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

[Starburst-David]

CVE ID: CVE-2026-43927
Published: July 6, 2026
Description: 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.
Severity: 6.9 | MEDIUM

More Information:
https://cvefeed.io/vuln/detail/CVE-2026-43927