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Vulnerability · Published Sep 15, 2026 · Assigned by GitHub_M

CVE-2026-69203Http4s Ember HTTP/2: does not enforce SETTINGS_MAX_CONCURRENT_STREAMS

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, An Ember server with HTTP/2 enabled through withHttp2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS for peer-created streams. One unauthenticated connection can open an unbounded number of streams, each retaining per-stream state until heap exhaustion. The same unchecked allocation is reachable in an ember-client through server-initiated PUSH_PROMISE frames because enablePush is not enforced. 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-9vwc-pc8p-253q
Mavenorg.http4s:http4s-ember-core_2.130.23.35GHSA-9vwc-pc8p-253q
Mavenorg.http4s:http4s-ember-core_2.131.0.0-M47GHSA-9vwc-pc8p-253q
Mavenorg.http4s:http4s-ember-core_30.23.35GHSA-9vwc-pc8p-253q
Mavenorg.http4s:http4s-ember-core_31.0.0-M47GHSA-9vwc-pc8p-253q

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