enhances misc security settings

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 /proc/kallsyms are hidden to prevent malware from reading them and using them to learn more about what to attack on your system.

• Kexec is disabled as it can be used for live patching of the running kernel.

• ASLR effectiveness for mmap is increased.

• The TCP/IP stack is hardened.

• This package makes some data spoofing attacks harder.

• SACK is disabled as it is commonly exploited and is rarely used.

• This package disables the merging of slabs of similar sizes to prevent an attacker from exploiting them.

• Sanity checks, redzoning, and memory poisoning are enabled.

• The kernel now panics on uncorrectable errors in ECC memory which 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 vulnerability.

• All mitigations for the MDS vulnerability are enabled.

• The SysRq key is restricted to only allow shutdowns/reboots. /etc/sysctl.d/sysrq.conf

• 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 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

• Requires every module to be signed before being loaded. Any module that is unsigned or signed with an invalid key cannot be loaded. This makes it harder to load a malicious module. /etc/default/grub.d/40_only_allow_signed_modules.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:

• 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

• Lock user accounts after 100 failed login attempts using pam_tally2. /usr/share/pam-configs/tally2-security-misc

• 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

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:

• 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:

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.

How to install security-misc using apt-get

1. Download Whonix's Signing Key.

wget https://www.whonix.org/patrick.asc

Users can check Whonix Signing Key for better security.

2. Add Whonix's signing key.

sudo apt-key --keyring /etc/apt/trusted.gpg.d/whonix.gpg add ~/patrick.asc

3. Add Whonix's APT repository.

echo "deb https://deb.whonix.org buster main contrib non-free" | sudo tee /etc/apt/sources.list.d/whonix.list

4. Update your package lists.

sudo apt-get update

5. Install security-misc.

sudo apt-get install security-misc

How to Build deb Package

Replace apparmor-profile-torbrowser with the actual name of this package with security-misc and see instructions.

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