EUVD-2026-41964Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable endpoint requires authenticated client access (PR:L); no scope change, confidentiality, or availability impact; only invoice payment integrity (I:L) is affected.
Primary rating from Vendor (github).
CVSS VectorVendor: github
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
FOSSBilling's PayPalEmail payment adapter prior to version 0.8.0 fails to validate IPN-supplied payment amounts against invoice totals, enabling authenticated clients to underpay invoices while having them marked as fully paid. The PayPal IPN field mc_gross is credited directly to the client balance without cross-checking the corresponding invoice amount, and a pre-existing $0.05 floating-point epsilon in the credit-payment logic expands the exploitable gap to $0.04 per invoice. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the target FOSSBilling instance to have the PayPalEmail payment adapter explicitly configured and active - this is a non-default, operator-selected configuration. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 2.3 accurately reflects constrained real-world impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An authenticated FOSSBilling client generates an invoice for a subscription or service, selects PayPal as the payment method, and initiates a nominal payment through PayPal. The client then crafts or replays an IPN callback to the FOSSBilling endpoint with `mc_gross` set to a value $0.01-$0.04 below the invoice total; because no server-side amount validation occurs and the floating-point epsilon absorbs the difference, the invoice is marked fully paid. … |
| Remediation | Vendor-released patch: FOSSBilling 0.8.0. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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