CVE-2026-3891

Critical

Published: 13 March 2026

Published

13 March 2026

Modified

22 April 2026

KEV Added

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Patch

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CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0008 23.2th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-3891 is a critical-severity Unrestricted Upload of File with Dangerous Type (CWE-434) vulnerability in Wordpress (inferred from references). Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 23.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 AC-3 (Access Enforcement) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 2 other techniques. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly remediates the arbitrary file upload vulnerability by requiring timely identification, reporting, and patching of the flawed plugin function.

SI-10 Information Input Validation good match

prevent

Enforces validation of file inputs to address the missing file type validation, preventing upload of dangerous files that could lead to RCE.

AC-3 Access Enforcement good match

prevent

Mandates enforcement of access control policies to implement the missing capability checks, blocking unauthenticated attackers from reaching the vulnerable upload function.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1505.003 Web Shell Persistence

Adversaries may backdoor web servers with web shells to establish persistent access to systems.

attack.mitre.org →

T1105 Ingress Tool Transfer Command And Control

Adversaries may transfer tools or other files from an external system into a compromised environment.

attack.mitre.org →

Why these techniques?

Arbitrary unauthenticated file upload in public-facing WordPress plugin directly enables initial access via T1190 (Exploit Public-Facing Application), installation of a web shell for execution/persistence via T1505.003, and ingress of malicious files via T1105.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

The Pix for WooCommerce plugin for WordPress is vulnerable to arbitrary file uploads due to missing capability check and missing file type validation in the 'lkn_pix_for_woocommerce_c6_save_settings' function in all versions up to, and including, 1.5.0. This makes it possible for…

unauthenticated attackers to upload arbitrary files on the affected site's server which may make remote code execution possible.

Deeper analysisAI

The Pix for WooCommerce plugin for WordPress is affected by CVE-2026-3891, a critical arbitrary file upload vulnerability in all versions up to and including 1.5.0. The issue arises from missing capability checks and file type validation in the `lkn_pix_for_woocommerce_c6_save_settings` function, classified under CWE-434 (Unrestricted Upload of File with Dangerous Type). Published on 2026-03-13, it has a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), reflecting its high severity due to potential for severe impacts across confidentiality, integrity, and availability.

Unauthenticated attackers can exploit this vulnerability remotely with low complexity and no user interaction or privileges required. By targeting the flawed function, they can upload arbitrary files to the affected WordPress site's server, which may enable remote code execution depending on the file type and server configuration.

Mitigation details are available in related advisories and plugin updates, including Wordfence threat intelligence at https://www.wordfence.com/threat-intel/vulnerabilities/id/20188fd3-c330-4c76-912b-72731e14c450?source=cve, source code at https://plugins.trac.wordpress.org/browser/payment-gateway-pix-for-woocommerce/tags/1.4.0/Includes/LknPaymentPixForWoocommercePixC6.php#L694, and changeset 3480639 at https://plugins.trac.wordpress.org/changeset/3480639/payment-gateway-pix-for-woocommerce#file56, which security practitioners should review for patching guidance beyond version 1.5.0.