Executive brief
Wallos is an open-source personal subscription tracker that helps users manage and monitor their recurring payments. An authenticated attacker can manipulate their own subscription settings to reference another user's subscription and then infer that victim's subscription cost through the application's statistics output, exposing sensitive financial metadata without direct access to the victim's data.
Technical details
The vulnerability is a cross-user data isolation flaw in the subscription editing endpoint (POST /endpoints/subscription/add.php). An authenticated user can set the replacement_subscription_id field to reference any subscription ID, including those belonging to other users. The vulnerable code does not validate that the referenced subscription belongs to the requesting user. Later, when the stats calculation logic (includes/stats_calculations.php) performs a lookup to compute monthly-normalized costs, it queries the subscriptions table without scoping by user_id, allowing the attacker to infer the victim's subscription cost by observing deltas in their own stats output. Attack requires authentication and an inactive subscription to edit; no user interaction or social engineering is needed. The vulnerability was patched in version 4.9.1 by adding proper user_id scoping validation.
Affected products
- ellite Wallos prior to 4.9.1
Timeline
- 2026-05-27: disclosed: Version 4.9.1 released with patch
- 2026-06-01: advisory: GitHub Security Advisory GHSA-hggr-v8rm-c6jj published
- 2026-08-31: other: CVE-2026-50198 published