---
id: "CVE-2026-111053"
kind: "vulnerability"
aliases: ["CVE-2026-111053"]
title: "FOSSBilling: unauthenticated endpoint reveals whether server files exist"
severity: "medium"
cvss: 6.9
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["billing", "fossbilling", "package", "php", "self-hosted"]
not_affected_if: ["auth-required", "managed-hosting"]
published_at: "2026-10-19T16:17:03+00:00"
first_seen_at: "2026-10-23T21:57:18+00:00"
updated_at: "2026-10-25T03:40:46+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-111053", "first_seen_at": "2026-10-23T21:57:18+00:00"}]
---

# FOSSBilling: unauthenticated endpoint reveals whether server files exist

FOSSBilling's guest template_exists endpoint joins an attacker-supplied file path without stripping traversal sequences, so anyone can probe the server. The endpoint returns only a true or false answer, so an attacker learns whether arbitrary files or directories exist but cannot read their contents.

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

## How to check

- Check the installed FOSSBilling version in the admin panel or in the project's version file; affected versions are `0.1.0` through `0.8.7` inclusive.
- Look for requests to `api/guest/system/template_exists` containing `..` in web server access logs.

## Fix

- Upgrade FOSSBilling to `0.8.7` or later.

## Timeline

- 2026-10-23T21:57:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-111053

## From the sources

FOSSBilling is an open source billing and client-management platform. From 0.1.0 until 0.8.7, the unauthenticated api/guest/system/template_exists endpoint permits path traversal because templateExists uses Path::join on the attacker-controlled file parameter without rejecting .. sequences or verifying that the resolved path remains inside the active theme directory. The trigger is an unauthenticated request to guest/system/template_exists containing traversal sequences in the file parameter. An attacker can submit traversal sequences in the file parameter and observe the returned boolean to determine whether arbitrary files or directories exist on the server. The oracle does not disclose file contents. This issue is fixed in version 0.8.7.

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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_