CoreDNS is a DNS server that chains plugins. Starting in version 1.2.0 and prior to version 1.12.4, the CoreDNS etcd plugin contains a TTL confusion vulnerability where lease IDs are incorrectly used as TTL values, enabling DNS cache pinning attacks. This effectively creates a DoS condition for DNS resolution of affected services. The `TTL()` function in `plugin/etcd/etcd.go` incorrectly casts etcd lease IDs (64-bit integers) to uint32 and uses them as TTL values. Large lease IDs become very large TTLs when cast to uint32. This enables cache pinning attacks. Version 1.12.4 contains a fix for the issue.