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Missing AuthenticationWeakness · CWE-306

CVE-2026-42331

HIGH · 7.7 CVSS v4.0 Published 2026-07-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
86/100
Remediation priority · High
Remotely reachable No privileges Zero-click 7 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the Guest API invoice/update endpoint is missing an authorization check present in other invoice-related endpoints, allowing an unauthenticated user with knowledge of an invoice hash to modify the payment gateway associated with an unpaid invoice. An attacker who obtains an invoice hash, which may leak through shared URLs, referrer headers, or email links, can change the `gateway_id` on an unpaid invoice to any payment gateway configured in the system. This does not allow redirecting payments to an arbitrary external endpoint, as the gateway must already be installed and configured by an administrator. The practical impact is further limited by the `invoice_accessible_from_hash` system setting. Version 0.8.0 contains a patch. No known workarounds are available.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The Guest API invoice/update endpoint in FOSSBilling versions prior to 0.8.0 lacks an authorization check present in other invoice-related endpoints, allowing unauthenticated attackers with knowledge of an invoice hash to modify the payment gateway (gateway_id) on unpaid invoices.

MitigationUpgrade to FOSSBilling version 0.8.0 or later which contains the patch; no workarounds are available.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:H/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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify FOSSBilling installation and version
    Locate the FOSSBilling installation directory and check the version file (commonly version.php or similar version indicator in the root directory or composer.json)
    Affected if The installed version is prior to 0.8.0
  2. Determine if Guest API is enabled
    Check the API configuration file (typically in src/Config or similar directory) for settings related to guest API access, looking for 'guest_api' or 'api_guest' configuration keys
    Affected if Guest API access is enabled and accessible without authentication
  3. Verify invoice update endpoint accessibility
    Test whether the /api/guest/invoice/update endpoint responds without providing valid authentication credentials (api_key or session token)
    Affected if The endpoint returns a successful response instead of an authentication error
  4. Check if unpaid invoices exist
    Query the database (if accessible) or examine invoice records to identify unpaid invoices that could be targets
    Affected if There are unpaid invoices in the system with accessible hash identifiers

A FOSSBilling installation is affected if it is running any version prior to 0.8.0 with the Guest API enabled and the invoice/update endpoint accessible without authentication.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to FOSSBilling version 0.8.0 or later which contains the patch; no workarounds are available.

Recommended fix High confidence

0.8.0

  1. 1. Identify the current installed version of FOSSBilling by checking the installation directory or admin panel.
  2. 2. Back up the entire FOSSBilling installation including database before performing any upgrade.
  3. 3. Download FOSSBilling version 0.8.0 from the official GitHub repository (github.com/FOSSBilling/FOSSBilling).
  4. 4. Replace the existing FOSSBilling files with the new version 0.8.0 files, preserving configuration files and any custom modifications.
  5. 5. Run any database migration scripts included in the 0.8.0 release if applicable.
  6. 6. Verify the upgrade was successful by checking the admin panel shows version 0.8.0.
  7. 7. Test that the invoice/update endpoint now requires proper authorization before allowing modifications.

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation1.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,220
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42331 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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