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Vulnerability record · CVE-2021-21411 · published 26 March 2021

CVE-2021-21411: Oauth2 proxy project oauth2 proxy incorrect authorization vulnerability

OOauth2 Proxy Project · Oauth2 Proxy

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.

5.5 CVSS 3.1 Medium EPSS 1.1% · top 36.5% CWE-863 · Incorrect authorization
5.5CVSS 3.1 base score, v2 5.5
1.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
10References
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://docs.gitlab.com/ee/user/group/ Third Party Advisory
https://github.com/oauth2-proxy/oauth2-proxy/commit/0279fa7dff1752f1710707dbd1ffac839de8bbfc PatchThird Party Advisory
https://github.com/oauth2-proxy/oauth2-proxy/releases/tag/v7.1.0 Release NotesThird Party Advisory
https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-652x-m2gr-hppm Third Party Advisory
https://pkg.go.dev/github.com/oauth2-proxy/oauth2-proxy/v7 ProductThird Party Advisory
https://docs.gitlab.com/ee/user/group/ Third Party Advisory
https://github.com/oauth2-proxy/oauth2-proxy/commit/0279fa7dff1752f1710707dbd1ffac839de8bbfc PatchThird Party Advisory
https://github.com/oauth2-proxy/oauth2-proxy/releases/tag/v7.1.0 Release NotesThird Party Advisory
https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-652x-m2gr-hppm Third Party Advisory
https://pkg.go.dev/github.com/oauth2-proxy/oauth2-proxy/v7 ProductThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-21411), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.