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Windsor Theme EUVDEUVD-2026-96517

| CVE-2026-66563 CRITICAL
Deserialization of Untrusted Data (CWE-502)
2026-10-10 Patchstack GHSA-vfx8-984f-hxhg
9.8
CVSS 3.1 · Vendor: Patchstack
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Send crafted request to theme endpoint
  2. Delivery
    Deliver malicious serialized PHP object
  3. Exploit
    Trigger unserialize() object injection
  4. Execution
    Invoke gadget chain in loaded code
  5. Impact
    Execute attacker actions as web user

Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A08:2025 - Software or Data Integrity Failures
ASVS 5.0
V1 - Encoding and Sanitization Safe deserialization, type allowlists
MITRE ATT&CK

2 techniques across 2 tactics: Execution, Initial Access

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Exploitation Conditions

Exploitation requires the attacker to reach a Windsor theme code path (version <= 2.10) that passes attacker-supplied input into PHP unserialize(), which per the CVSS vector needs no authentication (PR:N) and no user interaction (UI:N) against a default install. The decisive limiting factor is that PHP Object Injection yields real impact (RCE, file or data operations) only when a usable 'gadget' chain of magic methods exists in the theme, WordPress core, or an installed plugin; without a reachable gadget chain the injection may be inert or limited. Realistic risk is therefore bounded by the specific plugin/theme/core combination deployed on the target site rather than by the theme alone.

Impact

The input CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, base 9.8) describes a fully network-reachable, unauthenticated, low-complexity flaw with total confidentiality, integrity, and availability impact - the maximal-severity profile for an application-layer bug, consistent with CWE-502 (deserialization) leading to PHP Object Injection. No EPSS score, no KEV listing, and no POC indicator were provided in the intelligence set, so exploitation likelihood cannot be quantified: there is no public exploit identified at time of analysis and no confirmation of active exploitation. An important caveat tempers the raw score: PHP Object Injection is only directly weaponizable into code execution, file operations, or data theft when a usable gadget chain exists in the theme, WordPress core, or co-installed plugins - the AC:L rating assumes such a chain is readily reachable, which is not independently confirmed here. The single source is Patchstack, a reputable WordPress-vulnerability vendor, which lends credibility to the finding itself but the absence of any corroborating vendor (ThemeREX) advisory, EPSS, or exploitation signal means this is currently a high-potential-severity issue without evidence of real-world weaponization. Treat as a patch-priority for any site running the Windsor theme, but recognize the real-world exploited-risk signal is presently unproven rather than confirmed.

Exploit ScenarioDerived

A remote, unauthenticated attacker sends a crafted HTTP request to a vulnerable endpoint of the Windsor theme (<= 2.10) containing an attacker-controlled serialized PHP object, which the theme passes to unserialize(). If a suitable gadget chain is present in the theme, WordPress core, or an installed plugin, the injected object triggers that chain on instantiation/destruction, enabling actions such as arbitrary file write, SQL manipulation, or remote code execution. No public exploit code was identified in the provided data, and reachability of a working gadget chain determines whether impact reaches full RCE.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.
No patch listed yet 0.3% exploitation probability (EPSS)

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AnalysisAIv1 – Oct 10, 2026

Unauthenticated PHP object injection in the WordPress theme Windsor (ThemeREX) through version 2.10 lets remote attackers feed crafted serialized data into an unserialize() call reachable without authentication or user interaction, scoring a maximum base 9.8 under CVSS 3.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H). Reported by Patchstack and tracked as CWE-502, the flaw's realized impact depends on whether a usable PHP gadget chain exists across the theme, WordPress core, and installed plugins - in an unpatched site with a suitable gadget, this can escalate to code execution, arbitrary file or data manipulation, whereas without one the injection may be largely inert. At time of analysis there is no public exploit code identified and no CISA KEV listing, so exploitation is not confirmed in the wild; no vendor-released fix version appears in the available advisory data. Given the unauthenticated, network-reachable profile and the prevalence of gadget-rich plugin stacks, this should be treated as high priority for any site running the theme.

