CVE-2026-8426

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 does not validate a CSRF token before processing requests to /dashboard/extend/update/prepare_remote_upgrade/. An attacker who controls the remote package returned for a known marketplace item ID can overwrite the package PHP on disk and force its upgrade() method to execute in a single browser navigation. This results in remote code execution as the web server user.   In order to be vulnerable, the victim must be passing canInstallPackages, victim site must be connected to the Concrete marketplace; and the attacker controls the package returned for a marketplace item ID already installed on the victim site. 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 2, 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-2026-8426(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(2)

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

Data Freshness Timeline

(refreshed 9× in last 7d / 64× 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 133 total refreshes for this CVE.

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

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-8426?
CVE-2026-8426 is a high vulnerability published on May 21, 2026. Concrete CMS 9.5.0 and below does not validate a CSRF token before processing requests to /dashboard/extend/update/prepareremoteupgrade/<remoteMPID>. An attacker who controls the remote package returned for a known marketplace item ID can overwrite the package PHP on disk and force its upgrade()…
When was CVE-2026-8426 disclosed?
CVE-2026-8426 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-2026-8426 actively exploited?
CVE-2026-8426 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-2026-8426?
CVE-2026-8426 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2026-8426?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-8426, 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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