CVE-2020-5415 — concourse
CRITICALCVE-2020-5415 is a critical-severity (CVSS 10) CWE-290 vulnerability in github.com/concourse/concourse. A fix is available for github.com/concourse/concourse — see the affected versions and patch details below.
GitLab 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.
How urgent is this, really
CVE-2020-5415 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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 | 6.4.1go get github.com/concourse/concourse@v6.4.1 |
| 🐹Go | github.com/concourse/concourse | ≥ 1.6.1&&< 6.3.1 | 6.3.1go get github.com/concourse/concourse@v6.3.1 |
| 🐹Go | github.com/concourse/dex | ≥ 6.4.0&&< 6.4.1 | 6.4.1go get github.com/concourse/dex@v6.4.1 |
| 🐹Go | github.com/concourse/dex | ≥ 0.0.0&&< 6.3.1 | 6.3.1go get github.com/concourse/dex@v6.3.1 |
| 🐹Go | github.com/concourse/dex | all versions | 0.0.0-20200730150203-821b48abfd88go get github.com/concourse/dex@v0.0.0-20200730150203-821b48abfd88 |
| 🐹Go | github.com/concourse/concourse | all versions | 0.0.0-20200730151558-b00d1c8d8576go get github.com/concourse/concourse@v0.0.0-20200730151558-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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 CVE-2020-5415 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2020-5415 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2020-5415. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2020-5415 in your dependencies?
O3 Security finds CVE-2020-5415 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.