security-misc/debian/control

## Copyright (C) 2012 - 2019 ENCRYPTED SUPPORT LP <adrelanos@riseup.net>
## See the file COPYING for copying conditions.

Source: security-misc
Section: misc
Priority: optional
Maintainer: Patrick Schleizer <adrelanos@riseup.net>
Build-Depends: debhelper (>= 12), genmkfile, config-package-dev, dh-apparmor
Homepage: https://github.com/Whonix/security-misc
Vcs-Browser: https://github.com/Whonix/security-misc
Vcs-Git: https://github.com/Whonix/security-misc.git
Standards-Version: 4.3.0

Package: security-misc
Architecture: all
Depends: python, libglib2.0-bin, libpam-runtime, sudo, adduser,
 apparmor-profile-anondist, ${misc:Depends}
Replaces: tcp-timestamps-disable
Description: enhances misc security settings
 Inspired by Kernel Self Protection Project (KSPP)
 .
  * Implements most if not all recommended Linux kernel settings (sysctl) and
 kernel parameters by KSPP.
 .
  * https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project
 .
 kernel hardening:
 .
  * deactivates Netfilter's connection tracking helper
 Netfilter's connection tracking helper module increases kernel attack
 surface by enabling superfluous functionality such as IRC parsing in
 the kernel. (!) Hence, this package disables this feature by shipping the
 /etc/modprobe.d/30_nf_conntrack_helper_disable.conf configuration file.
 .
  * Kernel symbols in various files in /proc are hidden as they can be
 very useful for kernel exploits.
 .
  * Kexec is disabled as it can be used to load a malicious kernel.
 /etc/sysctl.d/kexec.conf
 .
  * ASLR effectiveness for mmap is increased.
 .
  * The TCP/IP stack is hardened by disabling ICMP redirect acceptance,
 ICMP redirect sending and source routing to prevent man-in-the-middle attacks,
 ignoring all ICMP requests, enabling TCP syncookies to prevent SYN flood
 attacks, enabling RFC1337 to protect against time-wait assassination
 attacks and enabling reverse path filtering to prevent IP spoofing and
 mitigate vulnerabilities such as CVE-2019-14899.
 .
  * Some data spoofing attacks are made harder.
 .
  * SACK can be disabled as it is commonly exploited and is rarely used by
 uncommenting settings in file /etc/sysctl.d/tcp_sack.conf.
 .
  * Slab merging is disabled as sometimes a slab can be used in a vulnerable
 way which an attacker can exploit.
 .
  * Sanity checks, redzoning, and memory poisoning are enabled.
 .
  * Machine checks (MCE) are disabled which makes the kernel panic
 on uncorrectable errors in ECC memory that could be exploited.
 .
  * Kernel Page Table Isolation is enabled to mitigate Meltdown and increase
 KASLR effectiveness.
 .
  * SMT is disabled as it can be used to exploit the MDS and other
 vulnerabilities.
 .
  * All mitigations for the MDS vulnerability are enabled.
 .
  * A systemd service clears System.map on boot as these contain kernel symbols
 that could be useful to an attacker.
 /etc/kernel/postinst.d/30_remove-system-map
 /lib/systemd/system/remove-system-map.service
 /usr/lib/security-misc/remove-system.map
 .
  * Coredumps are disabled as they may contain important information such as
 encryption keys or passwords.
 /etc/security/limits.d/disable-coredumps.conf
 /etc/sysctl.d/coredumps.conf
 /lib/systemd/coredump.conf.d/disable-coredumps.conf
 .
  * The thunderbolt and firewire kernel modules are blacklisted as they can be
 used for DMA (Direct Memory Access) attacks.
 .
  * IOMMU is enabled with a boot parameter to prevent DMA attacks.
 .
  * The kernel now panics on oopses to prevent it from continuing running a
 flawed process.
 .
  * Bluetooth is blacklisted to reduce attack surface. Bluetooth also has
 a history of security concerns.
 https://en.wikipedia.org/wiki/Bluetooth#History_of_security_concerns
 .
