CVE-2026-91011 in EWWW Image Optimizer Plugin
Summary
by MITRE • 09/17/2026
The EWWW Image Optimizer WordPress plugin before 8.7.7 does not properly escape image attribute values when it rewrites page output, allowing authenticated users with author-level access and above to inject arbitrary JavaScript that is stored in published content and executes in the browser of any user who later views the affected page.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in EWWW Image Optimizer versions prior to 8.7.7 represents a critical Stored Cross-Site Scripting (XSS) flaw rooted in insufficient input validation and output encoding mechanisms within the plugin's image processing pipeline. This security defect specifically manifests when the plugin rewrites page output, a process intended to optimize images for web delivery by modifying HTML attributes such as width, height, or alt text. The core technical failure lies in the improper escaping of these attribute values during the rewriting phase. Instead of applying strict sanitization protocols that adhere to context-specific encoding rules, the software allows raw user-supplied data to be inserted directly into the DOM structure without adequate protection against script injection vectors. This lack of robust output encoding creates a direct pathway for malicious actors to inject arbitrary JavaScript code into the rendered HTML content.
The operational impact of this vulnerability is significant due to its stored nature and the relatively low privilege threshold required for exploitation. An attacker with authenticated access at the author level or higher can embed malicious scripts within image metadata or attributes during the upload or editing process. Because the payload is stored in published content, it persists on the server side rather than being transient like reflected XSS attacks. Consequently, every user who subsequently views a page containing the compromised image will have their browser execute the injected JavaScript code automatically. This persistence transforms what might otherwise be an isolated incident into a widespread compromise affecting all visitors to the affected site, including potential administrators or users with sensitive data access rights.
From a classification perspective, this vulnerability aligns closely with CWE-79, which defines Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The specific mechanism here involves attribute value injection, falling under subcategories that address context-specific encoding failures. In terms of the MITRE ATT&CK framework, this exploit maps to T1059.007, which covers JavaScript execution within web browsers, and potentially T1189, Drive-by Compromise if the script facilitates further malware delivery or credential harvesting through phishing pages loaded via the injected script. The attack vector leverages the trust users place in legitimate website content, making it particularly effective for social engineering campaigns aimed at stealing session cookies, capturing keystrokes, or performing actions on behalf of the victim within the context of the vulnerable WordPress site.
Mitigation strategies must prioritize immediate remediation through software updates and enhanced security configurations. The primary defense is to upgrade the EWWW Image Optimizer plugin to version 8.7.7 or later, where the developers have implemented proper escaping mechanisms for image attributes during output rewriting. For organizations unable to patch immediately due to compatibility constraints, implementing a Web Application Firewall (WAF) with rules specifically tuned to detect and block XSS payloads in HTTP requests related to media uploads can provide an additional layer of defense. Furthermore, enforcing strict Content Security Policy headers that restrict the execution of inline scripts can mitigate the impact by preventing the injected JavaScript from running even if it is successfully stored in the database. Regular security audits focusing on input validation and output encoding practices across all active plugins are essential to prevent similar vulnerabilities arising from other components within the WordPress ecosystem.