---
id: CVE-2026-70554
title: MaxSite CMS Unauthenticated PHP Object Injection via maxsite_comuser Cookie
summary: >-
  MaxSite CMS contains a PHP object injection vulnerability that allows
  unauthenticated attackers to execute arbitrary code by passing
  attacker-controlled serialized data in the maxsite_comuser cookie directly to
  unserialize() without vali…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-502
vendor: MaxSite
product: MaxSite CMS
affected:
  - cms >= 0.78 <= 109.5
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-08-05T13:52:48.956931Z'
published: '2026-08-04'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T14:18:36.342Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-70554'
references:
  - url: 'https://github.com/maxsite/cms'
    label: Product Repository
  - url: 'https://max-3000.com/page/maxsite-cms-109-6'
    label: Patch Commit
  - url: >-
      https://www.vulncheck.com/advisories/maxsite-cms-unauthenticated-php-object-injection-via-maxsite-comuser-cookie
tags:
  - cve.org
epss: 0.00851
epssPercentile: 0.56692
ingestedAt: '2026-09-24T15:45:56.716Z'
---

## Overview

MaxSite CMS contains a PHP object injection vulnerability that allows unauthenticated attackers to execute arbitrary code by passing attacker-controlled serialized data in the maxsite_comuser cookie directly to unserialize() without validation or class allowlisting. Attackers can craft a malicious serialized PHP object payload delivered in a single HTTP request to trigger magic methods during object graph reconstruction, enabling property-oriented programming attacks or remote code execution via available gadget chains such as those targeting SoapClient or Imagick extensions.

## Affected

- `cms >= 0.78 <= 109.5`

## Remediation

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