RemediationAI

No vendor-released patch version is identified in the available advisory data for Windsor at or below 2.10, so the primary action is to check the ThemeREX distribution channel and the Patchstack advisory (https://patchstack.com/database/wordpress/theme/windsor/vulnerability/wordpress-windsor-theme-2-10-php-object-injection-vulnerability?_s_id=cve) for a fixed release and apply it as soon as one is published. Until a patched version exists, the most effective control is to deactivate and remove the Windsor theme from production sites and replace it with an actively maintained alternative - the side effect being a theme migration effort, which is the strongest risk reduction available given this is an unauthenticated, network-reachable flaw with full C/I/A impact in the worst case. If the theme must stay in place, keep it inactive when not in use, move it out of the web root so its files are not directly reachable, and constrain exposure by fronting wp-content/themes/windsor paths with a WAF rule that blocks requests containing serialized-object markers such as 'O:' followed by a class name in parameters; this reduces but does not eliminate risk, since payload encoding can bypass naive pattern matching. Additionally, audit the installed plugin and core footprint for known gadget chains and remove unused plugins, because the practical severity of this object injection depends on whether a reachable gadget exists on the target - eliminating gadget sources lowers the chance the primitive becomes code execution. Finally, monitor logs for anomalous requests to theme endpoints and treat any such activity as a potential compromise signal pending a vendor fix.

Affected VersionsENISA

Windsor n/a ≤2.10

Affected Packages

euvd windsor no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The vulnerability is a classic PHP object injection (CWE-502, deserialization of untrusted data) in the Windsor WordPress theme by ThemeREX, affecting the version range covered by the CPE cpe:2.3:a:themerex:windsor:*:*:*:*:*:*:*:* up to and including 2.10. Control flow reaches a PHP unserialize() call that accepts attacker-controlled input from a remote, unauthenticated request; because unserialize() reconstructs arbitrary PHP objects and invokes their magic methods (__wakeup, __destruct, __toString, and similar), an attacker who controls the serialized string controls object instantiation inside the WordPress process. Object injection is a primitive rather than an end in itself: its severity crystallizes only when an exploitable 'gadget chain' - a sequence of magic-method calls across theme classes, WordPress core classes, or classes registered by installed plugins - can be chained to reach a sensitive sink such as file write, file deletion, SQL execution, or callable dispatch. The supplied CVSS vector assigns the maximal application-layer impact profile (S:U, C:H/I:H/A:H) with no privileges or interaction required, which reflects the assumed worst case where such a chain is reachable; the independent assessment notes that realistic risk is bounded by the specific theme/core/plugin combination deployed, since a site lacking a reachable gadget chain may see only inert or limited injection behavior. PHP 7.x/8.x will emit warnings or throw on malformed serialized input, but validly structured payloads bypass those safeguards entirely, which is why object injection remains a high-signal class in WordPress ecosystems.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (Patchstack) PRIMARY 9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vuln.today AI 9.8 CRITICAL

Network-reachable, unauthenticated unserialize() injection (AV:N/PR:N/UI:N); AC:L retained to match the reported no-auth profile, with full C/I/A assuming a reachable gadget chain.

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 (Patchstack).

CVSS VectorVendor: Patchstack

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionCVE.org

Unauthenticated PHP Object Injection in Windsor <= 2.10 versions.

Executive ViewAI

Why It Matters

Any internet-facing WordPress site running the ThemeREX "Windsor" theme at version 2.10 or earlier can be reached by an unauthenticated, remote attacker who may be able to manipulate site data or execute code, with no login or user interaction required and no public exploit identified at time of analysis. Because the theme sits on publicly reachable web infrastructure and the realized impact depends on whether a usable PHP gadget chain exists across the site's plugins and core, leadership should treat this as a material risk to web presence, customer data, and brand trust until the theme is removed or a vendor fix is released. No vendor-released patch has been identified, so affected sites remain exposed for the foreseeable near term.

Business Impact: Severe
Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: deactivate and remove the Windsor theme (versions through 2.10) from all sites; apply WAF virtual patching to block crafted serialized-object payloads reaching theme endpoints; restrict access to theme entry points and administrative interfaces; reduce available PHP gadget chains by removing unused plugins and themes; and monitor logs and file integrity for deserialization attempts and unexpected changes.

Threat Intelligence Overview

EPSS Score
0.3%
Top 78% exploitable
Prevalence
Low
niche ThemeREX commercial WordPress theme, limited site footprint
Data Quality
5 sources
Confidence: Medium

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.3%
Patch available No
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Out-of-Cycle
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

49
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +49
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Insecure deserialization occurs when an application converts serialized data (a stream of bytes representing an object's state) back into a living object without proper validation.

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