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
8.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.8Exploit: None knownExposed: 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)
EG Risk
40(Track)
EG Risk 40/100SSVC: 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
Severity88% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
7%
KEV
Not listed

Published

May 21, 2026

Last Modified

July 23, 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 11× in last 7d / 41× 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 120 total refreshes for this CVE.

  1. 2026-08-02 04:45 UTCEG score recompute
  2. 2026-08-02 02:27 UTCEPSS rescore
  3. 2026-08-01 17:23 UTCEG score recompute
  4. 2026-08-01 04:16 UTCEPSS rescore
  5. 2026-07-30 16:28 UTCEPSS rescore
  6. 2026-07-30 01:30 UTCEPSS rescore
  7. 2026-07-29 17:40 UTCEG score recompute
  8. 2026-07-28 15:37 UTCEPSS rescore
  9. 2026-07-27 14:14 UTCEPSS rescore
  10. 2026-07-26 14:54 UTCEPSS rescore
  11. 2026-07-26 08:08 UTCEG score recompute
  12. 2026-07-25 14:18 UTCEPSS rescore
  13. 2026-07-24 14:18 UTCEPSS rescore
  14. 2026-07-23 14:18 UTCEPSS rescore
  15. 2026-07-23 03:23 UTCEG score recompute
  16. 2026-07-22 14:08 UTCEPSS rescore
  17. 2026-07-21 15:25 UTCEPSS rescore
  18. 2026-07-21 15:25 UTCEPSS rescore
  19. 2026-07-20 17:08 UTCEPSS rescore
  20. 2026-07-19 14:31 UTCEPSS rescore
  21. 2026-07-19 02:29 UTCEPSS rescore
  22. 2026-07-18 10:04 UTCEPSS rescore
  23. 2026-07-17 21:59 UTCOSV refresh
  24. 2026-07-16 17:03 UTCEPSS rescore
  25. 2026-07-15 16:57 UTCEPSS rescore
Show 75 more
  1. 2026-07-15 02:00 UTCEPSS rescore
  2. 2026-07-13 22:31 UTCEPSS rescore
  3. 2026-07-13 06:13 UTCEPSS rescore
  4. 2026-07-11 08:27 UTCEPSS rescore
  5. 2026-07-09 19:10 UTCEPSS rescore
  6. 2026-07-08 15:16 UTCEPSS rescore
  7. 2026-07-07 13:46 UTCEPSS rescore
  8. 2026-07-07 13:46 UTCEPSS rescore
  9. 2026-07-06 16:27 UTCEPSS rescore
  10. 2026-07-06 16:27 UTCEPSS rescore
  11. 2026-07-06 02:23 UTCEPSS rescore
  12. 2026-07-06 02:23 UTCEPSS rescore
  13. 2026-07-05 02:31 UTCEPSS rescore
  14. 2026-07-05 02:30 UTCEPSS rescore
  15. 2026-07-04 06:31 UTCEPSS rescore
  16. 2026-07-04 06:31 UTCEPSS rescore
  17. 2026-07-01 15:07 UTCEPSS rescore
  18. 2026-06-30 23:22 UTCEPSS rescore
  19. 2026-06-29 14:06 UTCEPSS rescore
  20. 2026-06-28 14:07 UTCEPSS rescore
  21. 2026-06-28 04:56 UTCEPSS rescore
  22. 2026-06-27 03:08 UTCEPSS rescore
  23. 2026-06-25 13:50 UTCEPSS rescore
  24. 2026-06-24 14:05 UTCEPSS rescore
  25. 2026-06-23 21:33 UTCEPSS rescore
  26. 2026-06-22 14:25 UTCEPSS rescore
  27. 2026-06-21 14:56 UTCEPSS rescore
  28. 2026-06-21 01:59 UTCEPSS rescore
  29. 2026-06-19 19:26 UTCEPSS rescore
  30. 2026-06-18 17:52 UTCEPSS rescore
  31. 2026-06-17 22:39 UTCGHSA enrichment
  32. 2026-06-17 17:53 UTCEPSS rescore
  33. 2026-06-17 11:07 UTCGHSA enrichment
  34. 2026-06-16 19:42 UTCGHSA enrichment
  35. 2026-06-16 17:53 UTCEPSS rescore
  36. 2026-06-16 02:59 UTCGHSA enrichment
  37. 2026-06-15 17:49 UTCEPSS rescore
  38. 2026-06-15 17:49 UTCEPSS rescore
  39. 2026-06-15 15:37 UTCGHSA enrichment
  40. 2026-06-15 00:57 UTCGHSA enrichment
  41. 2026-06-14 23:18 UTCEPSS rescore
  42. 2026-06-14 13:34 UTCGHSA enrichment
  43. 2026-06-14 02:12 UTCGHSA enrichment
  44. 2026-06-13 23:00 UTCEPSS rescore
  45. 2026-06-13 14:51 UTCGHSA enrichment
  46. 2026-06-13 03:29 UTCGHSA enrichment
  47. 2026-06-12 23:12 UTCEPSS rescore
  48. 2026-06-12 23:12 UTCEPSS rescore
  49. 2026-06-12 15:40 UTCGHSA enrichment
  50. 2026-06-12 04:06 UTCGHSA enrichment
  51. 2026-06-11 16:44 UTCGHSA enrichment
  52. 2026-06-11 14:00 UTCEPSS rescore
  53. 2026-06-11 04:07 UTCGHSA enrichment
  54. 2026-06-10 22:19 UTCEPSS rescore
  55. 2026-06-10 16:46 UTCGHSA enrichment
  56. 2026-06-10 13:22 UTCEPSS rescore
  57. 2026-06-10 05:25 UTCGHSA enrichment
  58. 2026-06-09 18:04 UTCGHSA enrichment
  59. 2026-06-09 06:43 UTCGHSA enrichment
  60. 2026-06-08 19:21 UTCGHSA enrichment
  61. 2026-06-08 14:17 UTCEPSS rescore
  62. 2026-06-08 04:54 UTCGHSA enrichment
  63. 2026-06-07 17:33 UTCGHSA enrichment
  64. 2026-06-07 15:25 UTCEPSS rescore
  65. 2026-06-07 06:12 UTCGHSA enrichment
  66. 2026-06-06 18:51 UTCGHSA enrichment
  67. 2026-06-06 13:47 UTCEPSS rescore
  68. 2026-06-06 07:30 UTCGHSA enrichment
  69. 2026-06-05 22:47 UTCEPSS rescore
  70. 2026-06-05 20:08 UTCGHSA enrichment
  71. 2026-06-05 08:47 UTCGHSA enrichment
  72. 2026-06-05 06:10 UTCEPSS rescore
  73. 2026-06-04 21:26 UTCGHSA enrichment
  74. 2026-06-04 13:12 UTCEPSS rescore
  75. 2026-06-04 10:05 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 July 23, 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 0% probability of exploitation in the next 30 days, which ranks it in the top 93.3% of all scored CVEs.
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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