Enhances miscellaneous security settings
This section is inspired by the Kernel Self Protection Project (KSPP). It implements all recommended Linux kernel settings by the KSPP and many more.
sysctl settings are configured via the
A kernel pointer points to a specific location in kernel memory. These can be very useful in exploiting the kernel so they are restricted to
The kernel logs are restricted to
CAP_SYSLOGas they can often leak sensitive information such as kernel pointers.
ptrace()system call is restricted to
eBPF is restricted to
CAP_SYS_ADMINon kernel versions prior to 5.8) and JIT hardening techniques such as constant blinding are enabled.
Restricts performance events to
CAP_SYS_ADMINon kernel versions prior to 5.8).
Restricts loading line disciplines to
CAP_SYS_MODULEto prevent unprivileged attackers from loading vulnerable line disciplines with the
TIOCSETDioctl which has been abused in a number of exploits before.
userfaultfd()is often abused to exploit use-after-free flaws.
Kexec is disabled as it can be used to load a malicious kernel and gain arbitrary code execution in kernel mode.
Randomises the addresses for mmap base, heap, stack, and VDSO pages.
Prevents unintentional writes to attacker-controlled files.
Prevents common symlink and hardlink TOCTOU races.
Restricts the SysRq key so it can only be used for shutdowns and the Secure Attention Key.
The kernel is only allowed to swap if it is absolutely necessary. This prevents writing potentially sensitive contents of memory to disk.
TCP timestamps are disabled as it can allow detecting the system time.
- The bits of entropy used for mmap ASLR are maxed out via
/usr/libexec/security-misc/mmap-rnd-bits(set to the values of
CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAXthat the kernel was built with), therefore improving its effectiveness.
Boot parameters are outlined in configuration files located in the
Slab merging is disabled which significantly increases the difficulty of heap exploitation by preventing overwriting objects from merged caches and by making it harder to influence slab cache layout.
Memory zeroing at allocation and free time is enabled to mitigate some use-after-free vulnerabilities and erase sensitive information in memory.
Page allocator freelist randomization is enabled.
Kernel Page Table Isolation is enabled to mitigate Meltdown and increase KASLR effectiveness.
vsyscalls are disabled as they are obsolete, are at fixed addresses and thus, are a potential target for ROP.
The kernel panics on oopses to thwart certain kernel exploits.
Enables randomisation of the kernel stack offset on syscall entries.
All mitigations for known CPU vulnerabilities are enabled and SMT is disabled.
IOMMU is enabled to prevent DMA attacks along with strict enforcement of IOMMU TLB invalidation so devices will never be able to access stale data contents.
Distrust the 'randomly' generated CPU and bootloader seeds.
Disables and blacklists kernel modules
Certain kernel modules are disabled and blacklisted by default to reduce attack surface via the
/etc/modprobe.d/30_security-misc.conf configuration file.
Deactivates Netfilter's connection tracking helper - this module increases kernel attack surface by enabling superfluous functionality such as IRC parsing in the kernel. Hence, this feature is disabled.
Bluetooth is disabled to reduce attack surface. Bluetooth has a lengthy history of security concerns.
Thunderbolt and numerous FireWire kernel modules are also disabled as they are often vulnerable to DMA attacks.
The MSR kernel module is disabled to prevent CPU MSRs from being abused to write to arbitrary memory.
Uncommon network protocols are blacklisted. This includes:
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
af_802154 - IEEE 802.15.4
IPX - Internetwork Packet Exchange
PSNAP - Subnetwork Access Protocol
p8023 - Novell raw IEEE 802.3
p8022 - IEEE 802.2
CAN - Controller Area Network
Disables a large array of uncommon file systems and network file systems that reduces the attack surface especially against legacy approaches.
The vivid kernel module is only required for testing and has been the cause of multiple vulnerabilities so it is disabled.
Provides some disabling of the interface between the Intel Management Engine (ME) and the OS.
Incorporates much of Ubuntu's default blacklist of modules to be blocked from automatically loading. However, they are still permitted to load.
Blocks automatic loading of the modules needed to use of CD-ROM devices by default. Not completely disabled yet.
- A systemd service clears the System.map file on boot as these contain kernel pointers. The file is completely overwritten with zeroes to ensure it cannot be recovered. See:
- Coredumps are disabled as they may contain important information such as encryption keys or passwords. See:
- An initramfs hook sets the sysctl values in
/etc/sysctl.dbefore init is executed so sysctl hardening is enabled as early as possible. This is implemented for
initramfs-toolsonly because this is not needed for
dracutdoes that by default, at least on
systemdenabled systems. Not researched for non-
systemdsystems by the author of this part of the readme.
