Coder's OIDC authentication allows email with partially matching domain to register

Vulnerability Description

Coder allows oragnizations to provision remote development environments via Terraform. Prior to versions 2.6.1, 2.7.3, and 2.8.4, a vulnerability in Coder's OIDC authentication could allow an attacker to bypass the `CODER_OIDC_EMAIL_DOMAIN` verification and create an account with an email not in the allowlist. Deployments are only affected if the OIDC provider allows users to create accounts on the provider. During OIDC registration, the user's email was improperly validated against the allowed `CODER_OIDC_EMAIL_DOMAIN`s. This could allow a user with a domain that only partially matched an allowed domain to successfully login or register. An attacker could register a domain name that exploited this vulnerability and register on a Coder instance with a public OIDC provider. Coder instances with OIDC enabled and protected by the `CODER_OIDC_EMAIL_DOMAIN` configuration are affected. Coder instances using a private OIDC provider are not affected, as arbitrary users cannot register through a private OIDC provider without first having an account on the provider. Public OIDC providers are impacted. GitHub authentication and external authentication are not impacted. This vulnerability is remedied in versions 2.8.4, 2.7.3, and 2.6.1 All versions prior to these patches are affected by the vulnerability.*It is recommended that customers upgrade their deployments as soon as possible if they are utilizing OIDC authentication with the `CODER_OIDC_EMAIL_DOMAIN` setting.

References

• https://github.com/coder/coder/security/advisories/GHSA-7cc2-r658-7xpf
• https://github.com/coder/coder/commit/1171ce7add017481d28441575024209ac160ecb0
• https://github.com/coder/coder/commit/2ba84911f8b02605e5958d5e4a2fe3979ec50b31
• https://github.com/coder/coder/commit/2d37eb42e7db656e343fe1f36de5ab1a1a62f4fb
• https://github.com/coder/coder/commit/4439a920e454a82565e445e4376c669e3b89591c