CVE-2021-21411
MEDIUMCVE-2021-21411 is a medium-severity (CVSS 5.5) CWE-863 vulnerability in github.com/oauth2-proxy/oauth2-proxy/v7. O3 Security confirms whether CVE-2021-21411 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
OAuth2-Proxy's `--gitlab-group` GitLab Group Authorization config flag stopped working in v7.0.0
Blast Radius
github.com/oauth2-proxy/oauth2-proxy/v7Real-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
OAuth2-Proxy is an open source reverse proxy that provides authentication with Google, Github or other providers. The --gitlab-group flag for group-based authorization in the GitLab provider stopped working in the v7.0.0 release. Regardless of the flag settings, authorization wasn't restricted. Additionally, any authenticated users had whichever groups were set in --gitlab-group added to the new X-Forwarded-Groups header to the upstream application. While adding GitLab project based authorization support in #630, a bug was introduced where the user session's groups field was populated with the --gitlab-group config entries instead of pulling the individual user's group membership from the GitLab Userinfo endpoint. When the session groups where compared against the allowed groups for authorization, they matched improperly (since both lists were populated with the same data) so authorization was allowed. This impacts GitLab Provider users who relies on group membership for authorization restrictions. Any authenticated users in your GitLab environment can access your applications regardless of --gitlab-group membership restrictions. This is patched in v7.1.0. There is no workaround for the Group membership bug. But --gitlab-project can be set to use Project membership as the authorization checks instead of groups; it is not broken.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/oauth2-proxy/oauth2-proxy/v7 | all versions | 7.1.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/oauth2-proxy/oauth2-proxy/v7. 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/oauth2-proxy/oauth2-proxy/v7 to 7.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21411 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 CVE-2021-21411 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 CVE-2021-21411. 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-2021-21411 in your dependencies?
O3 detects CVE-2021-21411 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.