http4s has HTTP/2 Denial of Service with Ember Backend

Summary http4s 0.23.x and 1.0 servers running ember with http2 enabled are vulnerable to a denial of service attack using a HPACK bomb vulnerability recently disclosed as affecting other http2 servers. Impact Denial of Service: - Affects any http4s server running the ember backend with HTTP/2...

CVE-2026-54556

http4s (Scala HTTP library) versions prior to 0.23.35 and 1.0.0-M47 are vulnerable to an out-of-memory denial of service when using the Ember backend with HTTP/2 enabled. The root cause is a HPACK bomb : the Hpack wrapper concatenates HEADERS and CONTINUATION frame fragments into a single decoded...

EUVD-2026-66558

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, an unauthenticated HTTP/2 peer can cause an out-of-memory denial of service in the Ember backend with HTTP/2 enabled. The Hpack wrapper in ember-core/shared/src/main/scala/org/http4s/ember/core/h2/Hpack.scala...