FOSSBilling up to 0.7.x Promo Code race condition

Summaryinfo

A vulnerability was found in FOSSBilling up to 0.7.x. It has been rated as critical. This affects an unknown part of the component Promo Code Handler. The manipulation leads to race condition. This vulnerability is referenced as CVE-2026-43927. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability was found in FOSSBilling up to 0.7.x and classified as critical. This issue affects an unknown function of the component Promo Code Handler. The manipulation with an unknown input leads to a race condition vulnerability. Using CWE to declare the problem leads to CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-43927 since 05/04/2026. The exploitation is known to be easy. The attack may be initiated remotely. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available.

Upgrading to version 0.8.0 eliminates this vulnerability.

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Productinfo

Type

• Billing Software

Name

• FOSSBilling

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7

Website

• Product: https://github.com/FOSSBilling/FOSSBilling/

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