CVE-2026-66299: Uncontrolled Resource Consumption vulnerability in Apache Tomcat's WebSocket chat example. This issue affects

This month

MEDIUM 5.3REMOTEWATCHLISTUPGRADE

CVE-2026-66299 is a medium-severity flaw (CVSS 5.3) affecting tomcat. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 55%)
CISA exploited list	No
Weakness	CWE-400
Published	2026-07-28
Last modified	2026-10-24

Publisher (CNA): Apache Software Foundation · Vendor: apache

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-28 15:17 UTCPublished CVE record published
2026-10-24 13:10 UTCUpdated Record last modified

apache tomcat UPGRADE

Affected: >= 9.0.89 and < 9.0.121 · >= 10.1.24 and < 10.1.58 · >= 11.0.1 and < 11.0.25 · 11.0.0 milestone20 · 11.0.0 milestone21 · 11.0.0 milestone22 · 11.0.0 milestone23 · 11.0.0 milestone24

Fixed in: 9.0.121, 10.1.58, 11.0.25

Safe to downgrade to: a release before 9.0.89

1. Check installed version

apt-cache policy tomcat || rpm -q tomcat || tomcat --version

2. UPGRADE to 9.0.121 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade tomcat

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade tomcat

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 9.0.89 (Debian / Ubuntu)

apt-cache madison tomcat sudo apt install tomcat=<VERSION_BEFORE_9.0.89> sudo apt-mark hold tomcat

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list tomcat sudo dnf downgrade tomcat-<VERSION_BEFORE_9.0.89> sudo dnf versionlock add tomcat

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora ELN · ntpd-rs · FIXED · 1.7.2-3.eln159 · FEDORA-2026-57e4a99310 · source

sudo dnf upgrade --advisory=FEDORA-2026-57e4a99310

Fedora 46 · moby-engine · FIXED · 29.9.2-2.fc46 · FEDORA-2026-4856be87b3 · source

sudo dnf upgrade --advisory=FEDORA-2026-4856be87b3

Debian 12 · tomcat10 · NO FIX YET

Debian 13 · tomcat10 · NO FIX YET

Debian 13 · tomcat11 · NO FIX YET

Debian 12 · tomcat9 · FIXED · 9.0.70-2

sudo apt update && sudo apt install --only-upgrade tomcat9 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' tomcat9)" ge "9.0.70-2" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · tomcat · NO FIX YET

RHEL 10 · tomcat9 · NO FIX YET

RHEL 6 · tomcat6 · NOT AFFECTED

RHEL 7 · tomcat · NOT AFFECTED

RHEL 8 · pki-deps:10.6/pki-servlet-engine · NOT AFFECTED

Advisories and coverage

Official advisories

Amazon Linux 2 ALAS: ALAS2TOMCAT9-2026-028 (important): tomcat 2026-08-31

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-66299?

tomcat: upgrade to 9.0.121, 10.1.58, 11.0.25. Exact commands for each OS are on this page.

Is CVE-2026-66299 being exploited?

CVE-2026-66299 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-66299 affect?

CVE-2026-66299 affects tomcat. Severity is medium (CVSS 5.3). 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 followe

How urgent is CVE-2026-66299?

Priority 40/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

Apache Tomcat vulnerabilities

References

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