high · 7.5

Undertow: undertow-websockets: undertow: pre-auth dos on websocket endpoint with @serverendpoint class with any @onmessage method

CVE-2026-15565 · published 11 Aug 2026

How serious is it

  • Severity: high, CVSS score 7.5 out of 10.
  • No exploit prediction (EPSS) score yet.
  • Not on the CISA list of exploited vulnerabilities.
  • No public exploit in Exploit-DB.

Is your app affected by CVE-2026-15565?

Paste this prompt into Claude Code, Cursor or any AI coding tool: it runs a free Shippable scan of your project and fixes what it finds. Built with Lovable, Bolt or v0? Scan your live app. Or upload your package file.

Who is affected

  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4.25
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7

How to check

  1. Find out whether you run the affected product and which version, then compare it with the versions above.

How to fix

Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
  1. Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
  2. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

A flaw was found in Undertow. A remote attacker can cause Out of Memory on websockets endpoint without authentication on any @ServerEndpoint class that has any @OnMessage method. This allows an attacker to cause Denial of Service attack without authentication and using only a standard WebSocket handshake.

Check your whole app

Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.

References

Merged from CVE List. Last updated 24 Oct 2026. All vulnerabilities · RSS · JSON

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