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

Quick assessment

Affected
FOSSBilling FOSSBilling
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

fossbilling是fossbilling团队开源的一种高效计费和客户管理方案。 FOSSBilling 0.8.0之前版本存在竞争条件问题漏洞，该漏洞源于购物车结账流程中的竞争条件问题，可能导致已通过身份验证的客户端应用超过设最大使用次数的促销代码，获得无限制折扣或免费订单。

AI Predicted 6.5 Difficulty: Moderate EPSS 0.33% · P24

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
FOSSBilling FOSSBilling < 0.8.0 affected
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I. Basic Information for CVE-2026-43927

Vulnerability Information
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Vulnerability Title
FOSSBilling has race condition in cart checkout that bypasses promo code usage limits
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
检查时间与使用时间(TOCTOU)的竞争条件
Source: CVE Program / CVE List V5
Vulnerability Title
FOSSBilling 竞争条件问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
fossbilling是fossbilling团队开源的一种高效计费和客户管理方案。 FOSSBilling 0.8.0之前版本存在竞争条件问题漏洞，该漏洞源于购物车结账流程中的竞争条件问题，可能导致已通过身份验证的客户端应用超过设最大使用次数的促销代码，获得无限制折扣或免费订单。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
FOSSBilling FOSSBilling < 0.8.0 -

II. Public POCs for CVE-2026-43927

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III. Intelligence Information for CVE-2026-43927

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Vendor Advisories for CVE-2026-43927 (1)

Same Patch Batch · FOSSBilling · 2026-07-06 · 17 CVEs total

CVE-2026-42341 FOSSBilling has an unauthenticated payment bypass via IPN callback forgery
CVE-2026-42331 FOSSBilling missing authorization in guest Invoice API endpoints
CVE-2026-33734 FOSSBilling has improper SQL neutralization in `Massmailer` recipient filters
CVE-2026-43921 FOSSBilling vulnerable to arbitrary PHP code injection via unescaped config serialization
CVE-2026-43918 Suspended or inactive FOSSBilling accounts can retain or regain access through existing se
CVE-2026-43925 FOSSBilling: Mass assignment of group_id in guest client registration allows unauthorized
CVE-2026-43928 FOSSBilling: Payment amount not validated in PayPalEmail adapter allows invoice underpayme
CVE-2026-53640 FOSSBilling missing authorization checks on read-only admin API endpoints expose sensitive
CVE-2026-53641 FOSSBilling has stored XSS in client email views via unescaped content in JavaScript templ
CVE-2026-53645 FOSSBilling's missing self-edit prevention in staff permission management allows persisten
CVE-2026-53646 FOSSBilling: Client password reset token reuse allows persistent account takeover
CVE-2026-53643 FOSSBilling allows low-privileged staff accounts to perform unauthorized actions via admin
CVE-2026-53644 FOSSBilling's missing order-state validation allows clients to read and reset API key secr
CVE-2026-53642 FOSSBilling: Unverified clients can access client-area pages when email confirmation is re
CVE-2026-53647 FOSSBilling vulnerable to unauthenticated API key configuration disclosure via guest Servi
CVE-2026-53648 FOSSBilling: Downloadable product files can be overwritten through filename collisions

IV. Related Vulnerabilities

Same product: FOSSBilling
Same vendor: FOSSBilling
Same weakness: CWE-367

V. Comments for CVE-2026-43927

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