CVE-2026-43928

Home/CVE/FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the PayPalEmail payment

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FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the PayPalEmail payment

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.

EPSS 0.00274

EPSS exploitation odds0.27% · top 80%

Monitor

⚠ NVD has not scored this CVE yet - manual triage required (common for recent CVEs)

Sigma rules0 YARA rules0

Look this up elsewhere - one-click external pivots

NVD CVE.org CISA Exploit-DB GitHub PoC VulnCheck KEV GreyNoise

▸ How to read a CVE - triage first, then detect and patch

This page is every public fact about CVE-2026-43928, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.

Triage: should I act now? Four signals, and they are not interchangeable:

CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.

How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.

Then what - two workflows:

Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.

Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).

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Severity & exploitation scoring

EPSS exploitation probability

0.27%

Top 80%odds of exploitation in the next 30 days

CVSS metric silhouette

No structured CVSS vector for this CVE. Older entries often have only a numeric base score - the metric breakdown radar requires a full AV:_/AC:_/... vector string published by NVD.

SSVC triage

No SSVC vulnrichment for this CVE. CISA's Vulnrichment program scores newer CVEs (~2024 onwards) plus selected older critical ones. Use the EPSS probability + KEV status to triage instead.

⬡

Weakness Classification

CWE-1284Improper Validation of Specified Quantity in Input

CWE-754Improper Check for Unusual or Exceptional Conditions

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Related CVEs

CVEs linked to this one by a shared weakness (CWE) or affected product - joins on data already in the engine, with the reason shown per row.

CVE-2008-1440 Microsoft Windows XP SP2 and SP3, and Server 2003 SP1 and SP2, does not properly... same CWE-1284 CVE-2008-2374 src/sdp.c in bluez-libs 3.30 in BlueZ, and other bluez-libs before 3.34 and blue... same CWE-1284 CRITICAL CVE-2009-4488 Varnish 2.0.6 writes data to a log file without sanitizing non-printable charact... 1 same CWE-1284 CRITICAL CVE-2010-3904 The rds_page_copy_user function in net/rds/page.c in the Reliable Datagram Socke... 2 same CWE-1284 HIGH CVE-2014-1737 The raw_cmd_copyin function in drivers/block/floppy.c in the Linux kernel throug... same CWE-754 CVE-2016-8209 Improper checks for unusual or exceptional conditions in Brocade NetIron 05.8.00... same CWE-754 HIGH CVE-2017-0610 An elevation of privilege vulnerability in the Qualcomm sound driver could enabl... same CWE-754 HIGH CVE-2017-11144 In PHP before 5.6.31, 7.x before 7.0.21, and 7.1.x before 7.1.7, the openssl ext... same CWE-754 HIGH

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References & Sources

Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-xjc6-g382-h942