GHSA-5fm9-h728-fwpj

trust-dns and trust-dns-server are vulnerable to remotely triggered denial-of-service attacks, consuming both network and CPU resources.

DNS messages with the QR=1 bit set are responded to with a FormErr response.

This allows creating a traffic loop, in which these FormErr responses are sent nonstop between vulnerable servers.

There are two scenarios how this can be exploited: 1) Create a loop between two instances of trust-dns, consuming network resources, or 2) consuming the CPU of a single instance.

With two instances A and B an attacker sends a DNS query with a spoofed source IP address to A.

A replies with a FormErr to B.

Now both servers with ping-pong the message back and forth until by chance the packet is dropped in the network.

Multiple spoofed packets can be sent by the attacker, increasing resource consumption.

A single server can get locked up replying to itself.

Same setup as above, but now A sends the reply to itself.

The packet is sent out as fast as the CPU and network stack manage.

This locks up a CPU core.

Multiple packets from the attacker consume multiple CPU cores.