Servers – Ensure TCP SYN Cookies is Enabled

This check ensures that TCP SYN cookies are enabled on the system.

Enabling SYN cookies helps protect against SYN flood attacks and ensures reliable network availability.

Check Details

Resource: Server
Check: Ensure TCP SYN cookies are enabled
Risk: Disabled SYN cookies can make the system vulnerable to SYN flood attacks, leading to denial of service and disruption of legitimate connections.

Set the active kernel parameters by running the following commands:

sysctl -w net.ipv4.tcp_syncookies=1
sysctl -w net.ipv4.route.flush=1

Make the configuration persistent across reboots.
For standard Linux distributions, create or edit the sysctl configuration file:
```
sudo nano /etc/sysctl.d/60-netipv4_sysctl.conf
```
Add the following line to the file:
```
net.ipv4.tcp_syncookies = 1
```
Alternatively, you can update the main sysctl configuration file:
```
sudo nano /etc/sysctl.conf
```
Add the following line:
```
net.ipv4.tcp_syncookies = 1
```
Save the file and exit.
Apply the changes:
```
sudo sysctl -p
```
Re-run audit commands to confirm the configuration is applied successfully.

Updated on 06 March, 2026