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
• Send an email to the Security Mailing List

Attribution

Lê Ngọc Khoa reported the vulnerability.

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
• Send an email to the Security Mailing List

Attribution

Lê Ngọc Khoa reported the vulnerability.