CVE-2026-8421

HIGHNVD 8.88.8—
EchelonGraph scoreMEDIUM confidence

Score 8.8 from GitHub Security Advisory (severity: HIGH) published 2026-05-21. NVD baseline CVSS 8.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
8.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 8.8Exploit: NoneExposed: 0

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

Concrete CMS 9.5.0 and below contains a CSRF vulnerability in the install_package() method of concrete/controllers/single_page/dashboard/extend/install.php.  An attacker who can cause an authenticated administrator to visit a crafted page,  and who has placed or caused a package to be present under DIR_PACKAGES//, can force the installation of that package without any CSRF protection. Package installation executes the package controller's install() method as the web server user, enabling remote code execution.  In order to be vulnerable, the victim must be passing canInstallPackages. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 7.5 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks  https://github.com/maru1009  for reporting.

CVSS v3
8.8
EG Score
8.8(medium)
EPSS
6.7%
KEV
Not listed

Published

May 21, 2026

Last Modified

May 26, 2026

Advisory Details (1)

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

9.5.1 Release Notes :: Concrete CMS

https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes

Vendor Advisories for CVE-2026-8421(1)

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

Affected Packages

(1 across 1 ecosystem)
Packagist(1)
PackageVulnerable rangeFixed inDependents
concrete5/concrete58.0 ... 9.5.0RC2 (89 versions)9.5.1—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 6× in last 7d / 48× 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.

Showing the most recent 100 of 139 total refreshes for this CVE.

