ClassLoaderTheme and ClasspathThemeResourceProviderFactory allows reading any file available as a resource to the classloader. By sending requests for theme resources with a relative path from an external HTTP client, the client will receive the content of random files if available.
References
- https://nvd.nist.gov/vuln/detail/CVE-2021-3856
- https://github.com/keycloak/keycloak/pull/8588
- https://github.com/keycloak/keycloak/commit/73f0474008e1bebd0733e62a22aceda9e5de6743
- https://access.redhat.com/security/cve/CVE-2021-3856
- https://bugzilla.redhat.com/show_bug.cgi?id=2010164
- https://issues.redhat.com/browse/KEYCLOAK-19422
- https://github.com/advisories/GHSA-3w4v-rvc4-2xpw