CVE-2026-69213

Http4s Ember HTTP/2: unbounded outbound frame queue

Published: Sep 15, 2026Updated: Sep 17, 2026 Sources: CVE List NVDCWE-400

7.5HIGH

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:LAttack Complexity

Low

PR:NPrivileges Required

None

UI:NUser Interaction

None

Scope

S:UScope

Unchanged

Impact

C:NConfidentiality

None

I:NIntegrity

None

A:HAvailability

High

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Weaknesses

CWE-400 CWE-770

Affected Products

http4s

oss-projectaka blaze

http4sLibrary

OSS Libraries / web-framework

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique

Impact

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References

https://github.com/http4s/http4s/security/advisories/GHSA-8f3q-3jmv-7prw

github.com

https://github.com/http4s/http4s/commit/13fe24d6440bde2f1eb70121486cf59c278e6bae

github.com

https://github.com/http4s/http4s/releases/tag/v0.23.35

github.com

and 1 more references View all →

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