CVE-2026-77365 in Optimole Plugin
Summary
by MITRE • 08/28/2026
The Optimole – Optimize Images | Convert WebP & AVIF | CDN & Lazy Load | Image Optimization plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'a' (above_fold_images) parameter in all versions up to, and including, 4.2.10 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
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Analysis
by VulDB Data Team • 08/28/2026
The Optimole plugin is a widely utilized WordPress extension designed to enhance website performance through image optimization, format conversion between WebP and AVIF, content delivery network integration, and lazy loading capabilities. While these features provide significant benefits for site speed and user experience, the underlying codebase in versions up to 4.2.10 contains critical security flaws that undermine the integrity of WordPress installations. The primary vulnerability identified is a Stored Cross-Site Scripting flaw located within the handling of the 'a' parameter, specifically associated with the above_fold_images functionality. This component determines which images are prioritized for loading in the visible portion of a web page to improve perceived performance metrics such as Largest Contentful Paint.
The technical root cause of this vulnerability lies in insufficient input sanitization and output escaping mechanisms within the plugin's code. When an attacker interacts with the affected parameter, the application fails to adequately validate or encode the supplied data before storing it in the database. Unlike reflected XSS where malicious scripts are executed immediately from a crafted URL, stored XSS persists because the injected payload is saved on the server side. Consequently, every time a legitimate user loads a page containing the compromised content, the browser interprets and executes the embedded JavaScript code as if it were part of the original webpage source. This persistence transforms a simple injection into a long-term threat vector that affects all visitors rather than just the attacker.
From an operational impact perspective, this vulnerability allows unauthenticated attackers to execute arbitrary web scripts in the context of any user viewing the affected pages. Since WordPress typically runs with elevated privileges depending on the user role, successful exploitation can lead to severe consequences including session hijacking, where attackers steal administrator cookies to gain full control over the website. It also enables data exfiltration, allowing malicious actors to scrape sensitive information from the victim's browser context, such as personal details or financial data if present in forms. Furthermore, stored XSS is frequently used to redirect users to phishing sites or to deploy further malware through drive-by downloads, significantly compromising the trust and security posture of the affected organization.
This vulnerability aligns with CWE-79, which classifies Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The attack vector is categorized under MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter: JavaScript, indicating that the attacker utilizes client-side scripting to execute actions within the victim's browser environment. To mitigate this risk, administrators must immediately update the Optimole plugin to version 4.2.11 or later where these sanitization issues have been addressed. In addition to patching, implementing a Web Application Firewall can provide an additional layer of defense by filtering out malicious payloads before they reach the application logic. Regular security audits and adherence to secure coding practices that enforce strict input validation and output encoding are essential for preventing similar vulnerabilities in future updates or other plugins within the WordPress ecosystem.