Browse Category: Security

Moving from Firefox ESR to Firefox Quantum, or bye RequestPolicy

When Firefox Quantum was released last fall I switched to the ESR branch, currently on v52.7.3. My main – and pretty much only – reason for not using Quantum until now was due to incompatibilites with addons not written as native WebExtensions. It’s been over six months since Quantums initial release, and as more WebExtension addons are availabe, I wanted to see if I’d be comfortable with moving on as well.

First of all, Quantum feels much faster than the old Firefox, even with a dozen enabled addons. My main concern was with RequestPolicy Continued, which I used for years to build my own whitelist in order to keep out as much browser tracking as possible. Since there is still no WebExtension port, I started exploring other addons and found that uBlock Origin is capable of everything RequestPolicy can do. I’ve used UO on Firefox before, but only as a general adblock addon with default settings. By denying any 3rd-party resources globally while using the default filter lists for blocking undesired 1st-party content, uBlock Origin has broader capabilites than RequestPolicy. Here’s a nice explanation. But since there’s no way to export my RP whitelist to UO, I had to start over – which is not as painful as I initially feared. UO is a lot more effective in building a global whitelist for Firefox. The UO github has good explanations on it’s different blocking modes.

 

Here’s what RequestPolicy Continued on Firefox ESR (52.7.3) vs. uBlock Origin in Hard Mode with Firefox 59.0.2 looks like on heise.de.

        

 

UO is globally rejecting any 3rd-party resource by default and I can create my whitelist on each website below. Note the yellow indicator, which applies the common blocklists to all 1st-party resources. In addition, I disabled web fonts globally in UO (bottom right indicator) which renders websites a little less pretty, but works for me so far.

I had no problem migrating my NoScript whitelist, since it already has a WebExtension port. A few other great privacy-related addons for Quantum include Cookie AutoDelete and Privacy Settings. There’s also an addon disabling Referrers globally, but it’s missing some functionality from RefControl, which I used before.

 

Overall, I’m happy with migrating to Firefox Quantum. It’s faster, less resource-hungry and I was able to transfer all of my privacy related workflows.

Upgrading to Debian Stretch with dovecot, postfix & opendkim

Debian Stretch is about to be released. I’m already upgrading some of my systems, and want to document a few issues I encountered after upgrading my mail server from Debian Jessie to Stretch.

 

Dovecot forgot what’s SSLv2

Before the upgrade, dovecot was configured to reject login attempts with SSLv2 & SSLv3. The corresponding line in /etc/dovecot/dovecot.conf looked like this:

ssl_protocols = !SSLv3 !SSLv2

After upgrading, logging into the mail server failed. Looking at the syslogs

dovecot: imap-login: Fatal: Invalid ssl_protocols setting: Unknown protocol 'SSLv2'

With the upgrade to Stretch and openssl 1.1.0, support vor SSLv2 was dropped entirely. Dovecot simply doesn’t recognize the argument anymore. Editing dovecot.conf helped.

ssl_protocols = !SSLv3

opendkim using file based sockets (Update 2017-10-13)

UPDATE – previous releases of opendkim on Stretch (v2.11.0) were affected by a bug, ignoring it’s own config file. See the Debian bug report.

The correct way to (re)configure the systemd daemon is to edit the default conf and regenerate the systemd config.

vi /etc/default/opendkim
# listen on loopback on port 12301:
SOCKET=inet:12301@localhost
/lib/opendkim/opendkim.service.generate
systemctl daemon-reload; systemctl restart opendkim

Tell postfix to use the TCP socket again, if nessecary.

vi /etc/postfix/main.cf
# DKIM config
milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:localhost:12301
non_smtpd_milters = inet:localhost:12301
systemctl restart postfix

This should do it.

——————————————————–

Before the upgrade, opendkim (v2.9.2) was configured as an initd service using loopback to connect to postfix.

