GHSA-627p-rr78-99rj
HIGHGitLab auth uses full name instead of username as user ID, allowing impersonation
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/concourse/concourse🐹github.com/concourse/concourse🐹github.com/concourse/dex🐹github.com/concourse/dex🐹github.com/concourse/dex🐹github.com/concourse/concourse🐹github.com/concourse/concourseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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 [email protected].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/concourse/concourse | ≥ 6.4.0&&< 6.4.1 | 6.4.1 |
| 🐹Go | github.com/concourse/concourse | ≥ 1.6.1&&< 6.3.1 | 6.3.1 |
| 🐹Go | github.com/concourse/dex | ≥ 6.4.0&&< 6.4.1 | 6.4.1 |
| 🐹Go | github.com/concourse/dex | ≥ 0.0.0&&< 6.3.1 | 6.3.1 |
| 🐹Go | github.com/concourse/dex | all versions | 0.0.0-20200730150203-821b48abfd88 |
| 🐹Go | github.com/concourse/concourse | all versions | 0.0.0-20200730151558-b00d1c8d8576 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/concourse/concourse. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/concourse/concourse to 6.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-627p-rr78-99rj is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-627p-rr78-99rj is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-627p-rr78-99rj. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-627p-rr78-99rj in your dependencies?
O3 detects GHSA-627p-rr78-99rj across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.