Log in Start free

Vulnerability · Published Sep 15, 2026 · Assigned by GitHub_M

CVE-2026-69213Http4s Ember HTTP/2: unbounded outbound frame queue

High 7.5

In plain English

A high-severity uncontrolled resource consumption in http4s from http4s. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.6%top 49.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Mavenorg.http4s:http4s-ember-core_2.120.23.35GHSA-8f3q-3jmv-7prw
Mavenorg.http4s:http4s-ember-core_2.130.23.35GHSA-8f3q-3jmv-7prw
Mavenorg.http4s:http4s-ember-core_2.131.0.0-M47GHSA-8f3q-3jmv-7prw
Mavenorg.http4s:http4s-ember-core_30.23.35GHSA-8f3q-3jmv-7prw
Mavenorg.http4s:http4s-ember-core_31.0.0-M47GHSA-8f3q-3jmv-7prw

Affected products (as reported)

VendorProductVersions
http4s http4s < 0.23.35>= 1.0.0-M1, < 1.0.0-M47

Weakness: CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References