The Apollo Router Core is a configurable, high-performance graph router written in Rust to run a federated supergraph that uses Apollo Federation 2. A vulnerability in Apollo Router's usage of Apollo Compiler allowed queries with deeply nested and reused named fragments to be prohibitively expensive to validate. This could lead to excessive resource consumption and denial of service. Apollo Router's usage of Apollo Compiler has been updated so that validation logic processes each named fragment only once, preventing redundant traversal. This has been remediated in apollo-router versions 1.61.2 and 2.1.1.