diff --git a/README.md b/README.md index 8c232ae..da9becd 100644 --- a/README.md +++ b/README.md @@ -132,6 +132,9 @@ configuration file and significant hardening is applied to a myriad of component - Disable TCP timestamps as they can allow detecting the system time. +- Disable reuse of `TIME_WAIT` sockets for new outgoing connections as the above + setting disables TCP timestamps. + - Optional - Log packets with impossible source or destination addresses to enable further inspection and analysis. diff --git a/usr/lib/sysctl.d/990-security-misc.conf#security-misc-shared b/usr/lib/sysctl.d/990-security-misc.conf#security-misc-shared index a4914da..c9a3f97 100644 --- a/usr/lib/sysctl.d/990-security-misc.conf#security-misc-shared +++ b/usr/lib/sysctl.d/990-security-misc.conf#security-misc-shared @@ -565,6 +565,16 @@ net.ipv6.conf.*.accept_ra=0 ## net.ipv4.tcp_timestamps=0 +## Disable reuse of TIME_WAIT sockets for new outgoing connections. +## The safety of reusing of TIME_WAIT sockets requires enabling TCP timestamps. +## The kernel uses timestamps to verify a new connection is not a duplicate segment from an older connection. +## Hence TIME-WAIT sockets should wait the full timeout period before being made available again. +## Can lead to port exhaustion on high-traffic networks with numerous short-lived connections. +## +## https://vincent.bernat.ch/en/blog/2014-tcp-time-wait-state-linux +## +net.ipv4.tcp_tw_reuse=0 + ## Enable logging of packets with impossible source or destination addresses. ## Martian and unroutable packets may be used for malicious purposes. ## Recommended to keep a (kernel dmesg) log of these to identify suspicious packets.