CVE-2026-63100 Overview
CVE-2026-63100 is a missing authorization vulnerability in the Maybe personal finance application through version 0.6.0. The flaw resides in Settings::HostingsController, where the before_action ensure_admin filter is applied only to the clear_cache action. As a result, the show and update actions remain accessible to any authenticated user holding the member role. Attackers can read the operator's Synth API key in plaintext, overwrite it with an attacker-controlled value, toggle public registration, and disable email confirmation. The issue is classified under CWE-862: Missing Authorization.
Critical Impact
Low-privilege authenticated users can extract the Synth API key, hijack instance-wide hosting settings, and disrupt the entire deployment.
Affected Products
- Maybe (self-hosted personal finance application)
- All releases through version 0.6.0
- Deployments exposing the Settings::HostingsController endpoints
Discovery Timeline
- 2026-07-17 - CVE-2026-63100 published to NVD
- 2026-07-21 - Last updated in NVD database
Technical Details for CVE-2026-63100
Vulnerability Analysis
The vulnerability stems from an incomplete authorization filter in the Settings::HostingsController controller. In a correctly hardened controller, before_action :ensure_admin should protect every action that reads or mutates instance-wide configuration. In Maybe through 0.6.0, the filter is scoped only to clear_cache, leaving show and update reachable by any authenticated session, including the default member role.
The show action renders the hosting settings page and embeds the current Synth API key as the value attribute of a form field. Any authenticated user can request the page and read the key directly from the rendered HTML. The update action accepts a standard Rails form submission, allowing attackers to write arbitrary values back to the same settings record.
Because the affected controller governs global hosting behavior, a successful request modifies state for every user of the instance. Attackers can pivot from a low-privilege account to full operational disruption without triggering any admin-level check.
Root Cause
The root cause is a broken access control pattern in which authorization enforcement is opt-in per action rather than default-deny. The developer applied ensure_admin only to clear_cache, presumably to protect a destructive operation, and left show and update unguarded despite their equivalent privilege requirements. This matches the [CWE-862] pattern of missing authorization on sensitive endpoints.
Attack Vector
Exploitation requires only a valid member-role session, which is trivially obtained on any instance with public registration enabled. The attacker authenticates, issues a GET request to the hosting settings path, and parses the response HTML to recover the Synth API key rendered in the form. The attacker then submits a POST or PATCH request to the update action with modified parameters, overwriting the Synth API key, enabling public registration, and disabling email confirmation. Each request travels over the standard authenticated HTTP session, so no protocol-level anomaly is required.
No verified exploit code is available at this time. Refer to the VulnCheck Security Advisory and the GitHub Project Documentation for technical details.
Detection Methods for CVE-2026-63100
Indicators of Compromise
- Unexpected GET requests to the Settings::HostingsController#show route originating from non-admin user sessions.
- PATCH or PUT requests to the hosting settings update action from accounts without administrative role assignment.
- Sudden changes to the stored Synth API key value, particularly outside of planned maintenance windows.
- Configuration flips enabling public registration or disabling email confirmation without a corresponding admin audit entry.
Detection Strategies
- Correlate application access logs against user role metadata to identify member-role principals hitting admin-scoped controller paths.
- Enable Rails audit logging on the Setting model to record every write to hosting configuration attributes.
- Alert on outbound API traffic to Synth using unexpected keys, which indicates the API key has been rotated by an attacker.
Monitoring Recommendations
- Ship web server and Rails application logs to a centralized analytics platform and query for hosting settings endpoints accessed by non-admin sessions.
- Track configuration drift on the hosting settings record and generate alerts on any change to registration or email confirmation flags.
- Monitor authentication events for newly created accounts followed rapidly by requests to settings endpoints.
How to Mitigate CVE-2026-63100
Immediate Actions Required
- Restrict network access to Maybe instances until an upstream patch is deployed and verified.
- Rotate the Synth API key immediately and revoke any key that may have been exposed through the vulnerable form field.
- Disable public registration and audit existing user accounts for unexpected member-role additions.
- Review the hosting settings record for tampered values, including registration flags and email confirmation requirements.
Patch Information
At the time of publication, no fixed release is referenced in the NVD entry. Track the GitHub Project Documentation and the VulnCheck Security Advisory for a patched version. Operators should upgrade beyond 0.6.0 once a release corrects the before_action filter to cover show and update.
Workarounds
- Apply a local patch that adds before_action :ensure_admin to all actions in Settings::HostingsController, or restricts the filter with except: [] rather than an explicit action list.
- Place the instance behind a reverse proxy that denies non-admin sessions from reaching the /settings/hostings path.
- Remove sensitive values such as the Synth API key from rendered form fields and require re-entry on update to prevent plaintext disclosure.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
