CVE-2026-111056 FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint
Unauthenticated attackers can enumerate registered client emails by analyzing error responses from the guest signup 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-2026-111056?
CVE-2026-111056 is a medium-severity 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 POST /api/guest/client/create endpoint reveals whether a submitted email belongs to a registered client because guest signup returns a distinct unredacted error when the submitted email already exists. The trigger is an unauthenticated request to POST /api/guest/client/create with a target email address. An attacker can compare the guest-signup response for a target email to determine whether the email belongs to an existing FOSSBilling client. Box\Mod\Client\Api\Guest::create returns the error after Client\Service::clientAlreadyExists finds a matching record, and the API response exposes that exception message without redaction. This issue is fixed in version 0.8.7.
Which versions are affected by CVE-2026-111056?
How do I fix CVE-2026-111056?
No fix has been published for CVE-2026-111056 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-111056 being exploited?
There is no known exploitation of CVE-2026-111056 in the wild and no public exploit code.
Sources
Also known as GHSA-x4mh-g4pc-wfc5.