CVE-2026-76183

Apache Tomcat: Bypass of security constraints for WebSocket endpoints

Summary

Incorrect interpretation of WebSocket endpoint paths can bypass Tomcat declarative security constraints.

The issue affects Apache Tomcat 9.0.0.M1 through 9.0.121 in the 9.0 branch and is fixed in Tomcat 9.0.122. The bundled version, 9.0.120, falls within this version range; exploitability depends on the conditions described below.

The Critical classification reflects the CISA assessment in the CVE record: 9.8 (CVSS 3.1). Apache rates this issue Important. The upstream severity is distinct from PageSeeder exposure.

For technical details, see the Apache Tomcat security advisory .

PageSeeder impact assessment

Assessment

PageSeeder is not affected by CVE-2026-76183 in the reviewed standard configuration because the required configuration or application usage was not found.

Required conditions for exploitation: A WebSocket endpoint protected by Tomcat declarative security constraints that can be bypassed through alternate request path interpretation.

Relevant PageSeeder configuration: PageSeeder uses application permission checks in URIEndpoint and RecentLogsEndpoint. No applicable declarative WebSocket security constraints were found.

Evidence from source and configuration review:

• URIEndpoint checks login and edit permission before subscribing a connection to URI editing events.
• RecentLogsEndpoint checks login and system administrator permission before subscribing a connection to recent logs.
• No security-constraint declarations or ServletSecurity annotations implementing the vulnerable protection model were found. This finding concerns this CVE only; it is not a general proof of WebSocket security.

This assessment is limited to the repository revision and configuration reviewed on 11 November 2026. It does not independently verify the historical PageSeeder version range in the model advisory. Customised connectors, deployment descriptors, extensions and additional web applications may change exposure.

The PageSeeder installer source was also reviewed at commit a08323b (Windows, Linux EL7, EL8 and EL9). Installer review supports the standard configuration assessment; it does not establish the configuration of every deployed server. Linux RPM packaging marks server.xml CONFIG | NOREPLACE, so existing administrator changes can survive upgrades.

Recommended action

Administrators who add declarative constraints to WebSocket endpoints, or host other applications relying on them, should upgrade to Tomcat 9.0.122 or later, preferably 9.0.123 or later. Verify endpoint authorization independently.

For installations matching the reviewed unaffected configuration, no CVE-specific emergency change is required. Confirm the installed configuration before relying on this conclusion. Use a supported PageSeeder distribution containing an updated Tomcat where available; this advisory does not announce a PageSeeder release date or confirm that such a distribution has shipped.

Dependency maintenance recommendation: update the bundled Tomcat to 9.0.123 or a later supported release, which also incorporates fixes for the other Critical CVEs covered in this advisory set.

References

• CVE-2026-76183 record and CISA severity assessment 
• Apache Tomcat security advisory 
• Apache Tomcat 9 security advisories 
• Apache Tomcat 9 changelog