Action captions in Vaadin accept HTML by default but were not sanitized, potentially allowing Cross-site Scripting (XSS) if caption content is derived from user input. In Vaadin Framework 7 and 8, the Action class is a general-purpose class that may be used by multiple components. The fixed versions sanitize captions by default and provide an API to explicitly enable HTML content mode for backwards compatibility. In Vaadin 23 and newer, the Action class is only used by the Spreadsheet component. The fixed versions sanitize HTML using Jsoup with a relaxed safelist. Vaadin 14 is not affected as Spreadsheet component was not supported. Users of affected versions should apply the following mitigation or upgrade. Releases that have fixed this issue include: Product version Vaadin 7.0.0 - 7.7.49 Vaadin 8.0.0 - 8.29.1 Vaadin 23.1.0 - 23.6.5 Vaadin 24.0.0 - 24.8.13 Vaadin 24.9.0 - 24.9.6 Mitigation Upgrade to 7.7.50 Upgrade to 8.30.0 Upgrade to 23.6.6 Upgrade to 24.8.14 or 24.9.7 Upgrade to 25.0.0 or newer Artifacts     Maven coordinatesVulnerable versionsFixed versioncom.vaadin:vaadin-server 7.0.0 - 7.7.49 ≥7.7.50 com.vaadin:vaadin-server 8.0.0 - 8.29.1 ≥8.30.0 com.vaadin:vaadin 23.1.0 - 23.6.5 ≥23.6.6 com.vaadin:vaadin24.0.0 - 24.8.13 ≥24.8.14 com.vaadin:vaadin24.9.0 - 24.9.6 ≥24.9.7 com.vaadin:vaadin-spreadsheet-flow 23.1.0 - 23.6.5 ≥23.6.6 com.vaadin:vaadin-spreadsheet-flow 24.0.0 - 24.8.13 ≥24.8.14 com.vaadin:vaadin-spreadsheet-flow 24.9.0 - 24.9.6 ≥24.9.7

jsoup is a Java HTML parser, built for HTML editing, cleaning, scraping, and cross-site scripting (XSS) safety. jsoup may incorrectly sanitize HTML including `javascript:` URL expressions, which could allow XSS attacks when a reader subsequently clicks that link. If the non-default `SafeList.preserveRelativeLinks` option is enabled, HTML including `javascript:` URLs that have been crafted with control characters will not be sanitized. If the site that this HTML is published on does not set a Content Security Policy, an XSS attack is then possible. This issue is patched in jsoup 1.15.3. Users should upgrade to this version. Additionally, as the unsanitized input may have been persisted, old content should be cleaned again using the updated version. To remediate this issue without immediately upgrading: - disable `SafeList.preserveRelativeLinks`, which will rewrite input URLs as absolute URLs - ensure an appropriate [Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) is defined. (This should be used regardless of upgrading, as a defence-in-depth best practice.)