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Knowledge document #3423
FRITZ!Box 7582
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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 attempt 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 what are known as 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

  1. Click "Home Network" in the FRITZ!Box user interface.
  2. Click "Network" in the "Home Network" menu.
  3. Click on the "Network Settings" tab.
  4. 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 the field is not displayed, enable the Advanced View first.
  5. 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

  6. Click "Apply" to save the settings.

2 Restarting the FRITZ!Box

  1. Click "System" in the FRITZ!Box user interface.
  2. Click "Backup" in the "System" menu.
  3. Click on the "Restart" tab.
  4. Click the "Restart" button.