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CWE-367Weakness · CWE-367

CVE-2026-43927

MEDIUM · 6.9 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 →
78/100
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, a race condition in the cart checkout flow allows an authenticated client to apply a promo code beyond its configured maximum uses. By sending concurrent checkout requests before any single request completes the usage increment, a client can obtain unlimited discounted or free orders from a single-use or limited-use promo code. Version 0.8.0 patches the issue. Some workarounds are available. Disable promo codes entirely until a patch is available or monitor the `promo` table for `used` values exceeding `maxuses` and manually review affected orders.

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

FOSSBilling prior to 0.8.0 contains a race condition in the cart checkout flow where concurrent checkout requests can bypass promo code usage limits. By sending multiple simultaneous requests before the usage counter increments, an authenticated client can apply a single-use or limited-use promo code unlimited times, resulting in discounted or free orders.

MitigationUpgrade to FOSSBilling 0.8.0 or later. Workarounds include disabling promo codes entirely or manually monitoring the promo table for rows where 'used' exceeds 'maxuses'.

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: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

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 installed FOSSBilling version
    Locate the version file (typically version.php or similar in the installation root, or check the database settings table for version metadata). Compare the version number to 0.8.0.
    Affected if The installed version is prior to 0.8.0 (e.g., 0.7.x, 0.6.x, etc.).
  2. Verify promo codes module is enabled
    Navigate to the admin dashboard settings or inspect the database 'extension' or 'config' table to confirm whether the 'promo' or 'coupon' module is active and set to 'enabled'.
    Affected if The promo codes module is currently enabled.
  3. Check for active promo codes with usage limits
    Query the promo codes table (commonly named 'promo' or 'coupon') to list all promo codes. Identify any codes where 'maxuses' is set to a finite value (greater than 0) or where 'type' indicates limited usage.
    Affected if There exist active promo codes that have a defined 'maxuses' limit.
  4. Inspect promo code usage against limits
    For each limited-use promo code, compare the current 'used' counter to the 'maxuses' value. Look for discrepancies where 'used' equals or exceeds 'maxuses', or check if the usage tracking mechanism appears vulnerable to race conditions (concurrent increments).
    Affected if The 'used' count exceeds the 'maxuses' limit for any promo code, indicating the race condition may have been exploited, or the usage counter logic lacks atomic transaction protection.

If FOSSBilling version is below 0.8.0, the promo codes module is enabled, and limited-use promo codes exist in the system, the environment is vulnerable to the race condition described in CVE-2026-43927.

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 0.8.0 or later. Workarounds include disabling promo codes entirely or manually monitoring the promo table for rows where 'used' exceeds 'maxuses'.

Recommended fix High confidence

FOSSBilling version 0.8.0

  1. Back up your FOSSBilling installation and database before proceeding with any updates
  2. Download FOSSBilling version 0.8.0 from the official GitHub repository (github.com)
  3. Upgrade your FOSSBilling installation to version 0.8.0 following the standard upgrade procedure
  4. After upgrade, query the `promo` table to identify any promo codes where `used` > `maxuses`
  5. Manually review and reverse any orders obtained through exploitation of the race condition
  6. Implement ongoing monitoring: periodically check the `promo` table for `used` values exceeding `maxuses`

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2026-43927 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data