CVE Intelligence
Medium Info disclosure

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

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.

Published Oct 19, 2026 · Updated Oct 19, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.3% (30-day exploitation probability)+3
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.29%
ahead of 20% of scored CVEs · Oct 20, 2026
Affects
FOSSBilling
FOSSBilling
CVSS base
6.9
Medium · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (FOSSBilling FOSSBilling).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Search available logs for exploit probes matching the vulnerability class (info disclosure), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
FOSSBilling FOSSBilling version >= 0.1.0, < 0.8.7 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Attack requirements
None
Privileges required
None
User interaction
None
Scope
X
Confidentiality (vulnerable system)
Low
Integrity (vulnerable system)
None
Availability (vulnerable system)
None
Confidentiality (subsequent)
None
Integrity (subsequent)
None
Availability (subsequent)
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.9 CVSS 4.0 Medium — — security-advisories@github.com via NIST National Vulnerability Database
6.9 CVSS 4.0 Medium — — GitHub_M via CVE Program (cve.org) e CISA ADP
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/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 (score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-200 · Exposure of Sensitive Information

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Look for anomalous data read/export volumes and access to sensitive records.
web/proxy/WAF logsnetwork IDS/IPSapplication logsauthentication logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · fossbilling/fossbilling
    Oct 19, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 19, 2026
  • CVSS changed · 6.9
    Oct 19, 2026 · NIST National Vulnerability Database
  • Source status changed · → Deferred
    Oct 19, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 19, 2026 · NIST National Vulnerability Database
  • CVE published
    Oct 19, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 19, 2026 – Oct 19, 2026

References

4 on the record

Elsewhere on this site

FOSSBilling
every CVE for this vendor
Info disclosure
same class
CWE-200
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-111053 FOSSBilling: Unauthenticated attacker can probe existence of arbitrary files via guest/system/template_exists 1d
  • CVE-2026-111046 FOSSBilling: Low-privileged staff can read and modify configuration of deactivated extensions 1d
  • CVE-2026-53648 FOSSBilling: Downloadable product files can be overwritten through filename collisions Jul 6, 2026
  • CVE-2026-53647 FOSSBilling vulnerable to unauthenticated API key configuration disclosure via guest Serviceapikey get_info endpoint Jul 6, 2026
  • CVE-2026-53644 FOSSBilling's missing order-state validation allows clients to read and reset API key secrets for non-active orders Jul 6, 2026
  • CVE-2026-53642 FOSSBilling: Unverified clients can access client-area pages when email confirmation is required Jul 6, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No CISA SSVC assessment.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-111056 is "FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint", rated Medium. It affects FOSSBilling (FOSSBilling); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.9 describes technical severity. EPSS 0.29% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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