---
id: "CVE-2026-112374"
kind: "vulnerability"
aliases: ["CVE-2026-112374"]
title: "FOSSBilling: staff login form lets attackers force a victim's browser login"
severity: "medium"
cvss: 5.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["fossbilling", "package", "php", "self-hosted"]
not_affected_if: ["fossbilling-0.8.9-or-later"]
published_at: "2026-10-30T13:18:29+00:00"
first_seen_at: "2026-10-30T13:30:27+00:00"
updated_at: "2026-10-30T13:32:15+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112374", "first_seen_at": "2026-10-30T13:30:27+00:00"}]
---

# FOSSBilling: staff login form lets attackers force a victim's browser login

FOSSBilling before 0.8.9 accepts staff login requests at POST /api/guest/staff/login without CSRF or Origin checks. A malicious page can auto-submit a form that silently logs a visitor's browser into an attacker-controlled staff account.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed FOSSBilling version and confirm it is below `0.8.9`.
- Look for the route `/api/guest/staff/login` in the deployed code or web server logs.

## Fix

- Move FOSSBilling to `0.8.9` or later, per the NVD description.

## Timeline

- 2026-10-30T13:30:27+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112374

## From the sources

FOSSBilling before 0.8.9 contains a Cross-Site Request Forgery vulnerability in the staff guest login endpoint (POST /api/guest/staff/login) that allows remote attackers to force authentication because checkGuestClientAuthentication() only allowlists client_login and client_create, leaving staff_login without CSRF or Origin validation. Attackers can host an auto-submitting HTML form with attacker-controlled credentials to silently log a victim's browser into the attacker's staff account.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_