CVE-2026-40806

Executive Summary

CVE-2026-40806 is an unauthenticated Reflected/Stored Cross-Site Scripting (XSS) vulnerability (CWE-79) affecting the WordPress plugin "Blog, Posts and Category Filter for Elementor" in versions up to and including 2.1.0. The flaw is reachable without authentication and requires user interaction to weaponize, carrying a CVSS v3.1 base score of 7.1 (High). Successful exploitation allows injection of arbitrary JavaScript into a victim's browser session within the context of the affected WordPress site, enabling session theft, credential harvesting, malicious redirects, or administrative actions on behalf of the victim.

Technical Analysis

The affected component is a WordPress plugin whose stated function is to provide filtering controls for blog posts and categories within Elementor page-builder layouts. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting.

The CVSS v3.1 vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L establishes the following characteristics that can be asserted with confidence:

• AV:N (Network) — The attack is delivered over the network, consistent with a web-facing WordPress plugin endpoint accessible via HTTP/HTTPS.
• AC:L (Low) — No special conditions or race windows are required; the attack is straightforward once a suitable input surface is identified.
• PR:N (None) — No authentication is required. The attacker does not need a valid WordPress account, contributor role, or session. This is the defining "Unauthenticated" attribute called out in the NVD description.
• UI:R (Required) — Exploitation depends on a victim user visiting a crafted URL, loading a page containing the injection, or otherwise triggering rendering of the malicious content. This mirrors typical reflected-XSS chains where the payload is not automatically executed without victim action.
• S:C (Changed) — The security authority scope changes. The vulnerable component is the plugin, but the attacker's injected script executes in the context of the broader WordPress site origin, potentially affecting resources outside the plugin's own boundary (e.g., authenticated admin sessions, other pages under the same domain).
• C:L / I:L / A:L (Low confidentiality, integrity, and availability) — Impact is bounded but non-trivial: attacker scripts operate with the privileges of the victim's browser session in the site origin, allowing read of data visible to that context, modification of rendered content, and limited disruption.

Because the NVD description does not disclose the specific parameter, endpoint, HTTP method, or sanitization routine involved, no implementation-level detail (function names, query parameters, AJAX action hooks, or file paths) can be asserted here without fabrication. What is known is the vulnerability class: the plugin fails to properly neutralize user-controllable input before reflecting or storing it into HTML output served to other users. Given the "Unauthenticated" designation and the plugin's nature as a front-end filter UI, the input surface is most plausibly exposed through publicly reachable request handling associated with the blog/posts/category filtering feature.

Exploitation Scenarios

No public proof-of-concept, Nuclei template, or exploit code is available for CVE-2026-40806. The attack chain below is therefore inferred strictly from the vulnerability class (unauthenticated XSS) and the data provided; no specific parameter names, URLs, or code constructs are asserted.

1. Reconnaissance / target identification. An attacker enumerates WordPress sites running the "Blog, Posts and Category Filter for Elementor" plugin at version <= 2.1.0. Passive fingerprinting can leverage page source artifacts, plugin asset paths, or Shodan queries (see METADATA dorks) to locate candidates without touching the target directly.

2. Triggering the flaw class. Because the vulnerability is unauthenticated, the attacker does not need an account. The attacker crafts a request containing a script payload to whichever plugin-exposed input surface reaches HTML output without proper neutralization. For a reflected XSS variant, the payload is embedded in a URL the attacker then lures a victim to open; for a stored variant, the attacker submits content that is persisted and later rendered to other visitors or administrators. The specific injection point is not disclosed in available data and is not fabricated here.

3. Payload / execution method (class level). The injected payload is JavaScript delivered to the victim's browser. When the victim loads the crafted page or link (satisfying UI:R), the script executes in the origin of the affected WordPress site (S:C), operating with the victim's session context. Typical objectives at this stage include accessing cookies or tokens that are not HttpOnly, scraping page content, or issuing same-origin requests that the site will honor as the victim.

4. Post-exploitation impact. Injected script achieves low-level confidentiality and integrity impact as scored: exfiltration of session- or page-visible data, content tampering, redirection to attacker-controlled pages, or silent same-origin actions. Where a site administrator is the victim, the changed-scope rating reflects the potential for the attacker to reach administrative functionality within the site origin — though the CVSS subscores cap that impact at Low.

Impact Assessment

The CVSS v3.1 base score is 7.1 (High). The score is driven by network reachability (AV:N), no authentication prerequisite (PR:N), low attack complexity (AC:L), and changed scope (S:C), partially offset by the requirement of victim interaction (UI:R) and low confidentiality/integrity/availability subscores.

• Affected systems: Any WordPress installation running "Blog, Posts and Category Filter for Elementor" at version <= 2.1.0. No affected-version exceptions are documented; all builds in that range should be considered vulnerable.
• Blast radius: The plugin itself is the entry point, but the executed script runs in the origin of the entire affected website, meaning impact is not confined to plugin-rendered pages. Visitors, authenticated users, and potentially site administrators are viable victims.
• Business impact: Session hijacking of high-privilege users can lead to unauthorized content modification, defacement, SEO poisoning payload delivery, credential phishing, or watering-hole style redirection of a trusted brand domain. Because no patch exists (0/4 patch confidence) and no KEV listing or EPSS score is available, defenders cannot rely on upstream fixes as a compensating control; exposure persists until mitigations are applied at the edge or WAF layer.

