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

Quick assessment

Affected
Concrete CMS Concrete CMS
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Concrete CMS是Concrete CMS开源的一个面向团队的开源内容管理系统。 Concrete CMS 9.5.0及之前版本存在跨站请求伪造漏洞，该漏洞源于未验证CSRF令牌，可能导致攻击者覆盖包PHP文件并执行远程代码。

AI Predicted 7.5 Difficulty: Moderate EPSS 0.17% · P7

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
Concrete CMS Concrete CMS 5.0≤ 9.5.0 affected
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I. Basic Information for CVE-2026-8426

Vulnerability Information
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Vulnerability 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: CVE Program / CVE List V5
Vulnerability 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.   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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
跨站请求伪造(CSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
Concrete CMS 跨站请求伪造漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Concrete CMS是Concrete CMS开源的一个面向团队的开源内容管理系统。 Concrete CMS 9.5.0及之前版本存在跨站请求伪造漏洞，该漏洞源于未验证CSRF令牌，可能导致攻击者覆盖包PHP文件并执行远程代码。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Concrete CMS Concrete CMS 5.0 ~ 9.5.0 -

II. Public POCs for CVE-2026-8426

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III. Intelligence Information for CVE-2026-8426

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Vendor Pages for CVE-2026-8426 (1)

Same Patch Batch · Concrete CMS · 2026-05-21 · 41 CVEs total

CVE-2026-8240 Concrete CMS 9.5.0 and below is vulnerable to unauthenticated page metadata disclosure in
CVE-2026-8416 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8412 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8237 Concrete CMS 9.5.0 and below is vulnerable to IDOR in the`/ccm/frontend/conversations/mess
CVE-2026-8434 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8435 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8414 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8433 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8239 Concrete CMS 9.5.0 and below is vulnerable to IDOR in '/ccm/frontend/conversations/get_rat
CVE-2026-8411 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8432 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8236 Concrete CMS 9.5.0 and below is vulnerable to IDOR combined with a missing authentication
CVE-2026-8413 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8415 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8427 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete
CVE-2026-8238 Concrete CMS 9.5.0 and below is vulnerable to IDOR in '/ccm/frontend/conversations/message
CVE-2026-8245 Concrete CMS 9.5.0 and below is vulnerable to Reflected XSS in Legacy Pagination via HTML
CVE-2026-7890 Concrete CMS 9.5.0 is vulnerable to SSRF via RSS Displayer Block
CVE-2026-8139 Concrete CMS 9.5.0 and below is vulnerable to Stored XSS via external-link page cvName
CVE-2026-8409 Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Request Forgery (CSRF) at concrete

Showing top 20 of 41 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Concrete CMS
Same vendor: Concrete CMS
Same weakness: CWE-352

V. Comments for CVE-2026-8426

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