CVE-2026-69213: HTTP4S

High severity, CVSS 7.5. EPSS: 0.6% chance of exploitation in the next 30 days.

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, Ember HTTP/2 serializes outbound frames through one unbounded queue consumed by writeLoop. When the peer stops reading, an unauthenticated HTTP/2 client can continue sending PING, SETTINGS, or DATA frames that cause Ember to enqueue acknowledgments or WINDOW_UPDATE frames faster than the writer drains them, exhausting heap memory on a server built with withHttp2. The shared behavior also affects an ember-client connected to a hostile HTTP/2 server, and the patch replaces the unbounded path with bounded, backpressured outbound queues. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Affected products

• HTTP4S HTTP4S: before 0.23.35 (fixed in 0.23.35); from 1.0.0-M1, before 1.0.0-M47 (fixed in 1.0.0-M47)

Published 2026-09-15. Last modified 2026-09-17.