---
id: CVE-2026-86252
title: >-
  h3 versions before 1.15.9 fail to sanitize carriage return characters in
  EventStream data and comment fields, allowing attackers to inject arbitrary
  SSE events by including unsanitized carriage returns
summary: >-
  h3 versions before 1.15.9 fail to sanitize carriage return characters in
  EventStream data and comment fields, allowing attackers to inject arbitrary
  SSE events by including unsanitized carriage returns. Attackers can inject
  event type di…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'
cwe:
  - CWE-74
  - CWE-93
vendor: h3js
product: h3
affected:
  - h3 < 1.15.9
  - h3 >= 2.0.0-beta.0 < 2.0.1-rc.17
published: '2026-09-06'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:00:18.870'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86252'
references:
  - url: 'https://github.com/h3js/h3/security/advisories/GHSA-4hxc-9384-m385'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/h3-before-1.15.9-sse-event-injection-via-carriage-return
    label: disclosure@vulncheck.com
  - url: 'https://github.com/h3js/h3/security/advisories/GHSA-4hxc-9384-m385'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-86252.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-86252'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2529158'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-86252'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86252'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
epss: 0.00216
epssPercentile: 0.12254
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-08T15:11:57.605320Z'
ingestedAt: '2026-09-07T04:04:50.585Z'
---

## Overview

h3 versions before 1.15.9 fail to sanitize carriage return characters in EventStream data and comment fields, allowing attackers to inject arbitrary SSE events by including unsanitized carriage returns. Attackers can inject event type directives, split single push calls into multiple browser-parsed events, or escape comment fields to inject data, bypassing the prior CVE fix that only addressed newline injection.

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat OpenShift AI (RHOAI) · no fix planned: Red Hat OpenShift AI (RHOAI) · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-86252.json)