Vulnerability-Lookup

GHSA-2FF2-MX52-Q8WP

Vulnerability from github – Published: 2026-09-14 17:08 – Updated: 2026-09-14 17:08

Summary

October CMS: PHP Object Injection via Backend Widget Session Storage

Details

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.

Impact

Arbitrary PHP code execution as the web server user, via a gadget chain deserialized from a widget session key, triggered the next time the affected widget is rendered
Requires cms.safe_mode to be enabled, and a backend user with CMS markup editing access who is not intended to be trusted as a full administrator
A suitable PHP gadget chain must be reachable from the installed dependency set
Not exploitable when Safe Mode is disabled

Patches

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.

Workarounds

If upgrading immediately is not possible, restrict CMS markup editing access to fully trusted administrators only, the standard October CMS recommendation for any deployment.

References

Reported by EndlssNightmare

Severity

3.3 (Low)


                  
                    CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "october/system"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.7.17"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "october/system"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.2.23"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49400"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-502"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-14T17:08:06Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "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.\n\n**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.\n\n**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.\n\n### Impact\n- Arbitrary PHP code execution as the web server user, via a gadget chain deserialized from a widget session key, triggered the next time the affected widget is rendered\n- Requires `cms.safe_mode` to be enabled, and a backend user with CMS markup editing access who is not intended to be trusted as a full administrator\n- A suitable PHP gadget chain must be reachable from the installed dependency set\n- Not exploitable when Safe Mode is disabled\n\n### Patches\nThe vulnerability has been patched in v3.7.17 and v4.2.21. Two changes were applied:\n\n- `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.\n- The legacy `unserialize()` fallback path now sets `allowed_classes =\u003e false`, so even values written before the upgrade cannot instantiate objects.\n\n### Workarounds\nIf upgrading immediately is not possible, restrict CMS markup editing access to fully trusted administrators only, the standard October CMS recommendation for any deployment.\n\n### References\n- Reported by EndlssNightmare",
  "id": "GHSA-2ff2-mx52-q8wp",
  "modified": "2026-09-14T17:08:06Z",
  "published": "2026-09-14T17:08:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/octobercms/october/security/advisories/GHSA-2ff2-mx52-q8wp"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/octobercms/october"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "October CMS: PHP Object Injection via Backend Widget Session Storage"
}

CVE-2026-49400 (GCVE-0-2026-49400)

Vulnerability from cvelistv5 – Published: 2026-09-14 17:15 – Updated: 2026-09-16 15:21

Title

October CMS: PHP Object Injection via Backend Widget Session Storage

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 `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.

Severity

3.3 (Low)


                        
                          CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-16 15:21 UTC

CWE

CWE-502 - Deserialization of Untrusted Data

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/octobercms/october/security/ad…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
octobercms	october	Affected: < 3.7.17 Affected: >= 4.0.0, < 4.2.23

Show details on NVD website

JSON

To clipboard

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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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Action not permitted

GHSA-2FF2-MX52-Q8WP

Impact

Patches

Workarounds

References

CVE-2026-49400 (GCVE-0-2026-49400)

Tags

Sightings

Nomenclature

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