GHSA-88hf-wf7h-7w4m OpenTelemetry's Zipkin remote endpoint cache could grow without bounds and increase memory pressure

• NuGet OpenTelemetry.Exporter.Zipkin: < 1.15.3 → fixed in 1.15.3

Summary The Zipkin exporter remote endpoint cache accepted unbounded key growth derived from span attributes. In high-cardinality scenarios, this could increase process memory usage over time and degrade availability. Details • Introduce a bounded, thread-safe LRU cache for remote endpoints. • Enforce fixed maximum size to prevent unbounded growth. Impact • A process using Zipkin export for client/producer spans could experience avoidable memory growth under sustained unique remote endpoint values. Resources #7081