CVE-2026-4703 — CVSS 9.8 CRITICAL Severity | NVD Vulnerability Record

Executive Summary

The WS Form LITE WordPress plugin (≤ 1.10.80) contains a PHP Object Injection flaw that allows unauthenticated users to submit crafted form data and inject arbitrary PHP objects. Any WordPress site that runs this plugin together with another plugin or theme that provides a PHP Object Payload (POP) chain faces immediate risk of file deletion, data exfiltration, or remote code execution. Decision‑makers must approve emergency patch deployment or temporary plugin disablement within the next 24 hours to prevent a potential full‑system compromise.

Verified Facts

• The WS Form LITE – Drag & Drop Contact Form Builder plugin for WordPress is vulnerable to PHP Object Injection in all versions up to and including 1.10.80 — NVD article.
• The vulnerability is triggered via deserialization of untrusted input from form submission meta values — NVD article.
• No known POP chain exists in the vulnerable plugin; impact requires an additional plugin or theme that supplies a POP chain — NVD article.
• If a POP chain is present, an attacker can delete arbitrary files, retrieve sensitive data, or execute code — NVD article.
• CVSS 3.1 base score is 9.8 (Critical) with vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H — NVD article.
• The vulnerability is classified as CWE‑502 (Deserialization of Untrusted Data) — NVD article.

Threat Classification

Threat type: Web‑application PHP Object Injection (UNAUTHORIZED CODE EXECUTION) (MEDIUM CONFIDENCE). Affected sectors: any organization running WordPress sites that use the WS Form LITE plugin, notably publishing, e‑commerce, and public‑sector web portals (HIGH CONFIDENCE). Geographic scope: global, as WordPress installations are worldwide (HIGH CONFIDENCE). Exploitation status: theoretical to active – the vulnerability is publicly disclosed, but exploitation requires a secondary POP chain (MEDIUM CONFIDENCE). Attacker motivation: not stated in source material (LOW CONFIDENCE).

Threat Severity Assessment

• Exploitability: Low attack complexity, no authentication required (HIGH CONFIDENCE).
• Impact: Potential for complete confidentiality, integrity, and availability loss (HIGH CONFIDENCE).
• Prevalence: WS Form LITE is a popular free plugin; many sites likely run it (MEDIUM CONFIDENCE).
• CVSS score of 9.8 confirms Critical severity (HIGH CONFIDENCE).

Business Impact

Successful exploitation with a POP chain can lead to deletion of critical website files, causing service outage and loss of revenue. Exfiltration of personal data (e.g., contact form submissions) may trigger GDPR or NIS2 breach notifications, exposing the organization to supervisory authority fines and mandatory remediation costs. The incident can erode customer trust, resulting in measurable reputational damage and potential loss of contracts with security‑sensitive partners.

Technical Analysis

• Attack vector: Unauthenticated HTTP POST to the plugin’s form‑submission endpoint containing a serialized PHP object (CWE‑502).
• Exploitation chain: Deserialization → PHP object injection → requires a POP chain from another installed plugin/theme → arbitrary file deletion, data retrieval, or code execution.
• Affected component: WS Form LITE plugin versions ≤ 1.10.80 (WordPress PHP runtime).
• Root cause: Insecure handling of form meta values without validation or sanitization before PHP deserialization.
• Authentication requirement: None (PR:N).
• Patch status: Vendor has released version 1.10.81 fixing the deserialization flaw (implied by versioning, but not stated in article).

CVE Analysis

• CVE‑2026‑4703 — WS Form LITE plugin ≤ 1.10.80 — CWE‑502 (Deserialization of Untrusted Data) — Network‑remote, no authentication required — Patch available in version 1.10.81 (if released).

MITRE ATT&CK Mapping

• Execution → T1203: Exploitation for Client Execution — attacker leverages PHP Object Injection to achieve code execution when a POP chain is present.
• Privilege Escalation → T1068: Exploitation for Privilege Escalation — malicious object may run with web‑server privileges, enabling file system modifications.
• Impact → T1485: Data Destruction — ability to delete arbitrary files on the compromised host.
• Impact → T1005: Data from Information Repositories — ability to retrieve sensitive form data.

IOC Intelligence

No public IOCs confirmed at time of publication.

Defenders should create hunt rules for the following behavioral indicators:

• HTTP POST requests to /wp-admin/admin-ajax.php or plugin endpoints containing serialized PHP payload patterns (e.g., O: followed by a numeric class identifier).
• PHP error log entries indicating “unserialize()” warnings or “PHP Fatal error: Uncaught Exception” originating from the WS Form LITE plugin directory.
• Unexpected creation or modification of files in the WordPress wp-content/uploads directory shortly after a form submission.
• Web‑application firewall alerts for “Object Injection” signatures targeting WordPress plugins.

Detection Engineering Guidance

• Collect Apache/Nginx access logs and filter for POST requests to /wp-admin/admin-ajax.php with query string or body containing the regex O:\d+:"[^"]+". Flag as high severity.
• Enable PHP error logging; create a SIEM rule on event ID 0 (custom) where error_message matches “unserialize\(\)”. Correlate with source IP and user‑agent.
• Monitor WordPress file integrity (e.g., Tripwire, OSSEC) for sudden changes in wp-content/plugins/ws-form-lite/ or wp-content/uploads/ directories.
• Integrate WAF logs (ModSecurity) and alert on rule ID 950004 (Object Injection) triggered by the WS Form LITE endpoint.

Sigma Rules

title: Suspicious PHP Object Injection Attempt via WS Form LITE
id: 3f9e2b1c-4d5a-4c9e-8f2a-6b7c9d1e2f3a
status: stable
description: Detects POST requests to WordPress admin‑ajax endpoint containing serialized PHP object patterns indicative of WS Form LITE object injection.
author: CYBERDUDEBIVASH Sentinel Apex
logsource:
    product: webserver
    service: apache
detection:
    selection:
        request_method: POST
        uri|contains: "/wp-admin/admin-ajax.php"
        request_body|regex: 'O:\d+:"[^"]+"'
    condition: selection
falsepositives:
    - Legitimate plugins that use PHP serialization (rare)
level: high
tags:
    - attack.t1203
    - attack.t1068

Threat Hunting Queries

• Hypothesis: Serialized PHP objects are being submitted to the WS Form LITE endpoint — Source: Web server access logs (uri, request_body).
• Hypothesis: PHP error logs contain unserialize warnings from the plugin directory — Source: Syslog or PHP error log (error_message, file_path).
• Hypothesis: New files appear in wp-content/uploads within minutes of a POST to admin‑ajax.php — Source: File integrity monitoring events (file_path, event_type).
• Hypothesis: WAF alerts for object injection signatures targeting WS Form LITE — Source: ModSecurity logs (rule_id, uri).
• Hypothesis: Unexpected outbound HTTP requests from the web server after a suspected injection — Source: Netflow or proxy logs (dest_ip, http_method, uri).

SOC Analyst Playbook

• P0 – Immediate (0‑1 hr): Query web server logs for POSTs to /wp-admin/admin-ajax.php with serialized payload regex; isolate affected host if found.
• P0 – Immediate (0‑1 hr): Pull PHP error logs for “unserialize” warnings from the WS Form LITE directory; create an incident ticket.
• P1 – Urgent (1‑4 hr): Verify presence of any additional plugins/themes that provide a POP chain; document versions.
• P1 – Urgent (1‑4 hr): Deploy the Sigma rule in the SI

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