CVE-2026-27937: October CMS Cross-Site Scripting Vulnerability

LOW
Advisory Identifier: GHSA-jj38-h5w5-mvpf
Share
CVSS 3.1
CWE-79
Published
Advisory Summary

CVE-2026-27937 is a LOW (CVSS 3.1) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting October CMS libraries in the Packagist ecosystem. The issue involves reflected xss via datatable form widget. Remediation is available by upgrading affected packages to version 3.7.16.

CVE-2026-27937 at a Glance

CVE Identifier CVE-2026-27937
GHSA Identifier GHSA-jj38-h5w5-mvpf
Severity LOW
CVSS v3.1 Base Score 3.1
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product October CMS
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 3.1

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:U/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 Unchanged (S:U)
Confidentiality None (C:N)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-27937

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

october/system fixed: 3.7.16 
Upgrade october/system to 3.7.16
october/system fixed: Latest secure release 
Upgrade october/system to Latest secure release
Verify Direct and Transitive Dependencies

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

inspect dependencies for october/system

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-27937, inspect your project dependencies for October CMS:

inspect dependencies for october/system

Analyze the terminal output to locate any version of October CMS in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.7.16), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In October CMS, 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 reflected Cross-Site Scripting (XSS) vulnerability was identified in the backend DataTable widget where a query parameter was rendered without proper output escaping. ### Impact - Reflected XSS only, no stored/persistent component - The backend URL prefix is customizable and must be known or guessed by the attacker - Requires an authenticated backend user to visit a crafted URL - No direct access is gained without social engineering ### Patches The vulnerability has been patched in v3.7.16 and v4.1.16. The affected parameter is now properly escaped. All users are encouraged to upgrade to the latest patched version. ### Workarounds - Use a non-default backend URL prefix (recommended as standard practice) - Implement a Content Security Policy (CSP) for backend pages

CVE-2026-27937 Affected October CMS Versions

2 component(s)
Fixed Versions:
3.7.16
Product / Package Ecosystem Affected Versions Fixed Version
october/system
 Packagist
< 3.7.16
3.7.16
october/system
 Packagist
≥ 4.0.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/octobercms/october/security/advisories/GHSA-jj38-h5w5-mvpf
NVD — CVE-2026-27937 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27937
October CMS Source Repository REPOSITORY
https://github.com/octobercms/october

Frequently Asked Questions

What is CVE-2026-27937?
CVE-2026-27937 is a security vulnerability in October CMS involving Reflected XSS via DataTable Form Widget under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which October CMS versions are affected?
Affected versions include releases prior to 3.7.16 across affected packages: october/system.
What version fixes CVE-2026-27937?
Upgrading to 3.7.16 (or the latest patched release for your respective branch) resolves the vulnerability.
Is october/system affected?
Yes, october/system is affected in releases prior to 3.7.16, Latest secure release. Upgrade your dependency to 3.7.16, Latest secure release or later.
What is the CVSS score of CVE-2026-27937?
CVE-2026-27937 has a CVSS v3.1 base score of 3.1 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-27937?
CVE-2026-27937 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Packagist dependencies for CVE-2026-27937?
Run the dependency tree command: 'inspect dependencies for october/system'. 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-jj38-h5w5-mvpf",
  "modified" : "2026-04-24T21:06:33Z",
  "published" : "2026-04-21T17:15:21Z",
  "aliases" : [ "CVE-2026-27937" ],
  "summary" : "October CMS: Reflected XSS via DataTable Form Widget",
  "details" : "A reflected Cross-Site Scripting (XSS) vulnerability was identified in the backend DataTable widget where a query parameter was rendered without proper output escaping.\n\n### Impact\n- Reflected XSS only, no stored/persistent component\n- The backend URL prefix is customizable and must be known or guessed by the attacker\n- Requires an authenticated backend user to visit a crafted URL\n- No direct access is gained without social engineering\n\n### Patches\nThe vulnerability has been patched in v3.7.16 and v4.1.16. The affected parameter is now properly escaped. All users are encouraged to upgrade to the latest patched version.\n\n### Workarounds\n- Use a non-default backend URL prefix (recommended as standard practice)\n- Implement a Content Security Policy (CSP) for backend pages",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "october/system"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.7.16"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "october/system"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 4.1.16"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/octobercms/october/security/advisories/GHSA-jj38-h5w5-mvpf"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27937"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/octobercms/october"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-21T17:15:21Z",
    "nvd_published_at" : "2026-04-21T17:16:35Z"
  }
}