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MaxSite CMS EUVDEUVD-2026-52894

| CVE-2026-70554 CRITICAL
Deserialization of Untrusted Data (CWE-502)
2026-08-04 VulnCheck GHSA-jm66-348j-qvv2
RCE PHP Deserialization Maxsite Cms
9.3
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
9.8 CRITICAL

Unauthenticated single-request cookie injection to unserialize() gives network vector, low complexity, no privileges or interaction; RCE via gadget yields full C/I/A impact within the vulnerable component.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

2
Analysis Generated
Aug 04, 2026 - 21:00 vuln.today
CVE Published
Aug 04, 2026 - 20:11 cve.org
CRITICAL 9.3

DescriptionCVE.org

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.

AnalysisAI

Unauthenticated remote code execution in MaxSite CMS is possible because the application passes attacker-controlled serialized data from the maxsite_comuser cookie directly into PHP's unserialize() without validation or class allowlisting. Any remote attacker can send a single crafted HTTP request carrying a malicious serialized PHP object to trigger property-oriented programming (POP) gadget chains and execute arbitrary code. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Set malicious payload in maxsite_comuser cookie
Delivery
Send single unauthenticated HTTP request
Exploit
Cookie value reaches unserialize() sink
Execution
Object graph triggers magic methods
Persist
POP gadget chain (SoapClient/Imagick) executes
Impact
Arbitrary code execution on server
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Vulnerability AssessmentAI

Exploitation The exact prerequisite is that the target processes the client-supplied maxsite_comuser cookie by passing its value to PHP unserialize() without class allowlisting - this is the default code path in vulnerable MaxSite CMS versions, so no non-default configuration is needed to reach the sink (AV:N/AC:L/PR:N/UI:N, unauthenticated, no user interaction). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment This is a genuine high-priority issue, not an inflated high-CVSS artifact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker crafts a malicious serialized PHP object payload built around a known gadget chain (for example a SoapClient- or Imagick-based POP chain) and sends it as the value of the maxsite_comuser cookie in a single unauthenticated HTTP request to any MaxSite CMS page that processes that cookie. When the application calls unserialize() on the cookie, the object graph is reconstructed and magic methods fire, driving the gadget chain to execute attacker-controlled code or perform server-side request forgery. …
Remediation Vendor-released patch: upgrade to MaxSite CMS 109.6 or later, per the vendor advisory at https://max-3000.com/page/maxsite-cms-109-6; source and releases are available at https://github.com/maxsite/cms and the vulnerability details at https://www.vulncheck.com/advisories/maxsite-cms-unauthenticated-php-object-injection-via-maxsite-comuser-cookie. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, inventory all MaxSite CMS deployments, identify internet-facing systems, and document current version numbers. …

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EUVD-2026-52894 vulnerability details – vuln.today
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