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CVE-2026-87022: Apache Tomcat: WebSocket message smuggling with per-message-deflate

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% 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-130

Description

Improper handling of length parameter inconsistency vulnerability in Apache Tomcat allows WebSocket message smuggling when per-message-deflate is used. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.25, from 10.1.0-M1 through 10.1.59, from 9.0.0.M1 through 9.0.121. The following versions were EOS at the time the CVE was created but are known to be affected: from 8.5.0 through 8.5.100, from 7.0.56 through 7.0.109. Other unsupported versions may also be affected. Users are recommended to upgrade to version 11.0.26, 10.1.60 or 9.1.22, which fix the issue.

Affected products

• Apache Tomcat: from 11.0.0-M1 through 11.0.25; from 10.1.0-M1 through 10.1.59; from 9.0.0.M1 through 9.0.121; from 8.5.0 through 8.5.100; from 7.0.56 through 7.0.109

References

• https://lists.apache.org/thread/ypvlkjqsq0480fnk9jm6h9qllddwlw4w
• http://www.openwall.com/lists/oss-security/2026/09/23/30

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