NVD / CVE Program· CNA GitHub_M

CVE-2026-49400: October CMS: PHP Object Injection via Backend Widget Session Storage

Noroxi assessment

Priority: Monitor (action score 13/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.23% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. Administrator privileges are required. No user action is required. Special conditions such as timing or configuration are required.
Fixed version: october/system (Packagist) 4.2.23, 3.7.17.

Low priority for now. Upgrade to october/system (Packagist) 4.2.23, 3.7.17 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

LowCVSS 3.3 · v3.1—No exploit Fix available

Deserialization

Published: Sep 14, 2026
Updated: Sep 30, 2026
EPSS: 0.2% · 14th percentile
CWE: CWE-502

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 13 / 40 · 3.3 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 3.3; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Running WordPress? Scan your site free with WP Lens

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

octobercms october
- < 3.7.17, >= 4.0.0, < 4.2.23affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Packagist	october/system	from 4.0.0 · before 4.2.23	4.2.23
Packagist	october/system	before 3.7.17	3.7.17

Same product

octobercms: all records

Other highest-scoring records for the same primary product.

CVE-2021-32648Account Takeover in OctobercmsKEV
93Now
CVE-2017-1000119October CMS build 412 is vulnerable to PHP code execution in the file upload functionality resulting in site compromise and possibly other a
46Plan
CVE-2021-3311An issue was discovered in October through build 471.
40Plan

Published before and after this one in the same product

← EarlierCVE-2026-26274Apr 21, 2026 · October: Safe Mode Bypass via Twig Database Write Operations
26Monitor
← EarlierCVE-2026-27937Apr 21, 2026 · October: Reflected XSS via DataTable Form Widget
12Monitor
← EarlierCVE-2026-29179Apr 21, 2026 · October: Editor Sub-Permission Bypass for Asset and Blueprint File Operations
13Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Packagist:october/system	3.7.17	Package registry (OSV)
Packagist:october/system	4.2.23	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
Administrator privileges are required.
No user action is required.
Special conditions such as timing or configuration are required.

If successful

Confidentiality: low · data can be read
Integrity: low · data or configuration can be modified
Availability: none

Attack vector: Network
Attack complexity: High
Privileges required: High
User interaction: None
Scope: Unchanged
Confidentiality impact: Low
Integrity impact: Low
Availability impact: None

Weakness class (CWE)

CWE-502 · Deserialization of Untrusted Data

CVSS vector

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

nvd-secondary

Root cause

Data received over the network is deserialized into the language’s native object format without verifying its source. Code paths inside the object can be triggered during deserialization.

The bug in code

The whole CWE-502 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

python

1payload = sock.recv(65536)
2job = pickle.loads(payload)

Fixed

python

1payload = sock.recv(65536)
2if not hmac.compare_digest(sign(payload), header_sig):
3    raise PermissionError("invalid signature")
4job = JobSchema.validate(json.loads(payload))

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

Object InjectionCAPEC-586likelihood: Medium · High

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

For records you follow, these changes also arrive as notifications. →

References

github.com/octobercms/october/security/advisories/GHSA-2ff2-mx52-q8wp

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records