CVE-2026-43928Network attack vector

Invoice underpayment via unchecked PayPal IPN amount

Published Jul 6, 2026 · Updated Jul 6, 2026

Improper payment validation in FOSSBilling before 0.8.0 allows remote authenticated users to underpay PayPalEmail invoices by up to $0.04. The PayPalEmail adapter credits IPN-supplied mc_gross without comparing it to the invoice total, and tryPayWithCredits treats balances less than $0.05 short as sufficient. A client account, a valid PayPal payment callback, and the PayPalEmail adapter are required; repeated abuse alters invoice status and causes bounded per-transaction merchant loss.

CVSS severity2.3
Low
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper payment validation in FOSSBilling before 0.8.0 allows remote authenticated users to underpay PayPalEmail invoices by up to $0.04. The PayPalEmail adapter credits IPN-supplied mc_gross without comparing it to the invoice total, and tryPayWithCredits treats balances less than $0.05 short as sufficient. A client account, a valid PayPal payment callback, and the PayPalEmail adapter are required; repeated abuse alters invoice status and causes bounded per-transaction merchant loss.

The record

CVE
CVE-2026-43928
Published
Jul 6, 2026
Updated
Jul 6, 2026
Vendor
FOSSBilling
Product
FOSSBilling
Classifications
CWE-1284, CWE-754, T1565.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.8.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

FOSSBilling · FOSSBillingversion=< 0.8.0

Published CVSS scores

2.3GitHubCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1284Improper Validation of Specified Quantity in Input
CWE-754Improper Check for Unusual or Exceptional Conditions
T1565.001Stored Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo