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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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.
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.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-111053 being exploited?
There is no known exploitation of CVE-2026-111053 in the wild and no public exploit code.
Sources
Also known as GHSA-fm3x-cx5r-wwgp.