CVE-2026-34151

XWiki Platform is a generic wiki platform. Prior to 17.10.5 and 18.2.0, the /skin/ action in com.xpn.xwiki.web.SkinAction can resolve double-encoded parent-directory segments outside the intended skin or web-application resource prefix when Jetty 12 or later decodes the request path. The affected lookup is replaced with Environment.getResourceAsStream(String, String), which constrains a resource to its expected prefix. An unauthenticated remote attacker can use the vulnerable behavior to read arbitrary resources permitted to the Jetty process, including WEB-INF/xwiki.cfg and, depending on deployment depth and operating-system permissions, host files. Tomcat and Jetty versions before 12 do not appear affected. This issue is fixed in versions 17.10.5 and 18.2.0.

XWiki Platform is a generic wiki platform. Prior to 17.10.5 and 18.2.0, the /skin/ action in com.xpn.xwiki.web.SkinAction can resolve double-encoded parent-directory segments outside the intended skin or web-application resource prefix when Jetty 12 or later decodes the request path. The affected lookup is replaced with Environment.getResourceAsStream(String, String), which constrains a resource to its expected prefix. An unauthenticated remote attacker can use the vulnerable behavior to read arbitrary resources permitted to the Jetty process, including WEB-INF/xwiki.cfg and, depending on deployment depth and operating-system permissions, host files. Tomcat and Jetty versions before 12 do not appear affected. This issue is fixed in versions 17.10.5 and 18.2.0.

### Impact With Jetty 12+ a user can craft a URL to access any resource the Jetty instance is allowed to access. For example `http://[host]/xwiki/bin/skin/..%252f/..%252f..%252f..%252f..%252f..%252f..%252f..%252fetc/passwd` allows downloading the content of the /etc/passwd file, provided Jetty is allowed to read it, and if your XWiki webapp is located exactly 5 levels below `/` (like `/var/lib/jetty/webapps/xwiki`, which is the case in the docker image, for example). Another example which does not go out of the XWiki webapp, but it's still a vulnerability (since users should not be allowed to access Hibernate or XWiki configuration files) is `http://[host]/xwiki/bin/skin/..%252f/..%252fWEB-INF/xwiki.cfg`. ### Patches This vulnerability has been patched in XWiki 17.10.5 and 18.2.0. ### Workarounds A possible workaround is to use a different application server, like Jetty < 12 (in the case of XWiki < 17) or Tomcat, which don't seem to be impacted. ### Resources * https://jira.xwiki.org/browse/XWIKI-24075 * https://jira.xwiki.org/browse/XCOMMONS-3594 ### For more information If there are any questions or comments about this advisory: * Open an issue in [Jira XWiki.org](https://jira.xwiki.org/) * Send an email to the [Security Mailing List](mailto:[email protected]) ### Attribution Lê Ngọc Khoa reported the vulnerability.

### Impact With Jetty 12+ a user can craft a URL to access any resource the Jetty instance is allowed to access. For example `http://[host]/xwiki/bin/skin/..%252f/..%252f..%252f..%252f..%252f..%252f..%252f..%252fetc/passwd` allows downloading the content of the /etc/passwd file, provided Jetty is allowed to read it, and if your XWiki webapp is located exactly 5 levels below `/` (like `/var/lib/jetty/webapps/xwiki`, which is the case in the docker image, for example). Another example which does not go out of the XWiki webapp, but it's still a vulnerability (since users should not be allowed to access Hibernate or XWiki configuration files) is `http://[host]/xwiki/bin/skin/..%252f/..%252fWEB-INF/xwiki.cfg`. ### Patches This vulnerability has been patched in XWiki 17.10.5 and 18.2.0. ### Workarounds A possible workaround is to use a different application server, like Jetty < 12 (in the case of XWiki < 17) or Tomcat, which don't seem to be impacted. ### Resources * https://jira.xwiki.org/browse/XWIKI-24075 * https://jira.xwiki.org/browse/XCOMMONS-3594 ### For more information If there are any questions or comments about this advisory: * Open an issue in [Jira XWiki.org](https://jira.xwiki.org/) * Send an email to the [Security Mailing List](mailto:[email protected]) ### Attribution Lê Ngọc Khoa reported the vulnerability.