SonicOS 7.1 DNS Guide

DNS Rebinding Attack Prevention

DNS rebinding is a DNS-based attack on code embedded in web pages. Normally requests from code embedded in web pages (JavaScript, Java, and Flash) are bound to the website they are originating from (see Same Origin Policy). A DNS rebinding attack can be used to improve the ability of JavaScript-based malware to penetrate private networks and subvert the browser's same-origin policy.

DNS rebinding attackers register a domain that is delegated to a DNS server they control. The server is configured to respond with a very short Time to Live (TTL) parameter, which prevents the result from being cached. The first response contains the IP address of the server hosting the malicious code. Any subsequent requests contain IP addresses from private (RFC 1918) network, presumably behind a firewall, being target of the attacker. Because both are fully valid DNS responses, they authorize the sandbox script to access hosts in a private network. By iterating addresses in these short-term but still valid DNS replies, the script is able to scan the network and perform other malicious activities.

To configure DNS rebinding attack prevention

  1. Navigate to NETWORK | DNS > Settings.
  2. Select Enable DNS Rebinding Attack Prevention under DNS Rebinding Attack Prevention section. This option is not selected by default. The two options become available.
  3. From the Action drop-down menu, select an action to perform when a DNS rebinding attack is detected:
    • Log Attack
    • Log Attack & Return a Query Refused Reply
    • Log Attack & Drop DNS Reply
  4. From the Allowed Domains drop-down menu, select an allowed domain FQDN Address Object or FQDN Address Object Group containing allowed domain-names (such as *.SonicWall.com) for which locally connected/routed subnets should be considered legal responses.

    You can also create new FQDN address objects or FQDN address object groups by selecting Create new FQDN Address Object Group… or Create new FQDN Address Object….

  5. Click Accept.

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