TCP syncookies are enabled to prevent SYN flood attacks.
ICMP redirect acceptance, ICMP redirect sending, source routing and IPv6 router advertisements are disabled to prevent man-in-the-middle attacks.
The kernel is configured to ignore all ICMP requests to avoid Smurf attacks, make the device more difficult to enumerate on the network and prevent clock fingerprinting through ICMP timestamps.
RFC1337 is enabled to protect against time-wait assassination attacks by dropping RST packets for sockets in the time-wait state.
Reverse path filtering is enabled to prevent IP spoofing and mitigate vulnerabilities such as CVE-2019-14899.
Entropy collection improvements
jitterentropy_rngkernel module is loaded as early as possible during boot to gather more entropy via the
Distrusts the CPU for initial entropy at boot as it is not possible to audit, may contain weaknesses or a backdoor. For references, see:
Gathers more entropy during boot if using the linux-hardened kernel patch.
Restrictive mount options
Not enabled by default yet. In development. Help welcome.
/run are remounted with the
mount options to prevent execution of setuid or setgid binaries and creation of
devices on those filesystems.
Optionally, they can also be mounted with
noexec to prevent execution of any
binary. To opt-in to applying
touch /etc/noexec as root
To disable this, execute
touch /etc/remount-disable as root.
could be used.
Root access restrictions
suis restricted to only users within the group
sudowhich prevents users from using
suto gain root access or to switch user accounts -
/usr/share/pam-configs/wheel-security-misc(which results in a change in file
sudo. This is required due to the above restriction so that logging in from a virtual console is still possible -
Abort login for users with locked passwords -
Logging into the root account from a virtual, serial, whatnot console is prevented by shipping an existing and empty
/etc/securettyfile (deletion of
/etc/securettyhas a different effect).
This package does not yet automatically lock the root account password. It is not clear if this would be sane in such a package although, it is recommended to lock and expire the root account.
In new Kicksecure builds, root account will be locked by package dist-base-files.
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.
This uses pam_access to allow members of group
console to use console but
restrict everyone else (except members of group
using console with ancient, unpopular login methods such as
over networks as this might be exploitable. (CVE-2001-0797)
This is not enabled by default in this package since this package does not know which users shall be added to group 'console' and thus, would break console.
Brute force attack protection
User accounts are locked after 50 failed login attempts using
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
- Explain locked root account if locked.
Access rights restrictions
Strong user account separation
Read, write and execute access for "others" are removed during package
installation, upgrade or PAM
mkhomedir for all users who have home
/home by running, for example:
chmod o-rwx /home/user
This will be done only once per folder in
/home so users who wish to
relax file permissions are free to do so. This is to protect files in a
home folder that were previously created with lax file permissions prior
to the installation of this package.
SUID / SGID removal and permission hardening
Not enabled by default yet.
A systemd service removes SUID / SGID bits 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.
Access rights relaxations
This is not enabled yet because hidepid is not enabled by default.
pkexec are redirected to
- Enables "
apt-get --error-on=any" which makes apt exit non-zero for transient failures. -
- Enables APT seccomp-BPF sandboxing -
- Deactivates previews in Dolphin.
- Deactivates previews in Nautilus -
- Deactivates thumbnails in Thunar.
- Displays domain names in punycode (
network.IDN_show_punycode) in Thunderbird to prevent IDN homograph attacks (a form of phishing).
- Security and privacy enhancements for gnupg's config file
/etc/skel/.gnupg/gpg.conf. See also:
Some hardening is opt-in as it causes too much breakage to be enabled by default.
An optional systemd service mounts
hidepid=2at boot to prevent users from seeing another user's processes. This is disabled by default because it is incompatible with
pkexec. It can be enabled by executing
systemctl enable proc-hidepid.serviceas root.
A systemd service restricts
/systo the root user. This hides a lot of hardware identifiers from unprivileged users and increases security as
/sysexposes 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 executing
systemctl enable hide-hardware-info.serviceas root.
hardened malloc compatibility for haveged workaround
- Linux Kernel Runtime Guard (LKRG)
- tirdad - TCP ISN CPU Information Leak Protection.
- Kicksecure (TM) - a security-hardened Linux Distribution
- And more.
Happening primarily in forums.
How to install
How to Build deb Package from Source Code
Can be build using standard Debian package build tools such as:
See instructions. (Replace
generic-package with the actual name of this package
- A) easy, OR
- B) including verifying software signatures
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