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Concrete CMS EUVD-2026-34164

| CVE-2026-7888 HIGH
Deserialization of Untrusted Data (CWE-502)
2026-06-03 ConcreteCMS GHSA-52pr-7vmf-2w7x
PHP Deserialization
8.4
CVSS 4.0 · NVD
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Severity by source

NVD PRIMARY
8.4 HIGH
CVSS:4.0/AV:L/AC:L/AT:N/PR:H/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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:4.0/AV:L/AC:L/AT:N/PR:H/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
Local
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
X

Lifecycle Timeline

4
Analysis Generated
Jun 03, 2026 - 21:20 vuln.today
Patch available
Jun 03, 2026 - 20:01 EUVD
CVSS changed
Jun 03, 2026 - 19:22 NVD
8.4 (HIGH)
CVE Published
Jun 03, 2026 - 18:10 nvd
UNKNOWN (no severity yet)

DescriptionCVE.org

Concrete CMS below 9.5.2 is vulnerable to PHP Object Injection via unserialize() calls in the Workflow, Form block, and File/Set components that lack the allowed_classes restriction. An unauthenticated attacker may trigger arbitrary PHP object instantiation if a malicious serialized payload has been placed in the database. Thanks XananasX7 and Sanjorn Keeratirungsan (dizconnect) for both independently reporting. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 8.4 with vector CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N.

AnalysisAI

PHP object injection in Concrete CMS versions below 9.5.2 allows authenticated high-privileged attackers to trigger arbitrary PHP object instantiation through unsafe unserialize() calls in the Workflow, Form block, and File/Set components. The vulnerability requires a malicious serialized payload to be placed in the database beforehand, and no public exploit identified at time of analysis. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Obtain privileged CMS account or chained injection
Delivery
Write malicious serialized payload to Workflow/Form/File-Set DB row
Exploit
Trigger component that loads the row
Execution
Unrestricted unserialize() instantiates attacker class
Persist
POP gadget chain executes during magic methods
Impact
Arbitrary PHP code runs in web server context
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Vulnerability AssessmentAI

Exploitation Exploitation requires (1) the attacker to have a means of writing a crafted serialized payload into the Concrete CMS database - typically high-privilege editorial/admin access (PR:H in the vector) or a chained injection vulnerability - and (2) the vulnerable site to use the Workflow component, Form block, or File/Set component that subsequently deserializes that database value. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 vector AV:L/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H paints a mixed picture: local attack vector and high privileges required substantially limit reach, but full confidentiality, integrity, and availability impact on the vulnerable component justify the 8.4 score. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker first uses a separate primitive - for example a compromised editor account or a stored injection bug - to write a crafted serialized PHP object string into a Workflow, Form block, or File/Set database row. When the application subsequently retrieves and deserializes that row via the unrestricted unserialize() call, PHP instantiates the attacker-chosen class and fires its magic methods, executing a POP gadget chain that yields arbitrary code execution in the web server context. …
Remediation Vendor-released patch: upgrade to Concrete CMS 9.5.2 or later, which adds the allowed_classes restriction to the affected unserialize() call sites; release notes are at https://documentation.concretecms.org/9-x/developers/introduction/version-history/952-release-notes. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

24 hours: Inventory all Concrete CMS deployments and identify versions below 9.5.2; restrict administrative access to workflow, form block, and file/set management to essential personnel only. …

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EUVD-2026-34164 vulnerability details – vuln.today
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