FOSSBilling up to 0.7.x Password Reset Confirmation Endpoint reset-password-confirm response discrepancy

Summaryinfo

A vulnerability marked as problematic has been reported in FOSSBilling up to 0.7.x. Affected is an unknown function of the file /client/reset-password-confirm of the component Password Reset Confirmation Endpoint. This manipulation causes response discrepancy. This vulnerability appears as CVE-2026-43926. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in FOSSBilling up to 0.7.x. It has been declared as problematic. Affected by this vulnerability is an unknown code of the file /client/reset-password-confirm of the component Password Reset Confirmation Endpoint. The manipulation with an unknown input leads to a response discrepancy vulnerability. The CWE definition for the vulnerability is CWE-204. The product provides different responses to incoming requests in a way that reveals internal state information to an unauthorized actor outside of the intended control sphere. As an impact it is known to affect confidentiality. The summary by CVE is:

FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the password reset confirmation endpoint `/client/reset-password-confirm/:hash` is handled by a non-API controller and is not covered by FOSSBilling's rate limiter, which only applies to `/api/*` routes. This allows an attacker to probe the endpoint for valid reset tokens without any per-IP request limiting, attempt counting, or lockout mechanism. The endpoint acts as an oracle, returning a distinguishable response for valid versus invalid tokens (HTTP 200 vs HTTP 302 redirect). An attacker can submit unlimited token guesses to the password reset confirmation endpoint with no throttling applied. However, practical exploitability is significantly mitigated by the current token generation, which uses `hash('sha256', random_bytes(32))`, providing 256 bits of entropy. Tokens also expire after 15 minutes and are deleted after successful use. The same architectural gap applies to other controller-served auth routes, including `/staff/email/:hash` (admin password reset confirmation) and `/client/confirm-email/:hash` (email confirmation). Version 0.8.0 fixes the issue. Some workarounds are available. Configure a reverse proxy (e.g., Nginx, Apache, Cloudflare) to apply per-IP rate limiting to the `/client/reset-password-confirm/*` and `/staff/email/*` paths and/or use a WAF rule to limit request rates to these endpoints.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-43926 since 05/04/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1592 according to MITRE ATT&CK.

Upgrading to version 0.8.0 eliminates this vulnerability.

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Productinfo

Type

• Billing Software

Name

• FOSSBilling

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7

Website

• Product: https://github.com/FOSSBilling/FOSSBilling/

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