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Disable reuse of TIME_WAIT sockets #335

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Merged
adrelanos merged 1 commit into from
Dec 3, 2025
Merged

Disable reuse of TIME_WAIT sockets #335

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3 changes: 3 additions & 0 deletions README.md
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Expand Up @@ -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.

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10 changes: 10 additions & 0 deletions usr/lib/sysctl.d/990-security-misc.conf#security-misc-shared
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Expand Up @@ -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.
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