What’s Vulnerable › Vulnerabilities

CVE-2026-70554: MaxSite CMS Unauthenticated PHP Object Injection via maxsite_comuser Cookie

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-04 · updated 2026-10-24
• Weakness: CWE-502

Description

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 products

• MaxSite CMS: from 0.78 through 109.5

References

• https://github.com/maxsite/cms
• https://max-3000.com/page/maxsite-cms-109-6
• https://www.vulncheck.com/advisories/maxsite-cms-unauthenticated-php-object-injection-via-maxsite-comuser-cookie

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