Upon receiving each incoming request header data, Envoy will iterate over existing request headers to verify that the total size of the headers stays below a maximum limit. The implementation in versions 1.10.0 through 1.11.1 for HTTP/1.x traffic and all versions of Envoy for HTTP/2 traffic 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.
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Envoy | Envoyproxy | 1.0.0 (including) | 1.0.0 (including) |
| Envoy | Envoyproxy | 1.1.0 (including) | 1.1.0 (including) |
| Envoy | Envoyproxy | 1.2.0 (including) | 1.2.0 (including) |
| Envoy | Envoyproxy | 1.3.0 (including) | 1.3.0 (including) |
| Envoy | Envoyproxy | 1.4.0 (including) | 1.4.0 (including) |
| Envoy | Envoyproxy | 1.5.0 (including) | 1.5.0 (including) |
| Envoy | Envoyproxy | 1.6.0 (including) | 1.6.0 (including) |
| Envoy | Envoyproxy | 1.7.0 (including) | 1.7.0 (including) |
| Envoy | Envoyproxy | 1.7.1 (including) | 1.7.1 (including) |
| Envoy | Envoyproxy | 1.8.0 (including) | 1.8.0 (including) |
| Envoy | Envoyproxy | 1.9.0 (including) | 1.9.0 (including) |
| Envoy | Envoyproxy | 1.9.1 (including) | 1.9.1 (including) |
| Envoy | Envoyproxy | 1.10.0 (including) | 1.10.0 (including) |
| Envoy | Envoyproxy | 1.11.0 (including) | 1.11.0 (including) |
| Envoy | Envoyproxy | 1.11.1 (including) | 1.11.1 (including) |
| Envoy | Envoyproxy | 1.11.2 (including) | 1.11.2 (including) |
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.