CVE-2026-86350

Apache Tomcat: HTTP/2 request header mix-up

Summary

A regression in HTTP/2 request processing can mix request headers between requests, potentially compromising request confidentiality or integrity.

The issue affects Apache Tomcat 9.0.118 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: 9.1 (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-2026-86350 in its standard installer-generated and Docker configurations because Tomcat HTTP/2 is not enabled. Customised installations that enable HTTP/2 require a separate assessment.

Required conditions for exploitation: HTTP/2 enabled on a Tomcat connector. The issue is a regression in the fix for CVE-2026-41293.

Relevant PageSeeder configuration: Windows and Linux installers generate HTTP/1.1 connectors and do not add Http2Protocol or UpgradeProtocol. Docker also enables HTTP/1.1 only. Standard installer-generated configurations therefore do not expose the affected HTTP/2 processing.

Evidence from source and configuration review:

• The bundled Tomcat version contains the affected HTTP/2 implementation.
• The supplied Docker connectors use HTTP/1.1 and do not configure Http2Protocol.
• Installer review confirms HTTP/1.1 connectors in windows/script/UpgradeFunctions.nsh (AddTomcatConnectors), linux/rpm/el7/includes/configure.sh and linux/rpm/el8/includes/bin/setup.sh (update_connector). No Http2Protocol or UpgradeProtocol is added.
• Linux EL8 and EL9 packages share the EL8 connector configuration through linux/build.gradle. Their supplied server.xml enables plaintext HTTP/1.1 on port 8282.

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

Check installed tomcat/conf/server.xml for org.apache.coyote.http2.Http2Protocol. Installations using Tomcat HTTP/2 should upgrade to Tomcat 9.0.122 or later, preferably 9.0.123 or later to address the other advisories. Disabling Tomcat HTTP/2 removes this prerequisite.

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-2026-86350 record and CISA severity assessment 
• Apache Tomcat security advisory 
• Apache Tomcat 9 security advisories 
• Apache Tomcat 9 changelog