CVE-2026-81290 in Email Subscribers & Newsletters Plugin
Summary
by MITRE • 08/31/2026
Unauthenticated Cross Site Scripting (XSS) in Email Subscribers & Newsletters <= 5.9.33 versions.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified as an unauthenticated cross-site scripting flaw within the Email Subscribers and Newsletters plugin for WordPress, affecting versions up to 5.9.33, represents a significant security risk due to its lack of authentication requirements. This specific characteristic allows any internet user, regardless of their login status or privilege level on the target website, to exploit the weakness. The core technical flaw typically stems from insufficient sanitization and validation of user-supplied input before it is processed by the application's backend logic or rendered in the browser context. In many cases involving newsletter plugins, this involves parameters related to subscription forms, unsubscribe links, or administrative settings that are exposed via HTTP requests without proper access control checks. When malicious scripts are injected into these fields and subsequently stored on the server or reflected back to users during page loads, they execute within the victim's browser session under the trust context of the vulnerable website.
From a technical perspective, this vulnerability aligns with CWE-79, which classifies improper neutralization of input during web page generation as Cross-site Scripting. The attack vector often involves injecting JavaScript code into fields such as name, email address, or custom message boxes within subscription forms. Because the plugin fails to properly encode special characters like angle brackets and quotes before outputting them back to the client, the browser interprets these inputs as executable commands rather than plain text data. This execution environment allows attackers to bypass same-origin policies that normally restrict scripts from interacting with content on different domains, thereby enabling a wide range of malicious activities including session hijacking, credential theft via keyloggers, or defacement of the website's user interface.
The operational impact of this vulnerability is severe because it compromises the integrity and confidentiality of both the administrator account and end-user data without requiring any prior authentication. An attacker can craft a phishing link containing the malicious payload and distribute it through social engineering channels such as email or messaging apps. When an administrator or even a regular subscriber clicks on the link, the script executes automatically in their browser. This can lead to the theft of administrative cookies, allowing the attacker to take full control of the WordPress dashboard. Furthermore, since newsletter plugins often handle sensitive user data including names and email addresses for marketing purposes, successful exploitation could result in the exfiltration of this personal information to remote servers controlled by the threat actor, leading to potential violations of privacy regulations such as GDPR or CCPA.
In terms of industry frameworks, this vulnerability maps directly to MITRE ATT&CK technique T1059, specifically sub-technique 007 for JavaScript execution within a web browser context. It also relates to TA0003 Persistence if the attacker uses the compromised session to install additional malicious plugins or modify site settings to maintain access. The unauthenticated nature of the exploit places it in high severity categories across most vulnerability scoring systems due to the ease of exploitation and broad attack surface available to remote adversaries who do not need valid credentials.
To mitigate this risk, immediate action is required by upgrading the Email Subscribers and Newsletters plugin to version 5.9.34 or later where these input validation issues have been addressed through enhanced sanitization routines and stricter output encoding practices. Administrators should also implement a Web Application Firewall that includes rules for detecting common XSS payloads in HTTP request parameters, providing an additional layer of defense against exploitation attempts while the patch is being applied. Regular security audits and code reviews focusing on user input handling are recommended to prevent similar vulnerabilities from arising in other parts of the application stack.