CAS Vulnerability Disclosure


Overview

This is the public version of an Apereo CAS project vulnerability disclosure describing an issue in CAS where an adversary may be able to bypass certain administrative endpoints, in spite of CAS access rule in place. The following administrative endpoints are exposed and vulnerable to this attack:

  • /configserver/
  • /cas/status/metrics

Affected Deployments

The attack vector specifically applies to all deployments of CAS 5.0.x deployments. If you have deployed any version of CAS 5.0.x, you MUST take action to upgrade. If you have deployed any other versions of CAS, disregard this announcement.

Severity

This is a serious issue where successfully exercising this vulnerability allows the adversary gain insight into the running CAS software, collect stats and metrics and potentially observe the collection of configured CAS settings in configuration files.

Patching

Patch releases are available to address CAS 5.0.x deployments. Upgrades to the next patch version for each release should be a drop-in replacement. The patch simply ensures that the exposed endpoints honor the CAS access rules, and otherwise block attempts. When you have applied the patch, please double check all endpoints and ensure access is appropriately controlled.

Timeline

The issue was originally reported to the CAS application security team on February 20, 2017. Upon confirmation, CAS was patched on February 22, 2017 and released. The original release announcement is available here.

Procedure

Update Version

Modify your CAS overlay to point to version 5.0.3.1. A snippet of a pom.xml for a CAS overlay follows:

<dependencies>
    <dependency>
        <groupId>org.jasig.cas</groupId>
        <artifactId>cas-server-webapp</artifactId>
        <version>${cas.version}</version>
        <type>war</type>
        <scope>runtime</scope>
    </dependency>
</dependencies>

<properties>
    <cas.version>5.0.3.1</cas.version>
</properties>

Double check your cas.properties file for the following setting:

# cas.adminPagesSecurity.ip=the-authorized-ip-pattern

Adjust Overlay

If your CAS build has overlaid the src/main/resources/bootstrap.properties file, make sure the following line is corrected there:

spring.cloud.config.server.prefix=/status/configserver

Alternatives

If you are unable to apply the patch, it’s then best to ensure the outlined endpoints are blocked completely via load balancers, proxies, firewalls, etc.

Support

If you have questions on the details this vulnerability and how it might be reproduced, please contact security@apereo.org or cas-appsec-public@apereo.org.

Resources

Related Posts

CAS 6.1.0 RC3 Feature Release

...in which I present an overview of CAS 6.1.0 RC3 release.

Apereo CAS 6.1.x - Credential Caching & Proxy AuthN

Learn how you may configure Apereo CAS to capture and cache the credential's password and the proxy-granting ticket in proxy authentication scenarios, pass them along to applications as regular attributes/claims. We will also be reviewing a handful of attribute release strategies that specifically affect authentication attributes, conveying metadata about the authentication event itself.

Apereo CAS 6.1.x - Attribute Repositories w/ Person Directory

An overview of CAS attribute repositories and strategies on how to fetch attributes from a variety of sources in addition to the authentication source, merge and combine attributes from said sources to ultimately release them to applications with a fair bit of caching.

Apereo CAS 6.1.x - Building CAS Feature Modules

An overview of how various CAS features modules today can be changed and tested from the perspective of a CAS contributor working on the codebase itself to handle a feature request, bug fix, etc.

CAS 6.1.0 RC2 Feature Release

...in which I present an overview of CAS 6.1.0 RC2 release.

Apereo CAS - Riffing on Attribute Release Policies

Learn how to release the kraken of attributes to CAS clients, relying parties and service providers using a variety of attribute release policies and authentication protocols, sampled and collected here to fun and profit.

Apereo CAS - Delegated Authentication to SAML2 Identity Providers

Learn how your Apereo CAS deployment may be configured to delegate authentication to an external SAML2 identity provider.

Apereo CAS - Custom Login Fields w/ Dynamic Bindings

Learn how to extend the Spring Webflow model to add custom fields to the CAS login form and the authentication process and take advantage of the additional user-provided data in customized authentication handlers.

Apereo CAS as an OAuth2 Authorization Server

Learn how to configure CAS as an OAuth2 Authorization Server and configure Spring Boot client app to work with it

Apereo CAS - SAML2 Identity Provider Integration w/ Gitlab (also staring HAProxy and LDAP)

Learn how Apereo CAS may act as a SAML2 identity provider for Gitlab and run everything locally on a workstation with Docker and Java.