CVE-2026-111056
FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint
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.
INFO
Published Date :
Oct. 19, 2026, 4:17 p.m.
Last Modified :
Oct. 19, 2026, 4:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Update FOSSBilling to version 0.8.7 or later.
- Apply vendor security patches promptly.
- Restrict access to the /api/guest/client/create endpoint.
- Monitor API responses for sensitive information.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-111056.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-111056 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-111056
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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The following list is the news that have been mention
CVE-2026-111056 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-111056 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by [email protected]
Oct. 19, 2026
Action Type Old Value New Value Added 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. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-200 Added CWE CWE-204 Added CWE CWE-307 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/111xxx/CVE-2026-111056.json">CVE-2026-111056</a> Added Reference https://github.com/FOSSBilling/FOSSBilling/commit/19f41ff0a45874c7362b7732c8f68db84bc59c55 Added Reference https://github.com/FOSSBilling/FOSSBilling/pull/4234 Added Reference https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.7 Added Reference https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-x4mh-g4pc-wfc5