# CVE-2026-66299 — Apache Tomcat

> As of 2026-07-28, CVE-2026-66299 is a HIGH-severity vulnerability in Apache Tomcat, CVSS v3.1 7.5, EPSS 0.5% (44.4th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-66299, most recently “Apache Tomcat 11.0.25 Fixes 11 Vulnerabilities Including HTTP/2 DoS, Authorization Bypass, and Auth Fail-Open Flaws — NVD Scores 5 of 11 CRITICAL/HIGH Despite Apache's Low/Moderate Ratings”.

**Last updated:** 2026-07-28

## What is CVE-2026-66299?

Uncontrolled Resource Consumption vulnerability in Apache Tomcat's WebSocket chat example. This issue affects Apache Tomcat: from 11.0.0-M20 through 11.0.24, from 10.1.24 through 10.1.57, from 9.0.89 through 9.0.120. Users who have followed the security guidance to remove the examples web application are not affected by this issue. Users are recommended to remove the examples web application or to upgrade to version 11.0.25, 10.1.58 or 9.0.121 (when released), which fix the issue.

The record classifies CVE-2026-66299 under weakness class [CWE-400](https://intel.threadlinqs.com/cwe/CWE-400). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 89 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.5 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **EPSS (FIRST):** 0.5% probability of exploitation in the next 30 days, higher than 44.4% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-28

## Is CVE-2026-66299 being exploited?

It currently carries a trending score of 28 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Apache Software Foundation](https://intel.threadlinqs.com/vendors/apache-software-foundation): Apache Tomcat

## How to fix CVE-2026-66299

No vendor patch reference has been recorded for CVE-2026-66299 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-66299

1 tracked threat in the Threadlinqs corpus references CVE-2026-66299, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Apache Tomcat 11.0.25 Fixes 11 Vulnerabilities Including HTTP/2 DoS, Authorization Bypass, and Auth Fail-Open Flaws — NVD Scores 5 of 11 CRITICAL/HIGH Despite Apache's Low/Moderate Ratings](https://intel.threadlinqs.com/threat/TL-2026-2159) — CRITICAL · 2026-08-26

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [lists.apache.org — vendor advisory](https://lists.apache.org/thread/8owczcc1o8qw1rxmg9gvfk4w2jnh4l5k)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-66299
Full detection coverage and IOCs for threats exploiting CVE-2026-66299 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp