Concrete CMS 9.5.0 and below is vulnerable to CSRF on prepare_remote_upgrade() leading to one-request RCE via package overwrite_CVE-2026-8426

{
    "lastseen": "",
    "description": "Concrete CMS 9.5.0 and below does not validate a CSRF token before processing requests to /dashboard/extend/update/prepare_remote_upgrade/<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() method to execute in a single browser navigation. This results in remote code execution as the web server user.\u00a0\u00a0\u00a0In order to be vulnerable, the victim must be passing canInstallPackages,\u00a0victim 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.\u00a0The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of\u00a07.5 with vector\u00a0CVSS: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\u00a0https://github.com/maru1009\u00a0for reporting.",
    "published": "2026-05-21T20:22:09.950Z",
    "modified": "2026-05-21T20:22:09.950Z",
    "type": "cve",
    "title": "Concrete CMS 9.5.0 and below is vulnerable to CSRF on prepare_remote_upgrade() leading to one-request RCE via package overwrite",
    "source": "ConcreteCMS",
    "references": "https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes",
    "id": "CVE-2026-8426",
    "bulletinFamily": "",
    "cwe": [
        "CWE-352",
        "CWE-829"
    ],
    "cvelist": null,
    "sourceData": "Concrete CMS Concrete CMS 5.0",
    "sourceHref": "",
    "cvss": {
        "score": 7.5,
        "severity": "HIGH",
        "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",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
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        "baseScore": 0,
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        "privilegesRequired": "",
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        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
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            "baseScore": 0,
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    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "Concrete CMS",
    "version": "5.0",
    "vendor": "Concrete CMS",
    "ai_description": "",
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    "ai_score": 0
}