CVE-2021-3856: Path Traversal
First published: Mon Oct 04 2021(Updated: )
<a href="https://issues.redhat.com/browse/KEYCLOAK-19422">https://issues.redhat.com/browse/KEYCLOAK-19422</a> <a href="https://github.com/keycloak/keycloak/blob/master/services/src/main/java/org/keycloak/theme/ClasspathThemeResourceProviderFactory.java">https://github.com/keycloak/keycloak/blob/master/services/src/main/java/org/keycloak/theme/ClasspathThemeResourceProviderFactory.java</a> The ThemeResource resource exposes an endpoint for fetching theme resources: @GET @Path("/{version}/{themeType}/{themeName}/{path:.*}") public Response getResource(@PathParam("version") String version, @PathParam("themeType") String themType, @PathParam("themeName") String themeName, @PathParam("path") String path) { ... } The classbased resource loaders are implemented as: public InputStream getResourceAsStream(String path) { return classLoader.getResourceAsStream(resourceRoot + path); } This has no checks for the path parameter, allowing relative traversals like ../. 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. I practice this exposes any files packages within the deployed module, including other resources available as a classloader resource. Disallowing double dots in the path component is probably the easiest fix
Credit: secalert@redhat.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Redhat Keycloak | <15.1.0 |
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Reference Links
- https://issues.redhat.com/browse/KEYCLOAK-19422
- https://github.com/keycloak/keycloak/blob/master/services/src/main/java/org/keycloak/theme/ClasspathThemeResourceProviderFactory.java
- https://access.redhat.com/support/policy/updates/jboss_notes
- https://access.redhat.com/solutions/5941551
- https://bugzilla.redhat.com/show_bug.cgi?id=2010164
- https://access.redhat.com/security/cve/CVE-2021-3856
- https://github.com/keycloak/keycloak/commit/73f0474008e1bebd0733e62a22aceda9e5de6743
- https://github.com/keycloak/keycloak/pull/8588
Frequently Asked Questions
What is CVE-2021-3856?
CVE-2021-3856 is a vulnerability in ClassLoaderTheme and ClasspathThemeResourceProviderFactory that allows reading any file available as a resource to the classloader.
What is the severity of CVE-2021-3856?
CVE-2021-3856 has a severity of medium with a CVSS score of 4.3.
What software is affected by CVE-2021-3856?
Redhat Keycloak versions up to 15.1.0 are affected by CVE-2021-3856.
How can an attacker exploit CVE-2021-3856?
An attacker can exploit CVE-2021-3856 by sending requests for theme resources with a relative path from an external HTTP client, allowing them to receive the content of random files if available.
Is there a fix for CVE-2021-3856?
Yes, upgrading to a version of Redhat Keycloak that is not affected, such as version 15.1.1 or higher, will fix CVE-2021-3856.
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