaro 16.10 system partition
Figure 3: Result of failed attempt to decrypt Manjaro 16.10 system partition

In all three case, the encrypted system partition is still encrypted, so you data is still save. However, as detailed in the bug report, unencrypted partitions, like ones mounted at /boot and /boot/efi (on UEFI systems) might still be open for exploitation. But how far can an attacker go on such system, when the system partition is still encrypted? Not far, I hope.

Related Post:  How to backup your Linux files to a Minio storage server using CloudBerry Backup

A bug always has a solution, and in this case, the authors provided an easy-to-apply workaround. I’ve expanded on it a bit in the code block below. If after applying the workaround you discover that it does not work, welcome to the club. It didn’t work on all the encrypted systems I applied it on – Ubuntu 16.10, Manjaro 16.10, and Fedora Rawhide. By the way, all three distributions were running either Cryptsetup 1.7.2 or 1.7.3.

Related Post:  Dual-booting Windows and Linux: Why and how

If the workaround stopped your system from dropping into a shell on failed decryption attempts, which means it worked, post a comment. I’ve contact the authors with my findings, so I’ll update this article when I get some feedback from them. Perhaps there’s something I missed.

Subscribe to LinuxBSDos.com

Subscribe to receive the latest articles in your Inbox

Trust me, you'll not be spammed...

Please share:

We Recommend These Vendors and Free Offers

Register now for Blockchain & Cryptocurrency Con 2018, international conference on blockchain technnology in Dallas, TX (USA), Feb. 23-24, 2018. A 50% discount for students.

Best WhatsApp Plus features in Gbwhatsapp latest APK download

Best binary auto trading software reviews by 7binaryoptions.com

Google has got competition, because Presearch is building a blockchain-based search engine controlled by the community. At $0.15 a token, you can participation in Lot 3 of the token sale by clicking here

Open Money is building a solution that will run mainstream software on blockchain tech. Click here to get free tokens that will be the digital currency of the platform

Launch an SSD VPS in Europe, USA, Asia & Australia on Vultr's KVM-based Cloud platform starting at $5:00/month (15 GB SSD, 768 MB of RAM).


  1. Hi,

    I think i found a workaround on Fedora.
    You can add the rd.shell=0 option to your Grub command line to disable the dracut shell.

    – Edit the /etc/grub2.cfg file
    – Add rd.shell=0 to the /vmlinuz… line
    – Reboot and test it

    That works for me.


Leave a Comment

Your email address will not be published. Required fields are marked *