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CVE-2026-77791: Apache Tomcat: DoS via busy wait during WebSocket close

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-23 · updated 2026-09-23
• Weakness: CWE-400

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.

Affected products

• 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; from 8.5.88 through 8.5.100

References

• https://lists.apache.org/thread/mb1pjjooqytrl6hbvbt3rw1lqwlon4cz
• http://www.openwall.com/lists/oss-security/2026/09/23/24

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