security-misc/usr/lib/sysctl.d/990-security-misc.conf

## Copyright (C) 2019 - 2024 ENCRYPTED SUPPORT LP <adrelanos@whonix.org>
## See the file COPYING for copying conditions.

## NOTE:
## This file has a weird file name so /usr/lib/sysctl.d/99-protect-links.conf
## is parsed first and /usr/lib/sysctl.d/990-security-misc.conf is parsed
## afterwards. See also:
## https://github.com/Kicksecure/security-misc/pull/135

## Restricts the kernel log to root only.
kernel.dmesg_restrict=1

## Disables coredumps. This setting may be overwritten by systemd so this may not be useful.
## security-misc also disables coredumps in other ways.
kernel.core_pattern=|/bin/false

## Does not set coredump name to 'core' which is default. Defense in depth.
kernel.core_uses_pid=1

## Prevent setuid processes from creating coredumps.
fs.suid_dumpable=0

## Don't allow writes to files that we don't own
## in world writable sticky directories, unless
## they are owned by the owner of the directory.
fs.protected_fifos=2
fs.protected_regular=2

## Only allow symlinks to be followed when outside of
## a world-writable sticky directory, or when the owner
## of the symlink and follower match, or when the directory
## owner matches the symlink's owner.
##
## Prevent hardlinks from being created by users that do not
## have read/write access to the source file.
##
## These prevent many TOCTOU races.
fs.protected_symlinks=1
fs.protected_hardlinks=1

## Hides kernel addresses in various files in /proc.
## Kernel addresses can be very useful in certain exploits.
##
## https://kernsec.org/wiki/index.php/Bug_Classes/Kernel_pointer_leak
kernel.kptr_restrict=2

## Improves ASLR effectiveness for mmap.
## Both explicit sysctl are made redundant due to automation
## https://forums.whonix.org/t/automate-mmap-randomisation-to-fix-ppc64el/16514
## Do NOT enable either - displaying only for clarity
##
#vm.mmap_rnd_bits=32
#vm.mmap_rnd_compat_bits=16

## Restricts the use of ptrace to root. This might break some programs running under WINE.
## A workaround for WINE would be to give the wineserver and wine-preloader ptrace capabilities. This can be done by running:
##
## sudo apt-get install libcap2-bin
## sudo setcap cap_sys_ptrace=eip /usr/bin/wineserver
## sudo setcap cap_sys_ptrace=eip /usr/bin/wine-preloader
kernel.yama.ptrace_scope=2

## Randomize the addresses for mmap base, heap, stack, and VDSO pages
kernel.randomize_va_space=2

## Hardens the BPF JIT compiler and restricts it to root.
kernel.unprivileged_bpf_disabled=1
net.core.bpf_jit_harden=2

## Disable asynchronous I/O for all processes.
## Valid only for linux kernel version >= 6.6.
## Command is retained here for future-proofing and completeness.
## https://forums.whonix.org/t/io-uring-security-vulnerabilties/16890/6
kernel.io_uring_disabled=2

#### meta start
#### project Kicksecure
#### category networking and security
#### description
## TCP/IP stack hardening

## A martian packet is a one with a source address which is blatantly wrong
## Recommended to keep a log of these to identify these suspicious packets
## Good for troubleshooting and diagnostics but not necessary by default.
## Caused issue:
## https://github.com/Kicksecure/security-misc/issues/214
#net.ipv4.conf.all.log_martians=1
#net.ipv4.conf.default.log_martians=1

## Protects against time-wait assassination.
## It drops RST packets for sockets in the time-wait state.
net.ipv4.tcp_rfc1337=1

## Disables ICMP redirect acceptance.
net.ipv4.conf.all.accept_redirects=0
net.ipv4.conf.default.accept_redirects=0
net.ipv4.conf.all.secure_redirects=0
net.ipv4.conf.default.secure_redirects=0
net.ipv6.conf.all.accept_redirects=0
net.ipv6.conf.default.accept_redirects=0

## Disables ICMP redirect sending.
net.ipv4.conf.all.send_redirects=0
net.ipv4.conf.default.send_redirects=0

## Ignores ICMP requests.
net.ipv4.icmp_echo_ignore_all=1
net.ipv6.icmp.echo_ignore_all=1

## Ignores bogus ICMP error responses
net.ipv4.icmp_ignore_bogus_error_responses=1

## Enables TCP syncookies.
net.ipv4.tcp_syncookies=1

## Disable source routing.
net.ipv4.conf.all.accept_source_route=0
net.ipv4.conf.default.accept_source_route=0
net.ipv6.conf.all.accept_source_route=0
net.ipv6.conf.default.accept_source_route=0

## Enable reverse path filtering to prevent IP spoofing and
## mitigate vulnerabilities such as CVE-2019-14899.
## https://forums.whonix.org/t/enable-reverse-path-filtering/8594
net.ipv4.conf.default.rp_filter=1
net.ipv4.conf.all.rp_filter=1

#### meta end


## Previously disabled SACK, DSACK, and FACK.
## https://forums.whonix.org/t/disabling-tcp-sack-dsack-fack/8109
#net.ipv4.tcp_sack=0
#net.ipv4.tcp_dsack=0
#net.ipv4.tcp_fack=0


#### meta start
#### project Kicksecure
#### category networking and security
#### description
## disable IPv4 TCP Timestamps

net.ipv4.tcp_timestamps=0

#### meta end


## Disable SysRq key
kernel.sysrq=0

## Restrict loading TTY line disciplines to CAP_SYS_MODULE to prevent
## unprivileged attackers from loading vulnerable line disciplines
## with the TIOCSETD ioctl which has been used in exploits before
## such as https://a13xp0p0v.github.io/2017/03/24/CVE-2017-2636.html
##
## https://lkml.org/lkml/2019/4/15/890
dev.tty.ldisc_autoload=0

## Restrict the userfaultfd() syscall to root as it can make heap sprays
## easier.
##
## https://duasynt.com/blog/linux-kernel-heap-spray
vm.unprivileged_userfaultfd=0

## Let the kernel only swap if it is absolutely necessary.
## Better not be set to zero:
## - https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Performance_Tuning_Guide/s-memory-tunables.html
## - https://en.wikipedia.org/wiki/Swappiness
vm.swappiness=1

## Disallow kernel profiling by users without CAP_SYS_ADMIN
## https://www.kernel.org/doc/Documentation/sysctl/kernel.txt
kernel.perf_event_paranoid=3

## Do not accept router advertisements
net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.default.accept_ra=0