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CVE-2026-8421— Concrete CMS 9.5.0 and below is vulnerable to CSRF on install_package() with conditional token bypass leading to RCE

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install_package()方法存在CSRF漏洞，可能导致攻击者强制安装包并执行远程代码。

AI Predicted 9.1 Difficulty: Easy EPSS 0.17% · P7

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-2026-8421

Vulnerability Information
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Vulnerability Title
Concrete CMS 9.5.0 and below is vulnerable to CSRF on install_package() with conditional token bypass leading to RCE
Source: CVE Program / CVE List V5
Vulnerability Description
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/<handle>/, 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.
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install_package()方法存在CSRF漏洞，可能导致攻击者强制安装包并执行远程代码。
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-2026-8421

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III. Intelligence Information for CVE-2026-8421

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Vendor Pages for CVE-2026-8421 (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-2026-8421

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