CVE-2020-5415: Concourse's GitLab auth allows impersonation
Impact
Installations which use the GitLab auth connector are vulnerable to identity spoofing by way of configuring a GitLab account with the same full name as another GitLab user who is granted access to a Concourse team by having their full name listed under users in the team configuration or given to the --gitlab-user flag.
See the GitLab auth docs for details.
Concourse installations which do not configure the GitLab auth connector are not affected.
Patches
Concourse v6.3.1 and v6.4.1 were both released with a fix on August 4th, 2020.
Both versions change the GitLab connector to use the username, rather than the full name. This was always the intent, and the previous behavior was originally reported as a bug (concourse/dex#7) prior to being reported as a security issue.
Any Concourse teams which configure GitLab users will have to switch each user from their full name to their username upon upgrading to these versions.
Workarounds
GitLab groups do not have this vulnerability, so GitLab users may be moved into groups which are then configured in the Concourse team.
References
concourse/dex#12: PR with the fix
For more information
If you have any questions or comments about this advisory, you may reach us privately at concourseteam+security@gmail.com.
Other sources
Concourse, versions prior to 6.3.1 and 6.4.1, in installations which use the GitLab auth connector, is vulnerable to identity spoofing by way of configuring a GitLab account with the same full name as another user who is granted access to a Concourse team. GitLab groups do not have this vulnerability, so GitLab users may be moved into groups which are then configured in the Concourse team.
Affected Software
Remediation
Event History
Frequently Asked Questions
What is CVE-2020-5415?
CVE-2020-5415 is a vulnerability in Concourse versions prior to 6.3.1 and 6.4.1 that affects installations using the GitLab auth connector and allows identity spoofing.
How does CVE-2020-5415 affect Concourse installations?
CVE-2020-5415 affects Concourse installations that use the GitLab auth connector and have versions prior to 6.3.1 or 6.4.1.
What is the severity of CVE-2020-5415?
CVE-2020-5415 has a severity rating of critical with a severity value of 10.
How can I fix CVE-2020-5415?
To fix CVE-2020-5415, update Concourse to version 6.3.1 or 6.4.1 if you are using the GitLab auth connector.
Where can I find more information about CVE-2020-5415?
You can find more information about CVE-2020-5415 in the official GitHub advisory (https://github.com/concourse/concourse/security/advisories/GHSA-627p-rr78-99rj) and the VMware security advisory (https://tanzu.vmware.com/security/cve-2020-5415).