Medium 6.9Published Oct 19, 2026

CVE-2026-111056FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint

Updated under an hour ago (2026-10-21 03:10 UTC)

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No exploitation reported and no EPSS estimate yet.

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Every CVE for FOSSBilling

Exploited in the last 30 days

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.

CVSS: 6.9 MEDIUM (v4.0, CNA)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
Weakness (CWE): CWE-200, CWE-204, CWE-307
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Oct 19, 2026
First seen by InfoSec Signals: Oct 19, 2026

Affected products

Affected products

FOSSBilling FOSSBilling fossbilling:fossbilling (from the name)	from 0.1.0, < 0.8.7	CNA record

References

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-x4mh-g4pc-wfc5x-refsource-confirm
https://github.com/FOSSBilling/FOSSBilling/pull/4234x-refsource-misc
https://github.com/FOSSBilling/FOSSBilling/commit/19f41ff0a45874c7362b7732c8f68db84bc59c55x-refsource-misc
https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.7x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.