---
id: "CVE-2026-101572"
kind: "vulnerability"
aliases: ["CVE-2026-101572"]
title: "Helidon HTTP/2 client flaw lets unauthenticated attackers crash or hang services"
severity: "high"
cvss: 7.5
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "helidon-webclient-http2", "fixed": [], "affected": ">= 4.0.0, <= 4.5.5; 27.0.0", "ecosystem": "maven"}]
ecosystems: []
tags: ["denial-of-service", "helidon", "http2", "java", "oracle-fusion-middleware", "package", "webclient"]
not_affected_if: ["helidon-3.x", "no-http2-webclient", "unaffected-version"]
published_at: "2026-10-20T22:18:10+00:00"
first_seen_at: "2026-10-23T21:57:22+00:00"
updated_at: "2026-10-25T03:26:04+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-101572", "first_seen_at": "2026-10-23T21:57:22+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-25T03:26:04+00:00"}]
---

# Helidon HTTP/2 client flaw lets unauthenticated attackers crash or hang services

Helidon's HTTP/2 web client component has a flaw that an unauthenticated attacker on the network can trigger over HTTP/2. Successful exploitation hangs or repeatedly crashes the Helidon application, a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- maven:helidon-webclient-http2 affected >= 4.0.0, <= 4.5.5; 27.0.0 fixed ?

## How to check

Look for io.helidon.webclient:helidon-webclient-http2 (directly or through helidon-webclient) at 4.0.0-4.5.5 or 27.0.0: run mvn dependency:tree or gradle dependencies and grep helidon-webclient-http2. Only apps that use Helidon's HTTP/2 WebClient are in scope.

## Fix

Likely upgrade to Helidon 4.5.6 (4.x line) or 27.0.1 (27.x line); not confirmed against Oracle's Helidon risk matrix row. Check the CPU October 2026 advisory (Fusion Middleware, Helidon) before relying on it.

## Timeline

- 2026-10-23T21:57:22+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-101572
- 2026-10-25T03:26:04+00:00 analyst — Affected range 4.0.0-4.5.5 and 27.0.0 confirmed via CVE record (Oracle CNA). Oracle CPU Oct 2026 matrix section for Helidon not read (page truncated), so fixed version is unconfirmed; 4.5.6 (20 Oct) and 27.0.1 exist and likely fix it. No exploitation or PoC found. Not marked verified. Related Helidon HTTP/2 DoS CVEs: CVE-2026-83276 (webclient), CVE-2026-83280 (webserver), fixed in earlier range <=4.5.4.

## Documents

- [advisory] Oracle Critical Patch Update Advisory - October 2026 https://www.oracle.com/security-alerts/cpuoct2026.html
- [describes] CVE Record: CVE-2026-101572 https://www.cve.org/CVERecord?id=CVE-2026-101572
- [fix] Helidon releases (4.5.6, 20 Oct 2026) https://github.com/helidon-io/helidon/releases

## From the sources

Vulnerability in the Helidon product of Oracle Fusion Middleware (component: helidon-webclient-http2).  Supported versions that are affected are 4.0.0-4.5.5 and 27.0.0. Easily exploitable vulnerability allows unauthenticated attacker with network access via HTTP/2 to compromise Helidon.  Successful attacks of this vulnerability can result in unauthorized ability to cause a hang or frequently repeatable crash (complete DOS) of Helidon. CVSS 3.1 Base Score 7.5 (Availability impacts).  CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

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