/etc/default/opendkim

SOCKET="inet:12301@localhost" # listen on loopback on port 12301

/etc/postfix/main.cf

# DKIM config
milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:localhost:12301
non_smtpd_milters = inet:localhost:12301
root@host:~# systemctl status opendkim
opendkim.service - LSB: Start the OpenDKIM service
   Loaded: loaded (/etc/init.d/opendkim)
   Active: active (running) since Mi 2017-05-31 15:23:34 CEST; 6 days ago
  Process: 715 ExecStart=/etc/init.d/opendkim start (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/opendkim.service
           ├─791 /usr/sbin/opendkim -x /etc/opendkim.conf -u opendkim -P /var/run/opendkim/opendkim.pid
           └─796 /usr/sbin/opendkim -x /etc/opendkim.conf -u opendkim -P /var/run/opendkim/opendkim.pid

During the system upgrade, opendkim daemon was reconfigured as a native systemd daemon, which meant /etc/default/opendkim and /etc/init.d/opendkim became obsolete, even though I was asked to install the new package maintainers version of /etc/default/opendkim.

Now the opendkim (v2.11.0) systemd daemon looked like this:

opendkim.service - OpenDKIM DomainKeys Identified Mail (DKIM) Milter
   Loaded: loaded (/lib/systemd/system/opendkim.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/opendkim.service.d
           └─override.conf
   Active: active (running) since Wed 2017-06-07 13:10:15 CEST; 23s ago
 Main PID: 4806 (opendkim)
    Tasks: 7 (limit: 4915)
   CGroup: /system.slice/opendkim.service
           ├─4806 /usr/sbin/opendkim -P /var/run/opendkim/opendkim.pid -p local:/var/run/opendkim/opendkim.sock
           └─4807 /usr/sbin/opendkim -P /var/run/opendkim/opendkim.pid -p local:/var/run/opendkim/opendkim.sock

I tried editing /etc/postfix/main.cf & adding the postfix user to the opendkim group to reflect the changes:

# DKIM config
milter_protocol = 2
milter_default_action = accept
smtpd_milters = local:/var/run/opendkim/opendkim.sock
non_smtpd_milters = local:/var/run/opendkim/opendkim.sock
root@host:~# adduser postfix opendkim

Restarting opendkim & postfix, the connection still failed to work.

postfix/smtpd[4451]: warning: connect to Milter service local:/var/run/opendkim/opendkim.sock: No such file or directory

Some research revealed that postfix does chroot its process to /var/spool/postfix (didn’t know that). To reflect this, I created new subdirectories and edited the systemd daemon.

root@host:~# mkdir -p /var/spool/postfix/var/run/opendkim
root@host:~# chown -R opendkim:opendkim /var/spool/postfix/var
root@host:~# systemctl edit opendkim
[Service]
ExecStart=
ExecStart=/usr/sbin/opendkim -P /var/run/opendkim/opendkim.pid -p local:/var/spool/postfix/var/run/opendkim/opendkim.sock

Note that the double ExecStart isn’t a typo.

After restarting all affected services, my sent mails were getting a valid DKIM signature again.

opendkim[11357]: OpenDKIM Filter v2.11.0 starting (args: -P /var/run/opendkim/opendkim.pid -p local:/var/spool/postfix/var/run/opendkim/opendkim.sock)

Encrypt an existing Linux installation with LUKS and LVM

An issue I encountered recently – how to encrypt an exisiting Xubuntu Setup. There are several ways to achieve this. I want to document my process I used.

I’m working with following assumptions:

  • The Linux installation to be encrypted is the only OS on disk.
  • The system is a (X)Ubuntu or similar (Debian). Commands, paths to config files or package names might differ in other Distributions.
  • The system is EFI-enabled. This means there is a 512 MiB FAT partition at the beginning of the disk, containing the EFI loader. This partition has to remain untouched. If your system is using legacy boot, ignore instructions regarding EFI later on.
  • A Live Linux USB stick (e.g. Xubuntu 16.10) and a separate hard disk with at least the same size as the system drive are available and ready. When in doubt, use a disk which is larger than the system drive.
  • The entire process takes time.
  • Mistakes happen. Be ready to lose data from the installed system! Ideally, there are multiple recent backups in place.

