CVE-2026-18426: Software Security Vulnerability Vulnerability

LOW
Advisory Identifier: GHSA-g5mv-jcqh-ch66
Share
CVSS 6.5
CWE-862
Published
Advisory Summary

CVE-2026-18426 is a LOW (CVSS 6.5) security vulnerability vulnerability (CWE-862: Missing Authorization) affecting Software libraries in the Maven ecosystem. The weakness occurs when the product does not perform an authorization check when an actor attempts to access a resource or perform an action.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-18426 at a Glance

CVE Identifier CVE-2026-18426
GHSA Identifier GHSA-g5mv-jcqh-ch66
Severity LOW
CVSS v3.1 Base Score 6.5
CWE Classification CWE-862: Missing Authorization
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-18426

To remediate this vulnerability, upgrade all affected Software dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-18426, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree

Analyze the terminal output to locate any version of Software in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The mvn dependency:tree command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-862: Missing Authorization, where the product does not perform an authorization check when an actor attempts to access a resource or perform an action. In Software, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

References

NVD — CVE-2026-18426 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-18426
documentation.concretecms.org/developers/introduc... WEB
https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes

Frequently Asked Questions

What is CVE-2026-18426?
CVE-2026-18426 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-862: Missing Authorization.
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-18426?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What is the CVSS score of CVE-2026-18426?
CVE-2026-18426 has a CVSS v3.1 base score of 6.5 (LOW) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2026-18426?
CVE-2026-18426 is classified under CWE-862: Missing Authorization (The product does not perform an authorization check when an actor attempts to access a resource or perform an action.).
How can I check Maven dependencies for CVE-2026-18426?
Run the dependency tree command: 'mvn dependency:tree'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g5mv-jcqh-ch66",
  "modified" : "2026-09-21T18:31:51Z",
  "published" : "2026-09-15T21:33:03Z",
  "aliases" : [ "CVE-2026-18426" ],
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-18426"
  }, {
    "type" : "WEB",
    "url" : "https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-862" ],
    "severity" : "LOW",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-09-15T21:16:36Z"
  }
}