CVE-2026-77791 Apache Tomcat: DoS via busy wait during WebSocket close
Attackers can cause a denial of service in Apache Tomcat by triggering a busy wait during WebSocket close messages.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-77791?
CVE-2026-77791 is a high-severity denial of service vulnerability in Apache Tomcat, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Uncontrolled Resource Consumption vulnerability in Apache Tomcat during sending of WebSocket close message enabled a DoS attack.
This issue affects Apache Tomcat: from 11.0.0-M5 through 11.0.25, from 10.1.8 through 10.1.59, from 9.0.74 through 9.0.121.
The following versions were EOL at the time the CVE was created but are known to be affected: from 8.5.88 through 8.5.100. Other unsupported versions may also be affected.
Users are recommended to upgrade to version 11.0.26, 10.1.60 or 9.0.122, which fix the issue.
Weakness: CWE-400
Which versions are affected by CVE-2026-77791?
1 open source package ship an affected version, including tomcat.
| Package | Affected | Fixed in |
|---|---|---|
tomcat Bitnami | From 8.5.88 | 9.0.45, 9.0.122, 10.1.60, 11.0.26 |
How do I fix CVE-2026-77791?
Upgrade tomcat to a fixed version for your release line: 9.0.45, 9.0.122, 10.1.60 or 11.0.26.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77791 being exploited?
There is no known exploitation of CVE-2026-77791 in the wild and no public exploit code.
Sources
Also known as BIT-tomcat-2026-77791, DEBIAN-CVE-2026-77791, GHSA-9cg7-2q68-g3mq, MINI-8mc6-r2g9-4w7f, MINI-qxf3-jq24-6gv4, MINI-rx28-m2q3-cx5h and 1 more.