---
id: CVE-2026-69209
title: Http4s is a Scala interface for HTTP services
summary: >-
  Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47,
  The shared WebSocket decoder permits unbounded message buffering because
  defragmentation accumulates fragments without a limit and FrameTranscoder
  accepts dec…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-770
vendor: http4s
product: http4s
affected:
  - http4s < 0.23.35
  - 'http4s >= 1.0.0-M1, < 1.0.0-M47'
published: '2026-09-15'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T20:39:16.610'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-69209'
references:
  - url: >-
      https://github.com/http4s/http4s/commit/d578c3c9da6193627d40fa785e612cda7fcd77b3
    label: security-advisories@github.com
  - url: 'https://github.com/http4s/http4s/releases/tag/v0.23.35'
    label: security-advisories@github.com
  - url: 'https://github.com/http4s/http4s/releases/tag/v1.0.0-M47'
    label: security-advisories@github.com
  - url: 'https://github.com/http4s/http4s/security/advisories/GHSA-jrxx-w2m8-5hf5'
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-16T18:25:00.686488Z'
ingestedAt: '2026-09-15T19:42:58.803Z'
epss: 0.0035
epssPercentile: 0.28635
---

## Overview

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, The shared WebSocket decoder permits unbounded message buffering because defragmentation accumulates fragments without a limit and FrameTranscoder accepts declared lengths up to Int.MaxValue. A remote client that completes a WebSocket handshake against an http4s-blaze-server or http4s-ember-server endpoint can exhaust server memory with oversized frames or fragmented messages. The patched decoder applies a configurable 64 MiB default limit to individual frames and defragmented messages through EmberServerBuilder.withMaxWebSocketMessageSize. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.