---
id: CVE-2026-49400
title: >-
  October System provides the system module for October Content Management
  System
summary: >-
  October System provides the system module for October Content Management
  System. Prior to versions 3.7.17 and 4.2.21, the backend `SessionMaker` trait
  stored widget session state as `base64(serialize(...))` and consumed it with
  `unserial…
severity: low
cvss: 3.3
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-502
vendor: octobercms
product: october
affected:
  - october < 3.7.17
  - 'october >= 4.0.0, < 4.2.23'
patched:
  - october/system 3.7.17
  - october/system 4.2.23
published: '2026-09-14'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T16:17:08.003'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-49400'
references:
  - url: >-
      https://github.com/octobercms/october/security/advisories/GHSA-2ff2-mx52-q8wp
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-2ff2-mx52-q8wp'
tags:
  - nvd
  - cve.org
  - ghsa
  - composer
epss: 0.00237
epssPercentile: 0.13138
aliases:
  - GHSA-2ff2-mx52-q8wp
ecosystem: composer
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-16T15:21:01.563061Z'
ingestedAt: '2026-09-14T17:11:16.570Z'
---

## Overview

October System provides the system module for October Content Management System. Prior to versions 3.7.17 and 4.2.21, the backend `SessionMaker` trait stored widget session state as `base64(serialize(...))` and consumed it with `unserialize()` without an `allowed_classes` restriction. Any code path that could write to a `widget.*` session key with attacker-controlled bytes could trigger PHP object injection the next time the widget read its session state, allowing instantiation of arbitrary classes and reachable PHP gadget chains. This issue only affects installations running with `cms.safe_mode` enabled. Safe Mode is a niche opt-in feature, primarily used for demo installations and multi-tenant or shared-editor scenarios where untrusted users are deliberately granted access to the CMS markup editor. In standard production deployments Safe Mode is off, backend access is restricted to trusted administrators, and a markup editor can already execute arbitrary PHP directly. The session-write path that reaches this sink is gated by the Safe Mode sandbox, so installations without Safe Mode enabled are not exposed. Scope of impact is narrow even with Safe Mode enabled. The standard backend code paths that populate widget session state (search terms, sort options, selected IDs, filter values) wrap the input inside a known array shape before serializing, so user-supplied values never reach `unserialize()` as a controllable serialized payload. Exploitation requires the Safe Mode session-write path together with a suitable PHP gadget chain reachable from the installed dependency set. The hardening below removes the underlying object-injection sink so the class of issue is closed off regardless. The vulnerability has been patched in v3.7.17 and v4.2.21. Two changes were applied. `Backend\Traits\SessionMaker` now stores widget session state as plain JSON instead of `base64(serialize(...))`, eliminating the object-injection sink entirely for new writes. Reads transparently fall back to the legacy format for one upgrade cycle so existing sessions retain their saved widget state. The legacy `unserialize()` fallback path now sets `allowed_classes => false`, so even values written before the upgrade cannot instantiate objects. As a workaround, restrict CMS markup editing access to fully trusted administrators only, the standard October CMS recommendation for any deployment.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-49400)

Affected packages:

- `october/system < 3.7.17`
- `october/system >= 4.0.0, < 4.2.23`

Patched in:

- `october/system 3.7.17`
- `october/system 4.2.23`

Source: https://github.com/advisories/GHSA-2ff2-mx52-q8wp