# CVE-2026-43928 — FOSSBilling

> As of 2026-07-07, CVE-2026-43928 is a Low-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in FOSSBilling, CVSS v4.0 2.3, EPSS 0.2% (19.1th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-43928 as of 2026-07-07; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-07-07

## What is CVE-2026-43928?

FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the PayPalEmail payment adapter accepts PayPal IPN callbacks and credits the IPN-supplied amount (`mc_gross`) to the client's balance without validating it against the invoice total. Combined with a $0.05 floating-point epsilon tolerance in the invoice credit-payment logic, this allows a client to underpay an invoice by up to $0.04 and still have it marked as fully paid. Version 0.8.0 patches the issue. There is no effective workaround without modifying the source code. Merchants using the PayPalEmail adapter should monitor IPN transactions for amounts that do not match their corresponding invoice totals, and manually review and refund suspicious payments.

The record classifies CVE-2026-43928 under weakness classes [CWE-754](https://intel.threadlinqs.com/cwe/CWE-754), [CWE-1284](https://intel.threadlinqs.com/cwe/CWE-1284). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 91 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 2.3 — Low (derived from score) (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **EPSS (FIRST):** 0.2% probability of exploitation in the next 30 days, higher than 19.1% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 1.9/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-06, last modified 2026-07-07

## Is CVE-2026-43928 being exploited?

It currently carries a trending score of 34 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [FOSSBilling](https://intel.threadlinqs.com/vendors/fossbilling): FOSSBilling

## How to fix CVE-2026-43928

No vendor patch reference has been recorded for CVE-2026-43928 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-43928

No threat campaign in the Threadlinqs corpus currently references CVE-2026-43928, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-07-08. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com](https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-xjc6-g382-h942)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-43928
Full detection coverage and IOCs for threats exploiting CVE-2026-43928 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp