A vulnerability was found in Envoy, where Envoy 1.11.0 and 1.11.1 will iterate over existing request headers to verify that the total size of the headers stays below a maximum limit. The implementation in affected versions had O(n^2) performance characteristics. A remote attacker may craft a request that stays below the maximum request header size but consists of many thousands of small headers to consume CPU and result in a denial-of-service attack.