OAuth2: PKCE can be fully circumvented
Vulnerability Description
authentik is an open-source identity provider. When initialising a oauth2 flow with a `code_challenge` and `code_method` (thus requesting PKCE), the single sign-on provider (authentik) must check if there is a matching and existing `code_verifier` during the token step. Prior to versions 2023.10.4 and 2023.8.5, authentik checks if the contents of `code_verifier` is matching only when it is provided. When it is left out completely, authentik simply accepts the token request with out it; even when the flow was started with a `code_challenge`. authentik 2023.8.5 and 2023.10.4 fix this issue.
Impact Analysis
Refer to official advisory for detailed impact metrics.
Remediation
Ensure systems are updated to the latest vendor-supplied patch levels.
Am I Vulnerable?
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Credits & Attribution
No credits recorded in the NVD database.
References
- https://github.com/goauthentik/authentik/security/advisories/GHSA-fm34-v8xq-f2c3
- https://github.com/goauthentik/authentik/pull/7666
- https://github.com/goauthentik/authentik/pull/7668
- https://github.com/goauthentik/authentik/pull/7669
- https://github.com/goauthentik/authentik/commit/3af77ab3821fe9c7df8055ba5eade3d1ecea03a6
- https://github.com/goauthentik/authentik/commit/6b9afed21f7c39f171a4a445654cfe415bba37d5
- https://github.com/goauthentik/authentik/commit/b88e39411c12e3f9e04125a7887f12354f760a14
- https://github.com/goauthentik/authentik/blob/dd4e9030b4e667d3720be2feda24c08972602274/authentik/providers/oauth2/views/token.py#L225
- https://github.com/goauthentik/authentik/releases/tag/version%2F2023.10.4
- https://github.com/goauthentik/authentik/releases/tag/version%2F2023.8.5
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