Vulnerability in trust-dns and trust-dns-server (#1703)

An attacker can form packet loops between vulnerable instances leading
to a denial-of-service for both network and CPU resources.

crates/trust-dns-server/RUSTSEC-0000-0000.md

@@ -0,0 +1,31 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "trust-dns-server"
+date = "2023-06-01"
+url = "https://github.com/bluejekyll/trust-dns/pull/1952"
+categories = ["denial-of-service"]
+keywords = ["packet loop"]
+
+[versions]
+patched = ["^0.22.1", ">=0.23.0-alpha.3"]
+```
+
+# Remote Attackers can cause Denial-of-Service (packet loops) with crafted DNS packets
+
+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.