Pages of a website hosted in Plesk fail to load: Size of a request header field exceeds server limit

Dmitry Bystrov

1 year ago

Symptoms

Website pages fail to open with the following error message in a web-browser:

Bad request
Your browser sent a request that this server could not understand.
Size of a request header field exceeds server limit.

Size of a request header field has exceeded the server limit defined in Apache configuration. The default Apache header size is 8 KB.

For Apache on CentOS/RHEL-based distributions (global)

Connect to the Plesk server via SSH.
Create a backup of the Apache configuration file:

# cp -a /etc/httpd/conf/httpd.conf /root/httpd.conf_`date +%F`
Open the file in a text editor. In this example, we are using the vi editor:

# vi /etc/httpd/conf/httpd.conf
Add the following line and specify your value (16000 is an example):

LimitRequestFieldSize 16000
Save the changes and close the file.
Restart the Apache service to apply the changes:

# service httpd restart

Note: In case the value of 16000 (16KB) is not enough, increase it to the greater value, for example, 32000 (32KB).

For Apache on Debian/Ubuntu-based distributions (global)

Connect to the Plesk server via SSH.
Create a backup of the Apache configuration file:

# cp /etc/apache2/apache2.conf /etc/apache2/apache2.conf_`date +%F`
Open the file in a text editor. In this example, we are using the vi editor:

# vi /etc/apache2/apache2.conf
Add the following line and specify your value (16000 is an example):

LimitRequestFieldSize 16000
Save the changes and close the file.
Restart the Apache service to apply the changes:

# service apache2 restart

Note: In case the value of 16000 (16KB) is not enough, increase it to the greater value, for example, 32000 (32KB).

For nginx-only hosting (single domain)

If the website is using nginx-only hosting, apply the following steps:

Log in to Plesk.
Go to Domains > example.com > Hosting & DNS > Apache & nginx Settings.
Add the following line to Additional nginx directives then hit Apply.

large_client_header_buffers 4 16k;

Note: Edit 16k to match whatever request buffer size you need keeping in mind 8k is default, and the larger the buffer size the greater the impact from a DDOS attack.

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