Rename linux kernel sysctl hardening.md to linux-kernel-sysctl-hardening.md

2025-12-06 01:02:49 +01:00 · 2019-02-12 21:57:58 -05:00
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+# Linux Kernel `sysctl` Hardening
+
+## Table of Contents
+
+- [Overview](#overview)
+- [Documentation](#documentation)
+- [Disclaimer](#disclaimer)
+- [Keys](#keys)
+  - [Table View](#table-view)
+  - [Flat File View](#flat-file-view)
+
+## Overview
+
+This is a combined list of all the `sysctl` hardening recommendations I could find across multiple sites:
+
+- https://www.cyberciti.biz/faq/linux-kernel-etcsysctl-conf-security-hardening/
+- https://geektnt.com/sysctl-conf-hardening.html
+- https://linoxide.com/how-tos/linux-server-protection/
+- https://cloudpro.zone/index.php/2018/01/30/debian-9-3-server-setup-guide-part-5/
+
+## Documentation
+
+Documentation for **most** of these keys can be found at https://github.com/torvalds/linux/blob/master/Documentation. However, the documentation seems to be for the 2.2 kernel. I cannot find any newer documentation. If you know where I can find newer documentation please submit a [new issue](https://github.com/imthenachoman/How-To-Secure-A-Linux-Server/issues/new).
+
+## Disclaimer
+
+I do not know what most of these settings do. This list is being provided just as reference material. I take no responsibility for anything.
+
+## Keys
+
+### Table View
+
+|`key=value`|Note|[Documentation|
+|--|--|--|
+|`fs.file-max = 65535`||[/sysctl/fs.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/fs.txt)|
+|`fs.protected_hardlinks = 1`||[/sysctl/fs.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/fs.txt)|
+|`fs.protected_symlinks = 1`||[/sysctl/fs.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/fs.txt)|
+|`kernel.core_uses_pid = 1`||[/sysctl/kernel.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt)|
+|`kernel.ctrl-alt-del = 0`||[/sysctl/kernel.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt)|
+|`kernel.kptr_restrict = 2`||[/sysctl/kernel.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt)|
+|`kernel.pid_max = 65536`||[/sysctl/kernel.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt)|
+|`kernel.randomize_va_space = 2`||[/sysctl/kernel.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt)|
+|`kernel.sysrq = 0`||[/sysctl/kernel.txt](https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt)|
+|`net.ipv4.conf.all.accept_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.all.accept_source_route = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.all.log_martians = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.all.rp_filter = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.all.secure_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.all.send_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.default.accept_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.default.accept_source_route = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.default.log_martians = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.default.rp_filter = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.default.secure_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.default.send_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.eth0.accept_redirects = 0`|change `eth0` to your network interface|[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.eth0.accept_source_route = 0`|change `eth0` to your network interface|[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.eth0.log_martians = 0`|change `eth0` to your network interface|[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.eth0.rp_filter = 1`|change `eth0` to your network interface|[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.lo.accept_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.lo.accept_source_route = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.lo.log_martians = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.conf.lo.rp_filter = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.icmp_echo_ignore_all = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.icmp_echo_ignore_broadcasts = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.icmp_ignore_bogus_error_responses = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.ip_forward = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.ip_local_port_range = 2000 65000`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_fin_timeout = 15`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_keepalive_time = 1800`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_max_syn_backlog = 2048`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_max_tw_buckets = 1440000`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_rfc1337 = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_sack = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_syn_retries = 5`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_synack_retries = 2`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_syncookies = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_timestamps = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv4.tcp_window_scaling = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.all.accept_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.all.accept_source_route = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.accept_ra_defrtr = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.accept_ra_pinfo = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.accept_ra_rtr_pref = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.accept_redirects = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.accept_source_route = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.autoconf = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.dad_transmits = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.max_addresses = 1`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+|`net.ipv6.conf.default.router_solicitations = 0`||[/networking/ip-sysctl.txt](https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt)|
+
+### Flat File View
+
+    ###
+    # start from https://github.com/imthenachoman/How-To-Secure-A-Linux-Server/
+    ###
+    
+    ###
+    # start fs
+    # https://github.com/torvalds/linux/blob/master/Documentation/sysctl/fs.txt
+    ###
+
+    fs.file-max = 65535
+    fs.protected_hardlinks = 1
+    fs.protected_symlinks = 1
+
+    ###
+    # end fs
+    ###
+
+    ###
+    # start kernel
+    # https://github.com/torvalds/linux/blob/master/Documentation/sysctl/kernel.txt
+    ###
+
+    kernel.core_uses_pid = 1
+    kernel.ctrl-alt-del = 0
+    kernel.kptr_restrict = 2
+    kernel.pid_max = 65536
+    kernel.randomize_va_space = 2
+    kernel.sysrq = 0
+
+    ###
+    # end kernel
+    ###
+
+    ###
+    # start net
+    # https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt
+    ###
+
+    net.ipv4.conf.all.accept_redirects = 0
+    net.ipv4.conf.all.accept_source_route = 0
+    net.ipv4.conf.all.log_martians = 1
+    net.ipv4.conf.all.rp_filter = 1
+    net.ipv4.conf.all.secure_redirects = 0
+    net.ipv4.conf.all.send_redirects = 0
+    net.ipv4.conf.default.accept_redirects = 0
+    net.ipv4.conf.default.accept_source_route = 0
+    net.ipv4.conf.default.log_martians = 1
+    net.ipv4.conf.default.rp_filter = 1
+    net.ipv4.conf.default.secure_redirects = 0
+    net.ipv4.conf.default.send_redirects = 0
+
+    ##
+    # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    #
+    # remember to change eth0 to your network interface
+    #
+    # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    # !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+    ##
+    net.ipv4.conf.eth0.accept_redirects = 0
+    net.ipv4.conf.eth0.accept_source_route = 0
+    net.ipv4.conf.eth0.log_martians = 0
+    net.ipv4.conf.eth0.rp_filter = 1
+
+    net.ipv4.conf.lo.accept_redirects = 0
+    net.ipv4.conf.lo.accept_source_route = 0
+    net.ipv4.conf.lo.log_martians = 0
+    net.ipv4.conf.lo.rp_filter = 1
+    net.ipv4.icmp_echo_ignore_all = 1
+    net.ipv4.icmp_echo_ignore_broadcasts = 1
+    net.ipv4.icmp_ignore_bogus_error_responses = 1
+    net.ipv4.ip_forward = 0
+    net.ipv4.ip_local_port_range = 2000 65000
+    net.ipv4.tcp_fin_timeout = 15
+    net.ipv4.tcp_keepalive_time = 1800
+    net.ipv4.tcp_max_syn_backlog = 2048
+    net.ipv4.tcp_max_tw_buckets = 1440000
+    net.ipv4.tcp_rfc1337 = 1
+    net.ipv4.tcp_sack = 0
+    net.ipv4.tcp_syn_retries = 5
+    net.ipv4.tcp_synack_retries = 2
+    net.ipv4.tcp_syncookies = 1
+    net.ipv4.tcp_timestamps = 0
+    net.ipv4.tcp_window_scaling = 0
+    net.ipv6.conf.all.accept_redirects = 0
+    net.ipv6.conf.all.accept_source_route = 0
+    net.ipv6.conf.default.accept_ra_defrtr = 0
+    net.ipv6.conf.default.accept_ra_pinfo = 0
+    net.ipv6.conf.default.accept_ra_rtr_pref = 0
+    net.ipv6.conf.default.accept_redirects = 0
+    net.ipv6.conf.default.accept_source_route = 0
+    net.ipv6.conf.default.autoconf = 0
+    net.ipv6.conf.default.dad_transmits = 0
+    net.ipv6.conf.default.max_addresses = 1
+    net.ipv6.conf.default.router_solicitations = 0
+
+    ###
+    # end kernel
+    ###
+    
+    ###
+    # end from https://github.com/imthenachoman/How-To-Secure-A-Linux-Server/
+    ###