EUVD-2026-43723
GHSA-8hm4-r66f-29wr
Severity by source
AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:N
Any backend role (secretary, provider) can exploit this over the network with no victim interaction; AC:L because provider_id is a guessable integer; PR:L reflects the lowest backend role required.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
3DescriptionCVE.org
Easy!Appointments is a self hosted appointment scheduler. In versions prior to 1.6.0, Google::oauth at application/controllers/Google.php:278 stores its URL-supplied provider_id in the session, and oauth_callback saves the issued Google OAuth token against that row without checking the caller owns the provider. Any logged-in backend user (admin, provider, or secretary) rebinds a peer provider's Google sync to a Google account they control. The peer's appointments then sync into the attacker's calendar with each customer's name and email attached as attendee data. Version 1.6.0 patches the issue.
AnalysisAI
OAuth provider rebinding in Easy!Appointments prior to version 1.6.0 allows any authenticated backend user - including low-privilege secretary and provider roles - to silently hijack a peer provider's Google Calendar integration by supplying an arbitrary provider_id to the OAuth initiation endpoint. The attacker completes a legitimate Google OAuth flow with their own Google account, which the application then binds to the victim provider's database row without verifying ownership. From that point forward, every appointment on the victim's schedule syncs to the attacker's Google Calendar, leaking customer names and email addresses as attendee data. No public exploit has been identified at time of analysis, and the vulnerability is not listed in the CISA KEV catalog.
Technical ContextAI
Easy!Appointments is a PHP-based self-hosted scheduling application (CPE: cpe:2.3:a:alextselegidis:easyappointments:*:*:*:*:*:*:*:*). The flaw resides in application/controllers/Google.php. The Google::oauth method accepts a provider_id from the URL query string and stores it unsanitized in the PHP session. When the Google OAuth callback (oauth_callback) is triggered, the application retrieves this session-stored provider_id and writes the newly issued Google OAuth token to that provider's database record - without confirming that the requesting user's session identity matches the target provider or that the user holds administrative privileges. This is a textbook CWE-639 (Authorization Bypass Through User-Controlled Key) pattern: the provider_id functions as an insecure direct object reference (IDOR) key that the caller fully controls. The fix in commit 4b2d245d2cd2058dc76e05f6eb65b26699268471 adds an ownership and permission gate - enforcing either PRIV_USERS edit rights (admin) or a match between the session user_id and the target oauth_provider_id - and clears the session variable after use to prevent replay.
RemediationAI
Upgrade to Easy!Appointments version 1.6.0, which is confirmed as the patched release per the project description and the CHANGELOG entry in commit 4b2d245d2cd2058dc76e05f6eb65b26699268471. The fix enforces that only administrators (with PRIV_USERS edit rights) or the provider whose own ID matches the OAuth initiation request may complete the Google OAuth binding flow; all others receive HTTP 403. The patch also nullifies the session-stored oauth_provider_id after use, preventing replay. If immediate upgrade is not possible, restrict backend account creation to fully trusted users, disable Google Calendar sync for the installation until patching is completed, and audit the google_sync and google_token columns in the providers table for unexpected OAuth bindings. The commit and advisory are at https://github.com/alextselegidis/easyappointments/commit/4b2d245d2cd2058dc76e05f6eb65b26699268471 and https://github.com/alextselegidis/easyappointments/security/advisories/GHSA-8hm4-r66f-29wr.
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