Detection Guidance

Sigma Rule

title: Possible Unauthenticated XSS Exploitation Attempt - Blog Posts Category Filter for Elementor
id: 7d4a1f2b-9c11-4e0a-9a7e-2f5b40806cve
status: experimental
description: Detects web requests to WordPress sites containing common XSS payload markers targeting Elementor-related filtering parameters.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-40806
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_method:
    cs-method:
      - 'GET'
      - 'POST'
  selection_payload:
    cs-uri-query|contains:
      - '<script'
      - '%3Cscript'
      - 'javascript:'
      - 'onerror='
      - 'onload='
      - 'svg/onload'
      - 'alert('
      - 'document.cookie'
  selection_context:
    cs-uri-query|contains:
      - 'elementor'
      - 'category'
      - 'filter'
      - 'posts'
  condition: selection_method and selection_payload and selection_context
falsepositives:
  - Legitimate security scanners
  - Application fuzzing in non-production
level: medium

YARA Rule

rule CVE_2026_40806_Elementor_XSS_Payload
{
    meta:
        description = "Detects common reflected/stored XSS payload artifacts associated with CVE-2026-40806"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-40806"
        date = "2026-01-01"
        severity = "high"

    strings:
        $s1 = "<script>" ascii nocase
        $s2 = "</script>" ascii nocase
        $s3 = "javascript:" ascii nocase
        $s4 = "onerror=" ascii nocase
        $s5 = "onload=" ascii nocase
        $s6 = "document.cookie" ascii nocase
        $s7 = "svg/onload" ascii nocase
        $s8 = "alert(1)" ascii nocase

    condition:
        uint16(0) == 0x3C3F or
        (2 of ($s*) and filesize < 4096)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-40806 Possible Unauthenticated XSS in Blog Posts Category Filter for Elementor"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"elementor"; nocase; http.uri; content:"category"; nocase; pcre:"/(%3C|\\x3C)script|javascript:|onerror=|onload=|svg\/onload/i"; classtype:web-application-attack; reference:cve,2026-40806; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-40806; metadata:created_at 2026_01_01, updated_at 2026_01_01; sid:202640806; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=30s
  [network where http.request.method in ("GET", "POST") and
     http.request.uri : ("*elementor*" or "*category*" or "*filter*")]
  [network where http.request.uri : ("*<script*" or "*%3Cscript*" or "*javascript:*" or
     "*onerror=*" or "*onload=*" or "*svg/onload*" or "*document.cookie*")]

Splunk SPL Query

index=web sourcetype=access_combined OR sourcetype=nginx:access
| eval uri_lower=lower(uri)
| where (like(uri_lower, "%elementor%") OR like(uri_lower, "%category%") OR like(uri_lower, "%filter%"))
| where (like(uri_lower, "%<script%") OR like(uri_lower, "%3cscript%") OR like(uri_lower, "%javascript:%")
    OR like(uri_lower, "%onerror=%") OR like(uri_lower, "%onload=%") OR like(uri_lower, "%svg/onload%")
    OR like(uri_lower, "%document.cookie%"))
| stats count min(_time) AS first_seen max(_time) AS last_seen by src_ip, uri, status
| sort - count

Wazuh OSSEC Rule

<group name="web,appsec,wordpress,xss,">
  <rule id="2026408" level="10">
    <decoded_as>web-accesslog</decoded_as>
    <match>elementor</match>
    <regex type="pcre2">(?i)(%3C|<)script|javascript:|onerror=|onload=|svg/onload|document\.cookie</regex>
    <description>CVE-2026-40806: Possible unauthenticated XSS exploitation attempt in Blog, Posts and Category Filter for Elementor (<=2.1.0)</description>
    <mitre>
      <id>T1059.007</id>
    </mitre>
    <group>attack,xss,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations. Because no vendor fix exists, treat this as a persisting exposure:

   • Deploy virtual patching at the WAF/reverse proxy layer targeting XSS payload patterns (see Suricata/Sigma content above) on requests to any plugin-related endpoints.
   • Deactivate and, if practical, remove the "Blog, Posts and Category Filter for Elementor" plugin until a fixed version ships. If filtering functionality is essential, replace it with an actively maintained alternative.
   • Enforce a strict Content-Security-Policy for the WordPress origin to limit inline script execution and reduce the impact of any successful injection.
   • Ensure session cookies are set HttpOnly and Secure to reduce token theft from injected scripts.
   • Apply WordPress core hardening: restrict file editing, enforce least-privilege roles, and require re-authentication for administrative actions.

2. Patch / upgrade steps. No patched version is available from any tracked source, and no vendor advisory has been published as of this report. Monitor the plugin vendor channel and the WordPress plugin repository for a version above 2.1.0 that explicitly addresses CVE-2026-40806. Do not assume a newer release is fixed without a vendor changelog or advisory confirming it. Until such confirmation exists, maintain plugin removal or WAF mitigation as the standing posture.

3. Long-term hardening. Adopt a plugin lifecycle policy that retires components with no security-maintenance cadence; track plugin CVEs through automated SCA/WP-CLI vulnerability scans; enforce HTTPS and HSTS; and implement output encoding and input validation standards in any custom WordPress integrations that echo user-controlled data.

References

• NVD — CVE-2026-40806: https://nvd.nist.gov/vuln/detail/CVE-2026-40806
• CWE-79 — Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'): https://cwe.mitre.org/data/definitions/79.html
• MITRE ATT&CK — T1059.007 Command and Scripting Interpreter: JavaScript: https://attack.mitre.org/techniques/T1059/007/
• WordPress Plugin Security documentation: https://developer.wordpress.org/plugins/security/
• CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-40806 is not listed as of this report)

No public proof-of-concept, exploit code, Nuclei template, or in-the-wild campaign telemetry is available for CVE-2026-40806 at the time of writing. No EPSS score has been assigned by FIRST.org; no EPSS value is asserted. All exploitation detail in this report is derived from the vulnerability class and supplied CVSS data only.