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As of LCOS 10.50 RC3, all DNS queries that pass through the LANCOM DNS forwarder are therefore subjected to a security check. This prevents data tunnels from being transported via DNS messages.
Many Organizations let the DNS protocol pass through their firewall in both directions because their employees have to visit websites in the internet and users or customers have to find the company websites.
The Domain Name System (DNS) is one of the fundamental services of the Internet, and therefore companies usually allow the DNS protocol to pass bidirectionally through their firewall. This is necessary so that, for example, employees can call up external websites and customers or prospective customers are able to find the company's websites.
This offers the usual convenience of using the internet, but also opens up opportunities for potential attackers to infect a network.
One way to attack a network via DNS is the method of DNS tunneling. Here, DNS requests are used A network attack with DNS tunneling takes advantage of this by using DNS queries to implement a command and control channel for malware. Incoming DNS traffic can relay transmits the commands to the malware , while and outgoing DNS traffic can forward data, sensitive information, or responses to Inquiries from malware operators. DNS tunneling transmits sensitive data and information to the attacker. DNS tunnelling can also be used to bypass circumvent regulations in networks, for example by using access point e.g. by leveraging hotspot logins or blocked services.
This works because DNS is a very flexible protocol. There are very few restrictions on the data that a DNS query contains as it is designed to look up domain names for websites. Since almost anything can be a domain name, these fields can be used to convey sensitive information. These queries are designed to target DNS servers controlled by attackers so that they can receive the queries and respond in the appropriate DNS responses.
Due to the fact that the DNS protocol is very adaptable, such actions are usually successful. The requests are designed to be sent to DNS servers that are controlled by the attackers. Thus, the DNS servers are able to receive the requests and transmit data in corresponding DNS responses.
Since numerous DNS tunneling tools are offered for download on the Internet, DNS tunneling attacks can be carried out quite easily. Even inexperienced attackers are thus able to route data past the security devices of a network or, for example, to bypass the login to a (chargeable) WLAN hotspot without having to authenticate the requesting WLAN client.
As of LCOS 10.50 REL, all DNS queries that pass through the LANCOM DNS forwarder are therefore subjected to a security check. This prevents data tunnels from being transported via DNS messagesDNS tunneling attacks are simple to hold out and there are various DNS tunneling toolkits available.This makes it attainable even for inexperienced attackers to use this method to export knowledge past a company' network security solutions (e.g. firewall) or to bypass hotspots, for example, while not having to certify a client.
The check is activated by default, but can be deactivated if required in the configuration in the menu DNS → Filter/Aliases → DNS Tunnel Filter. However, we recommend not deactivating the check.
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