  * A systemd service restricts /proc/cpuinfo, /proc/bus, /proc/scsi and
 /sys to the root user only. This hides a lot of hardware identifiers from
 unprivileged users and increases security as /sys exposes a lot of information
 that shouldn't be accessible to unprivileged users. As this will break many
 things, it is disabled by default and can optionally be enabled by running
 `systemctl enable hide-hardware-info.service` as root.
 .
 Improve Entropy Collection
 .
  * Load jitterentropy_rng kernel module.
  /usr/lib/modules-load.d/30_security-misc.conf
 .
  * Distrusts the CPU for initial entropy at boot as it is not possible to
  audit, may contain weaknesses or a backdoor.
    * https://en.wikipedia.org/wiki/RDRAND#Reception
    * https://twitter.com/pid_eins/status/1149649806056280069
    * For more references, see:
    * /etc/default/grub.d/40_distrust_cpu.cfg
 .
 Uncommon network protocols are blacklisted:
 These are rarely used and may have unknown vulnerabilities.
 /etc/modprobe.d/uncommon-network-protocols.conf
 The network protocols that are blacklisted are:
 .
  * DCCP - Datagram Congestion Control Protocol
  * SCTP - Stream Control Transmission Protocol
  * RDS - Reliable Datagram Sockets
  * TIPC - Transparent Inter-process Communication
  * HDLC - High-Level Data Link Control
  * AX25 - Amateur X.25
  * NetRom
  * X25
  * ROSE
  * DECnet
  * Econet
  * af_802154 - IEEE 802.15.4
  * IPX - Internetwork Packet Exchange
  * AppleTalk
  * PSNAP - Subnetwork Access Protocol
  * p8023 - Novell raw IEEE 802.3
  * p8022 - IEEE 802.2
 .
 user restrictions:
 .
  * remount /home, /tmp, /dev/shm and /run with nosuid,nodev (default) and
 noexec (opt-in). To disable this, run "sudo touch /etc/remount-disable". To
 opt-in noexec, run "sudo touch /etc/noexec" and reboot (easiest).
 Alternatively file /usr/local/etc/remount-disable or file
 /usr/local/etc/noexec could be used.
 /lib/systemd/system/remount-secure.service
 /usr/lib/security-misc/remount-secure
 .
  * A systemd service mounts /proc with hidepid=2 at boot to prevent users from
 seeing each other's processes.
 .
  * The kernel logs are restricted to root only.
 .
  * The BPF JIT compiler is restricted to the root user and is hardened.
 .
  * The ptrace system call is restricted to the root user only.
 .
 restricts access to the root account:
 .
  * `su` is restricted to only users within the group `sudo` which prevents
 users from using `su` to gain root access or to switch user accounts.
 /usr/share/pam-configs/wheel-security-misc
 (Which results in a change in file `/etc/pam.d/common-auth`.)
 .
 * Add user `root` to group `sudo`. This is required to make above work so
 login as a user in a virtual console is still possible.
 debian/security-misc.postinst
 .
  * Abort login for users with locked passwords.
 /usr/lib/security-misc/pam-abort-on-locked-password
 .
  * Logging into the root account from a virtual, serial, whatnot console is
 prevented by shipping an existing and empty /etc/securetty.
 (Deletion of /etc/securetty has a different effect.)
 /etc/securetty.security-misc
 .
  * Console Lockdown.
 Allow members of group 'console' to use tty1 to tty7. Everyone else except
 members of group 'console-unrestricted' are restricted from using console
 using ancient, unpopular login methods such as using /bin/login over networks,
 which might be exploitable. (CVE-2001-0797)
 Not enabled by default in this package since this package does not know which
 users shall be added to group 'console'.
 In new Whonix builds, user 'user" will be added to group 'console' and
 pam console-lockdown enabled by package anon-base-files.
 /usr/share/pam-configs/console-lockdown
 /etc/security/access-security-misc.conf
 .
 Protect Linux user accounts against brute force attacks.
 Lock user accounts after 50 failed login attempts using pam_tally2.
