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GHSA-9vwc-pc8p-253q

Http4s Ember HTTP/2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS

Source: GitHub Advisory Database (reviewed) High CVE-2026-69203

Packages

EcosystemPackageAffectedFixed in
Maven org.http4s:http4s-ember-core_2.12 < 0.23.35 0.23.35
Maven org.http4s:http4s-ember-core_2.13 < 0.23.35 0.23.35
Maven org.http4s:http4s-ember-core_3 < 0.23.35 0.23.35
Maven org.http4s:http4s-ember-core_2.13 >= 1.0.0-M1, < 1.0.0-M47 1.0.0-M47
Maven org.http4s:http4s-ember-core_3 >= 1.0.0-M1, < 1.0.0-M47 1.0.0-M47

Details

As written in the advisory (Markdown source, shown as plain text).

An ember server with HTTP/2 enabled (`.withHttp2`) does not enforce `SETTINGS_MAX_CONCURRENT_STREAMS` on streams opened by the peer. A single unauthenticated connection can open an unbounded number of concurrent streams, each of which allocates per-stream server state that is never released, exhausting the heap. ## Impact Unauthenticated remote denial of service (memory exhaustion) against any Ember server built `.withHttp2`. This is the resource-exhaustion class of the HTTP/2 "Rapid Reset" family (CVE-2023-44487). The same unchecked allocation path is reachable on the client via server-initiated `PUSH_PROMISE` frames, so a malicious or compromised server can exhaust an ember-client's heap the same way. ## Preconditions - Server: with `.withHttp2` enabled. - Client: makes HTTP/2 requests to malicious or compromised sites. `enablePush` is not enforced. ## Workarounds - Disable HTTP/2 on `EmberServerBuilder` or `EmberClientBuilder` (default) - Client only: avoid HTTP/2 to untrusted servers until patched.

References

External links from the advisory. They lead to third-party sites.