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Knowledge document #3423
FRITZ!Box 4020
This support document is available for the following products:
FRITZ!Box reports "400 Bad Request" when accessed with own domain name or CNAME
The error message "400 Bad Request ERR_INVALID_REQ" is displayed when you try to use your own domain name or CNAME to access the FRITZ!Box user interface.
Cause
- For security reasons, the FRITZ!Box blocks attempts from unfamiliar domain names and via CNAME to access its user interface. This is a security function of the FRITZ!Box to protect against so-called DNS rebinding attacks.
Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.
1 Configuring exceptions for DNS rebind protection
- Click "Home Network" in the FRITZ!Box user interface.
- Click "Network" in the "Home Network" menu.
- Click on the "Network Settings" tab.
- In the "Domain name exceptions" field in the section "DNS Rebind Protection", enter the complete domain name (with subdomain, if applicable) or CNAME for which DNS rebind protection should not apply.
- If you want to configure exceptions for several domain names, enter each domain name on a new line.
Example:
my-domain.com
abcd1234.myfritz.net - Click "Apply" to save the settings.
2 Restarting the FRITZ!Box
- Click "System" in the FRITZ!Box user interface.
- Click "Backup" in the "System" menu.
- Click on the "Restart" tab.
- Click the "Restart" button.