CVE-2026-77999Network attack vectorHinoki check available

Unpaid order confirmation via forged PayPal callbacks

Published Sep 3, 2026 · Updated Sep 3, 2026

PayPal callback forgery in J2Store 1.0.0 through 3.3.21, 4.0.0 through 4.0.21, and 4.1.0 through 4.1.6 allows remote attackers to alter orders. The _validateIPN() routine accepts unverified responses and its verdict is ignored; omitting mc_gross skips amount validation, while paypalv2.php never checks the amount. A public storefront with PayPal enabled and a configured receiver email permits anonymous requests to confirm unpaid orders or fail pending orders using an enumerated order ID.

CVSS severity8.7
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

PayPal callback forgery in J2Store 1.0.0 through 3.3.21, 4.0.0 through 4.0.21, and 4.1.0 through 4.1.6 allows remote attackers to alter orders. The _validateIPN() routine accepts unverified responses and its verdict is ignored; omitting mc_gross skips amount validation, while paypalv2.php never checks the amount. A public storefront with PayPal enabled and a configured receiver email permits anonymous requests to confirm unpaid orders or fail pending orders using an enumerated order ID.

The record

CVE
CVE-2026-77999
Published
Sep 3, 2026
Updated
Sep 3, 2026
Vendor
J2Commerce
Product
J2Store
Classifications
CWE-472, CWE-602, T1565.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=1.0.0-3.3.21
  2. Affected versionversion=4.0.0-4.0.21
  3. Affected versionversion=4.1.0-4.1.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

J2Commerce · J2Storeversion=1.0.0-3.3.21; version=4.0.0-4.0.21; version=4.1.0-4.1.6

Published CVSS scores

8.7Joomla CNACVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-472External Control of Assumed-Immutable Web Parameter
CWE-602Client-Side Enforcement of Server-Side Security
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

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Your stack

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