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CVE-2021-21411

MediumCVSS 5.5 / 10
Published Mar 26, 2021·Last modified Apr 2, 2026
Affected Components(0)

No affected components available

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.

Risk Scores
Base Score
5.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.

Threat Intelligence
5.1

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.99%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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