OpenTelemetry Collector module AWS Firehose Receiver Authentication Bypass Vulnerability
SummaryOpenTelemetry Collector module [`awsfirehosereceiver`](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/awsfirehosereceiver) allows unauthenticated remote requests, even when configured to require a key.OpenTelemetry Collector can be configured to receive CloudWatch metrics via an AWS Firehose Stream. [Firehose sets the header](https://docs.aws.amazon.com/firehose/latest/dev/httpdeliveryrequestresponse.html) `X-Amz-Firehose-Access-Key` with an arbitrary configured string. The OpenTelemetry Collector awsfirehosereceiver can optionally be configured to require this key on incoming requests. However, when this is configured it **still accepts incoming requests with no key**.ImpactOnly OpenTelemetry Collector users configured with the “[alpha](https://github.com/open-telemetry/opentelemetry-collector#alpha)” `awsfirehosereceiver` module are affected. This module was [added](https://github.com/open-telemetry/opentelemetry-collector-releases/pull/74) in version v0.49.0 of the [“Contrib” distribution](https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib) (or may be included in custom builds).There is a risk of unauthorized users writing metrics. Carefully crafted metrics could hide other malicious activity. There is no risk of exfiltrating data. It’s likely these endpoints will be exposed to the public internet, as Firehose [does not support private HTTP endpoints](https://docs.aws.amazon.com/firehose/latest/dev/controlling-access.html#using-iam-http).FixA fix was introduced in https://github.com/open-telemetry/opentelemetry-collector-contrib/pull/34847 and released with v0.108.0 (https://github.com/open-telemetry/opentelemetry-collector-releases/releases/tag/v0.108.0).DetailsPoCWhen simulating Firehose requests against vulnerable versions of the Collector, we can see “UNAUTHORIZED METRICS” printed to the console via the debug exporter.
(Note this script doesn’t run on some older still-vulnerable versions that do not have the “debug” exporter.)PatchThe [`if` statement](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/v0.107.0/receiver/awsfirehosereceiver/receiver.go#L235) makes the access key header optional, rather than the configuration optional.This has been patched in #34847 to separately handle the case where access_key is not configured, and use a default-deny style: