Overview
This is the version of an Apereo CAS project vulnerability disclosure, describing an issue in CAS that when it’s acting as an OpenID Connect identity provider. If you are not using CAS as an OpenID Connect Provider, there is nothing to do here. Keep calm and carry on.
For additional details on how security issues, patches and announcements are handled, please read the Apereo CAS project vulnerability disclosure process.
Affected Deployments
The security issue described here, per the CAS maintenance policy, affects the Apereo CAS server for the following versions:
- 6.4.x
- 6.5.x
If your CAS version is not listed above AND is still part of an active maintenance cycle per the CAS maintenance policy, then best effort (analysis or confirmation from reporters/testers) indicates that the version is not affected by this issue. That said, please note that per the project’s Apache2 license, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.. For additional information, please see the project license.
If you or your institution is a member of the Apereo foundation with an active support subscription supporting the CAS project, please contact the CAS subs working group to learn more about this security vulnerability report.
Severity
The underlying issue is related to revoking previously-issued OAuth/OIDC access tokens when an expired or invalid OAuth code is submitted to the CAS server in exchange for an access token. In this scenario, CAS will correctly reject the invalid code but begins to query the ticket registry to find all other access tokens previously issued for the invalid code to revoke those. This could potentially lead to a DDOS attack on any CAS system acting as an OIDC server by providing fake OAuth codes on the /token endpoint.
Timeline
The issue was originally reported on March 2nd, 2022 and upon confirmation, CAS releases were patched on March 5th, 2022 and released on March 6th, 2022.
Patching
Patch releases are available to address CAS deployments. Upgrades to the next patch version for each release should be a drop-in replacement.
Procedure
6.4.x
Modify your CAS overlay to point to the version 6.4.6.1.
6.5.x
Modify your CAS overlay to point to the version 6.5.1.
Support
Apereo CAS is Apache v2 open source software under the sponsorship of the Apereo Foundation, supported by community volunteers and enthusiasts. Support options may be found here.
If you or your institution is a member of the Apereo foundation with an active subscription supporting the CAS project, please contact the CAS subs working group to learn more about this security vulnerability report.
Resources
On behalf of the CAS Application Security working group,