From 23d8a2718eea1a301cbe0cb1572d09d98cfb6dca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miroslav=20=C5=A0ediv=C3=BD?= <sedivy.miro@gmail.com>
Date: Wed, 28 Oct 2026 17:05:56 +0100
Subject: [PATCH] oauth: ignore email when provider reports
 email_verified=false.

An unverified email could match admin_emails/user_emails on providers that
let users set their own email. Only an explicit false is rejected; providers
that omit the claim are still trusted. Document the behavior.

Reported-by: Zachariah Mithani <zachariah@aplosai.com> (AploSec)
---
 server/internal/member/oauth/service.go      |  6 ++++++
 server/internal/member/oauth/utils.go        | 15 +++++++++++++
 server/internal/member/oauth/utils_test.go   | 22 ++++++++++++++++++++
 webpage/docs/configuration/authentication.md |  4 ++++
 4 files changed, 47 insertions(+)
 create mode 100644 server/internal/member/oauth/utils_test.go

diff --git a/server/internal/member/oauth/service.go b/server/internal/member/oauth/service.go
index 8910125f..6169f9ce 100644
--- a/server/internal/member/oauth/service.go
+++ b/server/internal/member/oauth/service.go
@@ -168,6 +168,12 @@ func (service *Service) Complete(ctx context.Context, stateToken, code string) (
 		email = claim(idClaims, "email")
 	}
 
+	// Providers that omit email_verified are trusted; only an explicit false is rejected.
+	if email != "" && (claimFalse(claims, "email_verified") || claimFalse(idClaims, "email_verified")) {
+		log.Warn().Msg("OAuth provider reported the email as unverified; ignoring it for admin_emails/user_emails")
+		email = ""
+	}
+
 	if email == "" && (len(config.AdminEmails) > 0 || len(config.UserEmails) > 0) {
 		log.Warn().Msg("OAuth admin_emails/user_emails are configured but the provider did not return an 'email' claim; request the 'email' scope")
 	}
diff --git a/server/internal/member/oauth/utils.go b/server/internal/member/oauth/utils.go
index b60809cf..24b170c2 100644
--- a/server/internal/member/oauth/utils.go
+++ b/server/internal/member/oauth/utils.go
@@ -70,6 +70,21 @@ func boolClaim(claims map[string]any, field string) bool {
 	return false
 }
 
+// claimFalse reports whether the claim is present and explicitly false.
+func claimFalse(claims map[string]any, field string) bool {
+	value, ok := claims[field]
+	if !ok {
+		return false
+	}
+	switch value := value.(type) {
+	case bool:
+		return !value
+	case string:
+		return strings.EqualFold(value, "false")
+	}
+	return false
+}
+
 func administrator(email string, isAdmin bool, emails []string) bool {
 	if isAdmin {
 		return true
diff --git a/server/internal/member/oauth/utils_test.go b/server/internal/member/oauth/utils_test.go
new file mode 100644
index 00000000..95c4a85d
--- /dev/null
+++ b/server/internal/member/oauth/utils_test.go
@@ -0,0 +1,22 @@
+package oauth
+
+import "testing"
+
+func TestClaimFalse(t *testing.T) {
+	cases := []struct {
+		name   string
+		claims map[string]any
+		want   bool
+	}{
+		{"absent", map[string]any{}, false},
+		{"true", map[string]any{"email_verified": true}, false},
+		{"false", map[string]any{"email_verified": false}, true},
+		{"string true", map[string]any{"email_verified": "true"}, false},
+		{"string false", map[string]any{"email_verified": "False"}, true},
+	}
+	for _, tc := range cases {
+		if got := claimFalse(tc.claims, "email_verified"); got != tc.want {
+			t.Errorf("%s: got %v, want %v", tc.name, got, tc.want)
+		}
+	}
+}
diff --git a/webpage/docs/configuration/authentication.md b/webpage/docs/configuration/authentication.md
index f5922245..8c588d3c 100644
--- a/webpage/docs/configuration/authentication.md
+++ b/webpage/docs/configuration/authentication.md
@@ -234,6 +234,10 @@ The sign-in endpoint is `GET /api/oauth/login`; the callback endpoint is `GET /a
 `admin_emails` and `user_emails` are matched against the `email` claim. Most providers only include that claim if the `email` scope is requested, so `scopes` must include `"email"` (in addition to `"openid"`) or the claim will be empty and these lists will never match.
 :::
 
+:::warning
+If the provider returns `email_verified: false`, Neko ignores the email, so it cannot match `admin_emails` or `user_emails`. If the claim is missing, the email is trusted, because many providers (including generic OAuth2 providers such as GitHub) do not return it at all. In that case `admin_emails` and `user_emails` rely on the identity provider having verified the address. If users can register or edit their email without verification on a provider that does not send `email_verified`, anyone could claim an address listed in `admin_emails` and obtain an administrator session. Require email verification at the provider or do not use these lists.
+:::
+
 For OAuth sessions, `GET /api/whoami` includes `extra_data`: the merged userinfo and ID-token claims, with userinfo values taking precedence. It is returned only to the authenticated session owner and is intended for profile-field troubleshooting. Do not place secrets in provider profile claims.
 
 For non-OIDC providers, set `authorization_url`, `token_url`, `userinfo_url`, and optionally `redirect_url` directly. For GitHub, for example, use `read:user` as a scope and set `subject_field: id`, `username_field: login`, and `avatar_field: avatar_url`.