 /usr/share/pam-configs/tally2-security-misc
 .
 informational output during Linux PAM:
 .
  * Show failed and remaining password attempts.
  * Document unlock procedure if Linux user account got locked.
  * Point out, that there is no password feedback for `su`.
  * Explain locked (root) account if locked.
  * /usr/share/pam-configs/tally2-security-misc
  * /usr/lib/security-misc/pam_tally2-info
  * /usr/lib/security-misc/pam-abort-on-locked-password
 .
 access rights restrictions:
 .
  * Strong Linux User Account Separation.
 Removes read, write and execute access for others for all users who have
 home folders under folder /home by running for example
 "chmod o-rwx /home/user"
 during package installation, upgrade or pam. This will be done only once per
 folder in folder /home so users who wish to relax file permissions are free to
 do so. This is to protect previously created files in user home folder which
 were previously created with lax file permissions prior installation of this
 package.
 debian/security-misc.postinst
 /usr/share/pam-configs/permission-lockdown-security-misc
 /usr/lib/security-misc/permission-lockdown
 .
 access rights relaxations:
 .
 Redirect calls for pkexec to lxqt-sudo because pkexec is incompatible with
 hidepid.
 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=860040
 https://forums.whonix.org/t/cannot-use-pkexec/8129
 /usr/bin/pkexec.security-misc
 .
 This package does (not yet) automatically lock the root account password.
 It is not clear that would be sane in such a package.
 It is recommended to lock and expire the root account.
 In new Whonix builds, root account will be locked by package
 anon-base-files.
 https://www.whonix.org/wiki/Root
 https://www.whonix.org/wiki/Dev/Permissions
 https://forums.whonix.org/t/restrict-root-access/7658
 However, a locked root password will break rescue and emergency shell.
 Therefore this package enables passwordless resuce and emergency shell.
 This is the same solution that Debian will likely addapt for Debian
 installer.
 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=802211
 Adverse security effects can be prevented by setting up BIOS password
 protection, grub password protection and/or full disk encryption.
 /etc/systemd/system/emergency.service.d/override.conf
 /etc/systemd/system/rescue.service.d/override.conf
 .
 Disables TCP Time Stamps:
 .
 TCP time stamps (RFC 1323) allow for tracking clock
 information with millisecond resolution. This may or may not allow an
 attacker to learn information about the system clock at such
 a resolution, depending on various issues such as network lag.
 This information is available to anyone who monitors the network
 somewhere between the attacked system and the destination server.
 It may allow an attacker to find out how long a given
 system has been running, and to distinguish several
 systems running behind NAT and using the same IP address. It might
 also allow one to look for clocks that match an expected value to find the
 public IP used by a user.
 .
 Hence, this package disables this feature by shipping the
 /etc/sysctl.d/tcp_timestamps.conf configuration file.
 .
 Note that TCP time stamps normally have some usefulness. They are
 needed for:
 .
  * the TCP protection against wrapped sequence numbers; however, to
   trigger a wrap, one needs to send roughly 2^32 packets in one
   minute:  as said in RFC 1700, "The current recommended default
   time to live (TTL) for the Internet Protocol (IP) [45,105] is 64".
   So, this probably won't be a practical problem in the context
   of Anonymity Distributions.
  * "Round-Trip Time Measurement", which is only useful when the user
   manages to saturate their connection. When using Anonymity Distributions,
   probably the limiting factor for transmission speed is rarely the capacity
   of the user connection.
 .
 Application specific hardening:
 .
  * Enables APT seccomp-BPF sandboxing. /etc/apt/apt.conf.d/40sandbox
  * Deactivates previews in Dolphin.
  * Deactivates previews in Nautilus.
  * Deactivates thumbnails in Thunar.
  * Enables punycode (`network.IDN_show_punycode`) by default in Thunderbird
   to make phising attacks more difficult. Fixing URL not showing real Domain
   Name (Homograph attack).
 .
 Discussion:
 .
 Happening primarily in Whonix forums.
 https://forums.whonix.org/t/kernel-hardening/7296