The push endpoint of a Vaadin application that uses server push reflects the request Origin into the Access-Control-Allow-Origin response header and allows credentials, because Flow configures Atmosphere with DROP_ACCESS_CONTROL_ALLOW_ORIGIN_HEADER set to false and its CorsInterceptor then echoes whatever Origin the request carries. A page on any origin can therefore make a cross origin request to that endpoint with the user's cookies and read the response, although reading anything useful also requires the push identifier of that session. Applications that do not use @Push are not affected, and neither is the WebSocket transport. The behaviour was introduced in January 2015 and is present in every Flow release and in Vaadin Framework from 7.1.0, which is when push was added. Users of affected versions should apply the following mitigation or upgrade. Releases that have fixed this issue include: Product version Vaadin 14.14.0 - 14.14.7 Vaadin 23.6.0 - 23.6.16 Vaadin 24.4.0 - 24.4.25 Vaadin 24.5.0 - 24.5.15 Vaadin 24.6.0 - 24.6.13 Vaadin 24.7.0 - 24.7.16 Vaadin 24.8.0 - 24.8.17 Vaadin 24.9.0 - 24.9.23 Vaadin 24.10.0 - 24.10.11 Vaadin 25.0.0 - 25.0.13 Vaadin 25.1.0 - 25.1.13 Vaadin 25.2.0 - 25.2.10 Vaadin 25.3.0 - 25.3.2 Vaadin Framework 7.1.0 - 7.7.54 Vaadin Framework 8.0.0 - 8.32.1 Mitigation Upgrade to 14.14.8 Upgrade to 23.6.17 Upgrade to 24.4.26 Upgrade to 24.7.17 Upgrade to 24.7.17 Upgrade to 24.7.17 Upgrade to 24.9.24 Upgrade to 24.9.24 Upgrade to 24.10.12 Upgrade to 25.2.11 Upgrade to 25.2.11 Upgrade to 25.2.11 Upgrade to 25.3.3 Upgrade to 7.7.55 Upgrade to 8.32.2 Please note that Vaadin versions 10-13 and 15-22 are no longer supported and you should update either to the latest 14, 23, 24, 25 version. Artifacts under com.vaadin Maven coordinates / Vulnerable versions / Fixed version vaadin / 14.14.0 - 14.14.7 / >=14.14.8 vaadin / 23.6.0 - 23.6.16 / >=23.6.17 vaadin / 24.4.0 - 24.4.25 / >=24.4.26 vaadin / 24.5.0 - 24.5.15 / >=24.7.17 vaadin / 24.6.0 - 24.6.13 / >=24.7.17 vaadin / 24.7.0 - 24.7.16 / >=24.7.17 vaadin / 24.8.0 - 24.8.17 / >=24.9.24 vaadin / 24.9.0 - 24.9.23 / >=24.9.24 vaadin / 24.10.0 - 24.10.11 / >=24.10.12 vaadin / 25.0.0 - 25.0.13 / >=25.2.11 vaadin / 25.1.0 - 25.1.13 / >=25.2.11 vaadin / 25.2.0 - 25.2.10 / >=25.2.11 vaadin / 25.3.0 - 25.3.2 / >=25.3.3 vaadin-core / 14.14.0 - 14.14.7 / >=14.14.8 vaadin-core / 23.6.0 - 23.6.16 / >=23.6.17 vaadin-core / 24.4.0 - 24.4.25 / >=24.4.26 vaadin-core / 24.5.0 - 24.5.15 / >=24.7.17 vaadin-core / 24.6.0 - 24.6.13 / >=24.7.17 vaadin-core / 24.7.0 - 24.7.16 / >=24.7.17 vaadin-core / 24.8.0 - 24.8.17 / >=24.9.24 vaadin-core / 24.9.0 - 24.9.23 / >=24.9.24 vaadin-core / 24.10.0 - 24.10.11 / >=24.10.12 vaadin-core / 25.0.0 - 25.0.13 / >=25.2.11 vaadin-core / 25.1.0 - 25.1.13 / >=25.2.11 vaadin-core / 25.2.0 - 25.2.10 / >=25.2.11 vaadin-core / 25.3.0 - 25.3.2 / >=25.3.3 flow-server / 2.13.0 - 2.13.7 / >=2.13.8 flow-server / 23.6.0 - 23.6.15 / >=23.6.16 flow-server / 24.4.0 - 24.4.18 / >=24.4.19 flow-server / 24.5.0 - 24.5.17 / >=24.7.17 flow-server / 24.6.0 - 24.6.14 / >=24.7.17 flow-server / 24.7.0 - 24.7.15 / >=24.7.16 flow-server / 24.8.0 - 24.8.16 / >=24.9.24 flow-server / 24.9.0 - 24.9.28 / >=24.9.29 flow-server / 24.10.0 - 24.10.14 / >=24.10.15 flow-server / 25.0.0 - 25.0.15 / >=25.2.11 flow-server / 25.1.0 - 25.1.18 / >=25.1.19 flow-server / 25.2.0 - 25.2.12 / >=25.2.13 flow-server / 25.3.0 - 25.3.3 / >=25.3.4 vaadin-server / 7.1.0 - 7.7.54 / >=7.7.55 vaadin-server / 8.0.0 - 8.32.1 / >=8.32.2 vaadin-server-mpr-jakarta / 7.7.36 - 7.7.54 / >=7.7.55 vaadin-server-mpr-jakarta / 8.18.0 - 8.32.1 / >=8.32.2