  1. 2026-07-15 16:57 UTCEPSS rescore
  2. 2026-07-15 02:00 UTCEPSS rescore
  3. 2026-07-13 22:31 UTCEPSS rescore
  4. 2026-07-13 06:13 UTCEPSS rescore
  5. 2026-07-11 08:27 UTCEPSS rescore
  6. 2026-07-09 19:10 UTCEPSS rescore
  7. 2026-07-08 15:16 UTCEPSS rescore
  8. 2026-07-07 13:46 UTCEPSS rescore
  9. 2026-07-07 13:46 UTCEPSS rescore
  10. 2026-07-06 16:27 UTCEPSS rescore
  11. 2026-07-06 16:27 UTCEPSS rescore
  12. 2026-07-06 02:23 UTCEPSS rescore
  13. 2026-07-06 02:23 UTCEPSS rescore
  14. 2026-07-05 02:31 UTCEPSS rescore
  15. 2026-07-05 02:30 UTCEPSS rescore
  16. 2026-07-04 06:31 UTCEPSS rescore
  17. 2026-07-04 06:31 UTCEPSS rescore
  18. 2026-07-01 15:07 UTCEPSS rescore
  19. 2026-06-30 23:22 UTCEPSS rescore
  20. 2026-06-29 19:55 UTCEG score recompute
  21. 2026-06-29 14:06 UTCEPSS rescore
  22. 2026-06-28 14:07 UTCEPSS rescore
  23. 2026-06-28 07:51 UTCEG score recompute
  24. 2026-06-28 04:56 UTCEPSS rescore
  25. 2026-06-27 19:33 UTCEG score recompute
Show 75 more
  1. 2026-06-27 07:22 UTCEG score recompute
  2. 2026-06-27 03:08 UTCEPSS rescore
  3. 2026-06-26 19:18 UTCEG score recompute
  4. 2026-06-26 03:25 UTCEG score recompute
  5. 2026-06-25 14:14 UTCEG score recompute
  6. 2026-06-25 13:50 UTCEPSS rescore
  7. 2026-06-24 14:05 UTCEPSS rescore
  8. 2026-06-23 21:33 UTCEPSS rescore
  9. 2026-06-22 14:25 UTCEPSS rescore
  10. 2026-06-21 14:56 UTCEPSS rescore
  11. 2026-06-21 01:59 UTCEPSS rescore
  12. 2026-06-19 19:26 UTCEPSS rescore
  13. 2026-06-18 17:52 UTCEPSS rescore
  14. 2026-06-17 22:39 UTCEG score recompute
  15. 2026-06-17 22:39 UTCGHSA enrichment
  16. 2026-06-17 17:53 UTCEPSS rescore
  17. 2026-06-17 11:07 UTCEG score recompute
  18. 2026-06-17 11:07 UTCGHSA enrichment
  19. 2026-06-16 19:42 UTCEG score recompute
  20. 2026-06-16 19:42 UTCGHSA enrichment
  21. 2026-06-16 17:53 UTCEPSS rescore
  22. 2026-06-16 02:59 UTCEG score recompute
  23. 2026-06-16 02:59 UTCGHSA enrichment
  24. 2026-06-15 17:49 UTCEPSS rescore
  25. 2026-06-15 17:49 UTCEPSS rescore
  26. 2026-06-15 15:37 UTCEG score recompute
  27. 2026-06-15 15:37 UTCGHSA enrichment
  28. 2026-06-15 00:57 UTCEG score recompute
  29. 2026-06-15 00:57 UTCGHSA enrichment
  30. 2026-06-14 23:18 UTCEPSS rescore
  31. 2026-06-14 13:34 UTCEG score recompute
  32. 2026-06-14 13:34 UTCGHSA enrichment
  33. 2026-06-14 02:12 UTCEG score recompute
  34. 2026-06-14 02:12 UTCGHSA enrichment
  35. 2026-06-13 23:00 UTCEPSS rescore
  36. 2026-06-13 14:51 UTCEG score recompute
  37. 2026-06-13 14:51 UTCGHSA enrichment
  38. 2026-06-13 03:30 UTCEG score recompute
  39. 2026-06-13 03:29 UTCGHSA enrichment
  40. 2026-06-12 23:12 UTCEPSS rescore
  41. 2026-06-12 23:12 UTCEPSS rescore
  42. 2026-06-12 15:40 UTCEG score recompute
  43. 2026-06-12 15:40 UTCGHSA enrichment
  44. 2026-06-12 04:06 UTCEG score recompute
  45. 2026-06-12 04:06 UTCGHSA enrichment
  46. 2026-06-11 16:44 UTCEG score recompute
  47. 2026-06-11 16:44 UTCGHSA enrichment
  48. 2026-06-11 14:00 UTCEPSS rescore
  49. 2026-06-11 04:07 UTCEG score recompute
  50. 2026-06-11 04:07 UTCGHSA enrichment
  51. 2026-06-10 22:19 UTCEPSS rescore
  52. 2026-06-10 16:46 UTCEG score recompute
  53. 2026-06-10 16:46 UTCGHSA enrichment
  54. 2026-06-10 13:22 UTCEPSS rescore
  55. 2026-06-10 05:25 UTCEG score recompute
  56. 2026-06-10 05:25 UTCGHSA enrichment
  57. 2026-06-09 18:04 UTCEG score recompute
  58. 2026-06-09 18:04 UTCGHSA enrichment
  59. 2026-06-09 06:43 UTCEG score recompute
  60. 2026-06-09 06:43 UTCGHSA enrichment
  61. 2026-06-08 19:21 UTCEG score recompute
  62. 2026-06-08 19:21 UTCGHSA enrichment
  63. 2026-06-08 14:17 UTCEPSS rescore
  64. 2026-06-08 04:54 UTCEG score recompute
  65. 2026-06-08 04:54 UTCGHSA enrichment
  66. 2026-06-07 17:33 UTCEG score recompute
  67. 2026-06-07 17:33 UTCGHSA enrichment
  68. 2026-06-07 15:25 UTCEPSS rescore
  69. 2026-06-07 06:12 UTCEG score recompute
  70. 2026-06-07 06:12 UTCGHSA enrichment
  71. 2026-06-06 18:51 UTCEG score recompute
  72. 2026-06-06 18:51 UTCGHSA enrichment
  73. 2026-06-06 13:47 UTCEPSS rescore
  74. 2026-06-06 07:30 UTCEG score recompute
  75. 2026-06-06 07:30 UTCGHSA enrichment

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-8421?
CVE-2026-8421 is a high vulnerability published on May 21, 2026. Concrete CMS 9.5.0 and below contains a CSRF vulnerability in the installpackage() method of concrete/controllers/singlepage/dashboard/extend/install.php. An attacker who can cause an authenticated administrator to visit a crafted page, and who has placed or caused a package to be present under…
When was CVE-2026-8421 disclosed?
CVE-2026-8421 was first published in the National Vulnerability Database on May 21, 2026, with the most recent update on May 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-8421 actively exploited?
CVE-2026-8421 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 6.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-8421?
CVE-2026-8421 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2026-8421?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-8421, 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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