CVE-2026-18209: Software Security Vulnerability Vulnerability

LOW
Advisory Identifier: GHSA-c8xx-fr3x-6m5w
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CVSS 3.4
CWE-1288
Published
Advisory Summary

CVE-2026-18209 is a LOW (CVSS 3.4) security vulnerability vulnerability (CWE-1288: Improper Validation of Consistency within Input) affecting Software libraries in the Maven ecosystem. The weakness occurs when the product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent.. Remediation is available in the latest vendor maintenance releases.

CVE-2026-18209 at a Glance

CVE Identifier CVE-2026-18209
GHSA Identifier GHSA-c8xx-fr3x-6m5w
Severity LOW
CVSS v3.1 Base Score 3.4
CWE Classification CWE-1288: Improper Validation of Consistency within Input
Affected Product Software
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 3.4

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

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

How to Fix CVE-2026-18209

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-2026-18209, 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-1288: Improper Validation of Consistency within Input, where the product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent. 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

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

References

NVD — CVE-2026-18209 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-18209
access.redhat.com/errata/rhsa-2026:68... WEB
https://access.redhat.com/errata/RHSA-2026:68277
access.redhat.com/errata/rhsa-2026:68... WEB
https://access.redhat.com/errata/RHSA-2026:68278
Software Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-18209
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2508305

Frequently Asked Questions

What is CVE-2026-18209?
CVE-2026-18209 is a security vulnerability in Software classified as a security vulnerability vulnerability under CWE-1288: Improper Validation of Consistency within Input.
Which Software versions are affected?
Affected versions include releases prior to current release patches.
What version fixes CVE-2026-18209?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
What is the CVSS score of CVE-2026-18209?
CVE-2026-18209 has a CVSS v3.1 base score of 3.4 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N.
What CWE is associated with CVE-2026-18209?
CVE-2026-18209 is classified under CWE-1288: Improper Validation of Consistency within Input (The product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent.).
How can I check Maven dependencies for CVE-2026-18209?
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-c8xx-fr3x-6m5w",
  "modified" : "2026-09-16T18:31:19Z",
  "published" : "2026-07-31T09:31:18Z",
  "aliases" : [ "CVE-2026-18209" ],
  "details" : "A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-18209"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:68277"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:68278"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/security/cve/CVE-2026-18209"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2508305"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1288" ],
    "severity" : "LOW",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-07-31T08:16:27Z"
  }
}