security-misc/README.md

# 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_security-misc.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/modprobe.d/30_security-misc.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.

* Avoids unintentional writes to attacker-controlled files.

* Prevents symlink/hardlink TOCTOU races.

* SACK can be disabled as it is commonly exploited and is rarely used by
uncommenting settings in file `/etc/sysctl.d/30_security-misc.conf`.

* Slab merging is disabled as sometimes a slab can be used in a vulnerable
way which an attacker can exploit.

* Sanity checks and redzoning are enabled.

* Memory zeroing at allocation and free time is enabled.

* The machine check tolerance level is decreased 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.

* Enables all mitigations for CPU vulnerabilities and disables SMT.

* 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/30_security-misc.conf`
`/etc/sysctl.d/30_security-misc.conf`
`/lib/systemd/coredump.conf.d/30_security-misc.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.

* 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
`/etc/modprobe.d/30_security-misc.conf`

* 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.
`/usr/lib/security-misc/hide-hardware-info`
`/lib/systemd/system/hide-hardware-info.service`
`/lib/systemd/system/user@.service.d/sysfs.conf`
`/etc/hide-hardware-info.d/30_default.conf`

* The MSR kernel module is blacklisted to prevent CPU MSRs from being
abused to write to arbitrary memory.

* Vsyscalls are disabled as they are obsolete, are at fixed addresses and are
a target for ROP.

* Page allocator freelist randomization is enabled.

* The vivid kernel module is blacklisted as it's only required for testing
and has been the cause of multiple vulnerabilities.

* An initramfs hook sets the sysctl values in `/etc/sysctl.conf` and
`/etc/sysctl.d` before init is executed so sysctl hardening is enabled
as early as possible.

* The kernel panics on oopses to prevent it from continuing to run a flawed
process and to deter brute forcing.

* Restricts the SysRq key so it can only be used for shutdowns and the
Secure Attention Key.

* Restricts loading line disciplines to `CAP_SYS_MODULE`.

* Restricts the `userfaultfd()` syscall to 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`

* Gathers more entropy during boot if using the linux-hardened kernel patch.

Uncommon network protocols are blacklisted:
These are rarely used and may have unknown vulnerabilities.
`/etc/modprobe.d/30_security-misc.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 console.
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) Using pam_access.
Not enabled by default in this package since this package does not know which
users shall be added to group 'console' and would break console.
`/usr/share/pam-configs/console-lockdown-security-misc`
`/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 `mkhomedir`. 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/lib/security-misc/permission-lockdown`
`/usr/share/pam-configs/mkhomedir-security-misc`

* SUID / GUID removal and permission hardening.
A systemd service removed SUID / GUID from non-essential binaries as these are
often used in privilege escalation attacks.
It is disabled by default for now during testing and can optionally be enabled
by running `systemctl enable permission-hardening.service` as root.
https://forums.whonix.org/t/disable-suid-binaries/7706
`/usr/lib/security-misc/permission-hardening`
`/lib/systemd/system/permission-hardening.service`
`/etc/permission-hardening.d/30_default.conf`

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 rescue and emergency shell.
This is the same solution that Debian will likely adapt 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/30_security-misc.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.
`/usr/share/glib-2.0/schemas/30_security-misc.gschema.override`
* Deactivates thumbnails in Thunar.
* Enables punycode (`network.IDN_show_punycode`) by default in Thunderbird
to make phishing attacks more difficult. Fixing URL not showing real Domain
Name (Homograph attack).

Want more? Look into these:

* Linux Kernel Runtime Guard (LKRG)
* tirdad - TCP ISN CPU Information Leak Protection.
* Whonix ™ - Anonymous Operating System
* Kicksecure ™ - A Security-hardened, Non-anonymous Linux Distribution
* SecBrowser ™ - A Security-hardened, Non-anonymous Browser
* And more.
* https://www.whonix.org/wiki/Linux_Kernel_Runtime_Guard_LKRG
* https://github.com/Whonix/tirdad
* https://www.whonix.org
* https://www.whonix.org/wiki/Kicksecure
* https://www.whonix.org/wiki/SecBrowser
* https://github.com/Whonix

Discussion:

Happening primarily in Whonix forums.
https://forums.whonix.org/t/kernel-hardening/7296
## 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](https://www.whonix.org/wiki/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](https://www.whonix.org/wiki/Dev/Build_Documentation/apparmor-profile-torbrowser).

## Contact ##

* [Free Forum Support](https://forums.whonix.org)
* [Professional Support](https://www.whonix.org/wiki/Professional_Support)

## Donate ##

`security-misc` requires [donations](https://www.whonix.org/wiki/Donate) to stay alive!