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CVE-2026-18426— Concrete CMS 9.0.0 to 9.5.2 Express Form block missing authorization allows an authenticated editor to modify Express Forms they cannot edit

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 版本 9.0.0 至 9.5.2 未对 Express Form 区块的控制管理操作执行区块级别的编辑权限检查，这些操作仅依赖 CSRF 令牌验证。由于令牌与用户和具体操作绑定，而非与特定区块、页面或表单绑定，因此拥有单个 Express Form 编辑权限的已认证用户，可以复用有效获取的令牌，对其无编辑权限的 Express Form 中的控件执行添加、修改或删除操作，甚至通过注入一个其值后续作为 HTML 渲染的控件来实现存储型跨站脚本攻击（Stored XSS）。 Concrete

CVSS 2.0 · Low
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I. Basic Information for CVE-2026-18426

Vulnerability Information
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Vulnerability Title
Concrete CMS 9.0.0 to 9.5.2 Express Form block missing authorization allows an authenticated editor to modify Express Forms they cannot edit
Source: CVE Program / CVE List V5
Vulnerability Description
Concrete CMS 9.0.0 through 9.5.2 did not enforce a block-level edit-permission check on the Express Form block's control-management actions, which relied solely on CSRF token validation. Because the token is bound to the user and action rather than to a specific block, page, or form, an authenticated user with edit access to one Express Form could reuse a validly obtained token to add, modify, or delete controls on Express Forms they were not authorized to edit, including injecting a control whose value is later rendered as HTML to achieve stored XSS. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.0 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks Yat Wu for reporting.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Concrete CMS Concrete CMS 9.0.0 ~ 9.5.2 -

II. Public POCs for CVE-2026-18426

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III. Intelligence Information for CVE-2026-18426

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Vendor Pages for CVE-2026-18426 (1)

Same Patch Batch · Concrete CMS · 2026-09-15 · 31 CVEs total

CVE-2026-18110 8.7 HIGH Concrete CMS 9.0.0 through 9.5.2 is vulnerable to missing authorization in the user select
CVE-2026-81894 8.5 HIGH Concrete CMS 9.5.2 and below is vulnerable to Stored DOM-based Cross-site Scripting (XSS)
CVE-2026-18111 8.5 HIGH Concrete CMS below 9.5.4 allows privilege escalation because adding users and assigning gr
CVE-2026-81895 8.5 HIGH Concrete CMS 9.5.2 and below is vulnerable to Stored SQL Injection in Concrete CMS Documen
CVE-2026-81896 8.4 HIGH Concrete CMS below version 9.5.3 is vulnerable to Stored XSS in Concrete CMS Form Submissi
CVE-2026-81897 7.7 HIGH Concrete CMS below version 9.5.3 is vulnerable to Stored XSS via Express form Text control
CVE-2026-81898 7.5 HIGH Concrete CMS below version 9.5.3 is vulnerable to Stored XSS via country-less Address att
CVE-2026-18113 7.5 HIGH Concrete CMS 9.0 to 9.5.2 is vulnerable to Stored XSS in the Top Navigation Bar Block via
CVE-2026-18115 7.4 HIGH In Concrete CMS 9.2.0 to 9.5.2, Missing Authorization in REST API Users update() and chang
CVE-2026-81899 7.3 HIGH Concrete CMS 9.0 to 9.5.2 is vulnerable to Stored XSS via group folder name on the Members
CVE-2026-68533 2.3 LOW Missing Authorization in Concrete CMS versions below 9.5.3 Conversation File Upload Allows
CVE-2026-81921 2.3 LOW In Concrete CMS 8.5.3 to 9,5,2, OAuth 2.0 Refresh-Token Grant Bypasses Account Status
CVE-2026-81920 2.3 LOW Concrete CMS below 9.5.3 is vulnerable to Cross-Site Request Forgery (CSRF) in Dashboard S
CVE-2026-68532 2.3 LOW Concrete CMS 9.0.0 to 9.5.2 is vunerable to CSRF in Concrete CMS Group Type Deletion Dashb
CVE-2026-68534 2.3 LOW Concrete CMS below 9.5.2 is vulnerable to Stored XSS via unescaped Express entry labels in
CVE-2026-81919 2.3 LOW Concrete CMS below 9.5.3 is vulnerable to Cross-Site Request Forgery (CSRF) in Block Arran
CVE-2026-81922 2.1 LOW "In Concrete CMS below 9.5.3, there is Missing authorization in the sitemap page reorder a
CVE-2026-81925 2.1 LOW Concrete CMS below 9.5.3 is vulnerable to Reflected Cross-Site Scripting (XSS) via Convers
CVE-2026-18424 2.1 LOW Concrete CMS 9.0.0 to 9.5.2 is vulnerable to SSRF protection bypass in remote file import
CVE-2026-18425 2.1 LOW IDOR in Concrete CMS 9.0.0 through 9.5.2 dashboard sitemap reorder (SitemapUpdate::updateD

Showing top 20 of 31 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Concrete CMS
Same vendor: Concrete CMS
Same weakness: CWE-862

V. Comments for CVE-2026-18426

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