CVE-2026-43927 — FOSSBilling has race condition in cart checkout that bypasses promo code usage limits

Description (CNA)

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.

Affected (CNA)

Vendor / product	Versions
FOSSBilling / FOSSBilling	affected < 0.8.0

CWE

CWE-367

References

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-w898-cx35-25gh

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.