# CVE-2026-111053: FOSSBilling: Unauthenticated attacker can probe existence of arbitrary files via guest/system/template_exists

> Unauthenticated attackers can determine the existence of arbitrary files on the server via path traversal in the template_exists endpoint.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-fm3x-cx5r-wwgp

## What is CVE-2026-111053?

CVE-2026-111053 is a medium-severity path traversal vulnerability in FOSSBilling, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-111053?


## How do I fix CVE-2026-111053?

No fix has been published for CVE-2026-111053 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-111053 being exploited?

There is no known exploitation of CVE-2026-111053 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-111053 and fix it if it is affected.

What it is: CVE-2026-111053 is a medium-severity path traversal vulnerability in FOSSBilling, published on 19 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-111053 in the wild and no public exploit code.

Affected product: FOSSBilling. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-111053/ (Markdown: https://insights.sbomify.com/CVE-2026-111053/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-111053
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-111053
- OSV: https://osv.dev/vulnerability/CVE-2026-111053

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-111053/
Summaries are generated and may contain mistakes; the official description above is the record.