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TI-2026-76428 Aliases CVE-2026-111056

FOSSBilling guest signup enables client account enumeration

Priority LOW 36CWE-200Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Information disclosure, Security bypass
Confidentiality · integrity · availability
Low · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-200 and CWE-307.

Summary

FOSSBilling from 0.1.0 before 0.8.7 is affected. The unauthenticated POST /api/guest/client/create endpoint returns a distinct, unredacted error when the submitted email already belongs to a registered client, so the response reveals whether an address is a client. An unauthenticated remote attacker can send guest signup requests for target addresses and compare the responses, and the CVSS 4.0 rating is 6.9 (MEDIUM). The weakness is classified as CWE-200.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00285 21st percentileScored 2026-11-07
Fix Fixed FOSSBilling (FOSSBilling): 0.8.7

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
FOSSBillingFOSSBilling0.1.0 to before 0.8.70.8.7Patch availableCNA
  • FOSSBilling VendorFOSSBilling Affected 0.1.0 to before 0.8.7 Fixed in 0.8.7 Patch available CNA

Remediation

Upgrade to FOSSBilling 0.8.7, the version that fixes this issue. The affected range is listed with the status no_fix_listed, so no fixed version is listed for releases before 0.8.7.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

  • Fix · CNA FOSSBilling (FOSSBilling) Fixed in 0.8.7

Timeline

  1. 2026-10-19 Threatist record created from CVE-2026-111056
  2. 2026-10-21 Priority changed: MEDIUM → LOW
  3. 2026-10-22 CISA SSVC decision points changed

References

Other 4

  • TI-2023-03258 SQL Injection in fossbilling/fossbilling CVSS 3.1CRITICAL 9.8
  • TI-2023-03719 Insufficient Session Expiration in fossbilling/fossbilling CVSS 3.1CRITICAL 9.8
  • TI-2023-03259 Unrestricted Upload of File with Dangerous Type in fossbilling/fossbilling CVSS 3.1HIGH 8.8
  • TI-2023-03261 Improper Neutralization of Formula Elements in a CSV File in fossbilling/fossbilling CVSS 3.1HIGH 8.0
  • TI-2026-30636 FOSSBilling missing authorization in guest Invoice API endpoints CVSS 4.0HIGH 7.7
  • TI-2023-03173 Code Injection in fossbilling/fossbilling CVSS 3.1HIGH 7.2
See all 43 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences