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CVE-2026-8135— Concrete CMS 9.5.0 and below is vulnerable to RCE due to insecure deserialization occurring in the ExpressEntryList block controller.

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及之前版本存在代码问题漏洞，该漏洞源于ExpressEntryList块控制器中存在不安全的反序列化，可能导致具有添加块权限的恶意管理员通过利用REST API功能绕过保护机制，注入恶意序列化有效载荷，最终导致远程代码执行。

AI Predicted 8.8 Difficulty: Easy EPSS 0.47% · P39

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-2026-8135

Vulnerability Information
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Vulnerability Title
Concrete CMS 9.5.0 and below is vulnerable to RCE due to insecure deserialization occurring in the ExpressEntryList block controller.
Source: CVE Program / CVE List V5
Vulnerability Description
Concrete CMS 9.5.0 and below is vulnerable to Remote Code Execution due to insecure deserialization occurring in the ExpressEntryList block controller. An rogue administrator with privileges to add blocks to an area can bypass the intended protection mechanism (_fromCIF === true), which normally restricts malicious inputs over form POST requests, by leveraging the REST API functionality. Because the REST API parses requests using json_decode(), the string "true" is evaluated as a strict PHP Boolean(true).  This bypass allows the attacker to inject a malicious serialized payload  into the block's filterFields database column. The payload will subsequently be executed when the block's data is viewed or edited by an administrator leading to complete server takeover (RCE).The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 8.9 with a vector of CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H.  Thanks Nguyễn Văn Thiện https://github.com/Thien225409  for reporting
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
Source: CVE Program / CVE List V5
Vulnerability Type
可信数据的反序列化
Source: CVE Program / CVE List V5
Vulnerability Title
Concrete CMS 代码问题漏洞
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及之前版本存在代码问题漏洞，该漏洞源于ExpressEntryList块控制器中存在不安全的反序列化，可能导致具有添加块权限的恶意管理员通过利用REST API功能绕过保护机制，注入恶意序列化有效载荷，最终导致远程代码执行。
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-2026-8135

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III. Intelligence Information for CVE-2026-8135

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Vendor Pages for CVE-2026-8135 (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 → →

IV. Related Vulnerabilities

Same product: Concrete CMS
Same vendor: Concrete CMS
Same weakness: CWE-502

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