Before booting from the USB linux, prepare the Linux system by installing necessary packages & latest updates.

root@host:~# apt update; apt upgrade; apt install cryptsetup pv lvm2 gparted

Remove old kernel images. This might take a while, depending on the age of the Linux installation.

root@host:~# apt autoclean; apt autoremove

Shut down the computer, connect the USB disk and the second hard drive. Boot into the live system. Make sure your keyboard layout is set accordingly.

root@live:~# dpkg-reconfigure keyboard-configuration

Install necessary packages on the live system as well.

root@live:~# apt update; apt install cryptsetup pv lvm2 gparted

Annoyingly, my live system auto-mounted the old system disk. Unmount if necessary.

Use fdisk -l to check the order of drives. In my case, sda is the old system disk, sdb is the USB stick, sdc is the second hard drive. Use dd to copy the entire system disk to the second drive, with pv monitoring progress. Don’t overwrite your system.

root@live:~# dd if=/dev/sda | pv --progress --eta --bytes --rate | dd of=/dev/sdc

When finished, open gparted and choose your system disk.

Delete the root and swap partition, create a new boot partition (512MiB, ext4, set boot / esp flags) and create a “cleared” partition from remaining available space. Leave the EFI partition untouched. Note: if there’s no EFI boot partition, format the entire disk and create partitions as described.

The result looks like this:

Consider secure erasing of the old system partition. It takes time, but leaves no trace of unencrypted data on the system drive.

root@live:~# cryptsetup open --type plain /dev/sda3 container --key-file /dev/urandom

Proceed to create the encrypted volume on the cleared partition and choose a strong password.

root@live:~# cryptsetup luksFormat -c aes-xts-plain64:sha512 -s 512 /dev/sda3

Open the encrypted volume.

root@live:~# cryptsetup luksOpen /dev/sda3 encrypted_system

Create a LVM volume group and logical volumes on top of the opened LUKS volume. Note: tempo is the name I chose. Feel free to use another name for the volume group, but keep it consistent.

root@live:~# pvcreate /dev/mapper/encrypted_system
root@live:~# vgcreate tempo /dev/mapper/encrypted_system
root@live:~# lvcreate -L 8G tempo -n swap
root@live:~# lvcreate -l 100%FREE tempo -n root

Set up the swap and root volume.

root@live:~# mkswap /dev/mapper/tempo-swap
root@live:~# mkfs.ext4 /dev/mapper/tempo-root

Mount the new root volume to /mnt.

root@live:~# mount /dev/mapper/tempo-root /mnt

Mount the old root partition, which has been copied to the second drive.

root@live:~# mount /dev/sdc3 /media/old_root/

Navigate to the old root directory and use tar to copy the root system to the new LVM volume. The command doesn’t compress file input but redirects it to stdout. The output is then piped to the 2nd command where tar reads it from stdin. This way, all file & system attributes are preserved.

root@live:~# cd /media/old_root/
root@live:~# tar cvf - . | tar xf - -C /mnt/

When finished, delete all contents from the boot directory, since this will be the mount point for the new boot partition. Use the piped tar command to copy contents from the second drive. Mount the EFI partiton as well.

root@live:~# rm -rf /mnt/boot/*
root@live:~# mount /dev/sda2 /mnt/boot
root@live:~# cd /media/old_root/boot/
root@live:~# tar cvf - . | tar xf - -C /mnt/boot/
root@live:~# mount /dev/sda1 /mnt/boot/efi

Get the UUID of the encrypted LUKS volume. We need this later on.

root@live:~# blkid /dev/sda3
/dev/sda3: UUID="0f348572-6937-410f-8e04-1b760d5d11fe" TYPE="crypto_LUKS" PARTUUID="85f58482-8b18-446a-8cb6-cfdfe30c7d55"

Prepare the new root system in /mnt for chroot.

root@live:~# for dir in /dev /dev/pts /proc /sys /run; do mount --bind $dir /mnt/$dir; done
root@live:~# chroot /mnt

In the chrooted environment, we need to create or edit several config files to tell Linux where to look for the LVM swap / root volumes and how to open them. Create /etc/crypttab with the name of the volume group (tempo in my case) and the LUKS UUID we got earlier.

