CVE-2026-77999

HIGHPre-NVD 8.78.7—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.7 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 83% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this week
8.7EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.7Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Joomla Extension - j2commerce.com - Unauthenticated PayPal callback forgery leading to order confirmation fraud in J2Store 1.0.0-3.3.21, 4.0.0-4.0.21, 4.1.0-4.1.6 - The PayPal IPN listener's signature check (_validateIPN()) accepted UNVERIFIED and any non-INVALID response as valid, made its verification request with CURLOPT_SSL_VERIFYPEER disabled, and stored its verdict in a field nothing downstream ever checked — so processing continued regardless of the outcome. Separately, the paid-amount comparison only ran when mc_gross was a positive number; omitting the field from the POST body (floatval(null) == 0) skipped the check entirely. Combined with a merchant-configured receiver_email and a sequential, enumerable order id read from the custom field, an anonymous POST was enough to move a pending order straight to CONFIRMED with no payment, or force another customer's pending order to FAILED. paypalv2.php performed no amount check under any circumstances.

CVSS v3
8.7
EG Score
8.7(medium)
EG Risk
54(Track)
EG Risk 54/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity87% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
17%
KEV
Not listed

Published

September 3, 2026

Last Modified

September 3, 2026

Advisory Details (1)

Auto-updated Sep 3, 2026
No patch confirmed yet.
generic

Powerful and intuitive Joomla eCommerce. - J2Commerce

https://www.j2commerce.com/

Vendor Advisories for CVE-2026-77999(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 26× in last 7d / 60× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-19 00:31 UTCEG score recompute
  2. 2026-09-19 00:31 UTCGHSA enrichment
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-18 12:25 UTCGHSA enrichment
  5. 2026-09-18 00:23 UTCEG score recompute
  6. 2026-09-18 00:23 UTCGHSA enrichment
  7. 2026-09-17 12:20 UTCGHSA enrichment
  8. 2026-09-17 00:18 UTCEG score recompute
  9. 2026-09-17 00:18 UTCGHSA enrichment
  10. 2026-09-16 14:08 UTCEPSS rescore
  11. 2026-09-16 12:15 UTCEG score recompute
  12. 2026-09-16 12:15 UTCGHSA enrichment
  13. 2026-09-16 05:15 UTCEPSS rescore
  14. 2026-09-16 00:12 UTCGHSA enrichment
  15. 2026-09-15 12:10 UTCEG score recompute
  16. 2026-09-15 12:10 UTCGHSA enrichment
  17. 2026-09-15 03:12 UTCEPSS rescore
  18. 2026-09-15 03:12 UTCEPSS rescore
  19. 2026-09-15 00:08 UTCGHSA enrichment
  20. 2026-09-14 12:06 UTCGHSA enrichment
  21. 2026-09-14 00:04 UTCEG score recompute
  22. 2026-09-14 00:04 UTCGHSA enrichment
  23. 2026-09-13 12:02 UTCGHSA enrichment
  24. 2026-09-13 00:00 UTCEG score recompute
  25. 2026-09-13 00:00 UTCGHSA enrichment
Show 35 more
  1. 2026-09-12 11:58 UTCGHSA enrichment
  2. 2026-09-11 23:55 UTCEG score recompute
  3. 2026-09-11 23:55 UTCGHSA enrichment
  4. 2026-09-11 14:53 UTCEPSS rescore
  5. 2026-09-11 14:53 UTCEPSS rescore
  6. 2026-09-11 11:53 UTCEG score recompute
  7. 2026-09-11 11:53 UTCGHSA enrichment
  8. 2026-09-10 23:51 UTCGHSA enrichment
  9. 2026-09-10 11:33 UTCEG score recompute
  10. 2026-09-10 11:32 UTCGHSA enrichment
  11. 2026-09-10 09:35 UTCEPSS rescore
  12. 2026-09-09 23:29 UTCGHSA enrichment
  13. 2026-09-09 11:12 UTCGHSA enrichment
  14. 2026-09-08 23:10 UTCEG score recompute
  15. 2026-09-08 23:10 UTCGHSA enrichment
  16. 2026-09-08 22:01 UTCEPSS rescore
  17. 2026-09-08 06:08 UTCGHSA enrichment
  18. 2026-09-07 18:02 UTCEG score recompute
  19. 2026-09-07 18:02 UTCGHSA enrichment
  20. 2026-09-07 05:59 UTCGHSA enrichment
  21. 2026-09-06 17:58 UTCEG score recompute
  22. 2026-09-06 17:58 UTCGHSA enrichment
  23. 2026-09-06 13:48 UTCEPSS rescore
  24. 2026-09-06 05:55 UTCGHSA enrichment
  25. 2026-09-05 17:53 UTCEG score recompute
  26. 2026-09-05 17:52 UTCGHSA enrichment
  27. 2026-09-05 05:49 UTCGHSA enrichment
  28. 2026-09-04 17:46 UTCEG score recompute
  29. 2026-09-04 17:46 UTCGHSA enrichment
  30. 2026-09-04 05:43 UTCGHSA enrichment
  31. 2026-09-03 17:38 UTCGHSA enrichment
  32. 2026-09-03 13:14 UTCEG score recompute
  33. 2026-09-03 12:48 UTCEG score recompute
  34. 2026-09-03 12:01 UTCEG score recompute
  35. 2026-09-03 11:59 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-77999?
CVE-2026-77999 is a high vulnerability published on September 3, 2026. Joomla Extension - j2commerce.com - Unauthenticated PayPal callback forgery leading to order confirmation fraud in J2Store 1.0.0-3.3.21, 4.0.0-4.0.21, 4.1.0-4.1.6 - The PayPal IPN listener's signature check (validateIPN()) accepted UNVERIFIED and any non-INVALID response as valid, made its…
When was CVE-2026-77999 disclosed?
CVE-2026-77999 was first published in the National Vulnerability Database on September 3, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-77999 actively exploited?
CVE-2026-77999 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 82.9% of all scored CVEs.
What is the CVSS score of CVE-2026-77999?
CVE-2026-77999 has a CVSS v3 base score of 8.7 (NVD).
How do I remediate CVE-2026-77999?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-77999, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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