# 				
encrypted_system  UUID=0f348572-6937-410f-8e04-1b760d5d11fe  none  luks,discard,lvm=tempo

Create a file named /etc/initramfs-tools/conf.d/cryptroot in the chrooted environment. Replace tempo with the name used to open the LUKS volume and the UUID of the LUKS partition.

CRYPTROOT=target=tempo-root,source=/dev/disk/by-uuid/0f348572-6937-410f-8e04-1b760d5d11fe

Run the follwing command in the chrooted environment. It should pass without issues.

root@live:~# update-initramfs -k all -c

Open /etc/default/grub in the chrooted environment. Find this line:

GRUB_CMDLINE_LINUX=""

Insert the appropriate values (volume group name, LUKS UUID):

GRUB_CMDLINE_LINUX="cryptops=target=tempo-root,source=/dev/disk/by-uuid/0f348572-6937-410f-8e04-1b760d5d11fe,lvm=tempo"

Update grub in the chrooted environment. It will read arguments from /etc/default/grub and create new boot entries.

root@live:~# update-grub

Open /etc/fstab in the chrooted environment. Update the entry for the encrypted root and swap volume. Use blkid to find the UUID of the new boot partition. Leave the EFI partition entry untouched. My new fstab looks like this:

UUID=2886e598-0d5c-4576-87e7-a234011e7725	/boot		ext4	defaults		0	2
UUID=E2F4-2888					/boot/efi	vfat	umask=0077		0	3
/dev/mapper/tempo-root				/		ext4	errors=remount-ro	0	1
/dev/mapper/tempo-swap				none		swap	sw			0	0

That’s it. Close the chrooted environment and shut down the computer. Remove the USB stick and second hard drive. A password prompt should appear during boot. If everything goes well, the newly encrypted system will boot. Check if all partitions are mounted accordingly. Reboot again to check if recovery mode is working as well. Note that you still have an exact copy of your system previous to encryption on the second hard drive. After verifying the encrypted system is working as intended, you might want to consider secure erasing secure erasing of the unencrypted disk.

PGP key generation – increase system entropy

While creating a new PGP key pair using Enigmail, the progress bar seems stuck, and there’s no CPU activity.

The problem – missing entropy for /dev/random. Take a look at the available kernel entropy:

user@host:~# watch -n 0.2 cat /proc/sys/kernel/random/entropy_avail

If the number stays below – say – 300, PGP can’t find enough random data through /dev/random and won’t generate keys. There’s still /dev/urandom, which Engimail/PGP apparently ignores. So in order to generate acceptable levels of entropy for /dev/random and Engimail, I’m installing haveged, a “random number generator feeding Linux’s random device”.

user@host:~# sudo apt install haveged
user@host:~# sudo systemctl enable haveged.service
user@host:~# sudo systemctl start haveged.service

Now my system’s availabe entropy is at 1800, enough for Enigmail to generate my PGP keys.

Erasing hard disks fast & securely with OpenSSL

Erasing & overwriting disks with dd can take a very long time, both with /dev/null and /dev/urandom. Most modern CPUs are capable of AES-NI, accelerating cryptographic operations while reducing system load dramatically. That’s why I’m using OpenSSL to erase my disk drives. The advantages are clear – encrypted pseudorandom data output and maximum I/O throughput. Studies have shown that one wipe is sufficient on magnetic HDDs.

 

openssl enc -aes-256-ctr -pass pass:"$(dd if=/dev/urandom bs=128 count=1 </dev/null | base64)" -nosalt </dev/zero | pv --progress --eta --rate --bytes | dd of=/dev/sdX

 

Replace sdX with the target drive. Make sure pv is installed before executing. OpenSSL is encrypting /dev/zero with a randomized password of /dev/urandom. You should see a progress bar & ETA.