CVE-2026-107764 in CSS Plugin
Summary
by MITRE • 10/16/2026
The SiteOrigin CSS plugin for WordPress is vulnerable to Stored DOM-Based Cross-Site Scripting via the 'url (comment_author_url)' parameter in all versions up to, and including, 1.6.7 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. This is possible because WordPress core's esc_url() preserves HTML entity-encoded characters, allowing a crafted entity-encoded payload in the comment 'Website' field to survive storage and be DOM-decoded by the browser into executable markup at the sink.
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Analysis
by VulDB Data Team • 10/16/2026
The SiteOrigin CSS plugin for WordPress contains a critical security vulnerability affecting all versions up to and including 1.6.7, classified as a Stored Cross-Site Scripting (XSS) flaw. This vulnerability arises from insufficient input sanitization and output escaping mechanisms within the application's handling of user-supplied data. Specifically, the defect is located in the processing of the comment_author_url parameter, which corresponds to the Website field found in WordPress comments. The nature of this vulnerability allows unauthenticated attackers to inject arbitrary web scripts into pages that are subsequently served to other users. When a victim accesses a page containing the injected payload, the malicious script executes within the context of the vulnerable website, potentially leading to session hijacking, defacement, or further malware distribution.
The technical root cause of this vulnerability lies in the interaction between WordPress core functions and browser-side DOM parsing. The plugin fails to properly sanitize user input before storage and does not adequately escape output when rendering it back to the client. Crucially, the vulnerability exploits a specific behavior in the WordPress esc_url() function. While esc_url is designed to filter out dangerous protocols and characters from URLs, it preserves HTML entity-encoded characters. An attacker can craft a malicious payload using HTML entities that bypasses this filtering mechanism during storage. Because the data is stored without being decoded or further sanitized, when the page is rendered in a victim's browser, the DOM parser decodes these entities back into executable markup. This process effectively transforms what appears to be safe encoded text into active JavaScript code at the sink point where it is displayed.
From an operational impact perspective, this Stored XSS vulnerability poses significant risks to both website administrators and end-users. Since the attack does not require authentication, any visitor with access to the comment section can initiate the exploit. Once a victim views the compromised page, their browser executes the injected script in the context of the site's domain. This allows attackers to steal sensitive information such as session cookies, which could lead to unauthorized administrative access if an administrator is tricked into viewing the payload. Additionally, it enables phishing attacks where users are redirected to malicious sites mimicking legitimate pages. The persistent nature of stored XSS means that every user who views the affected page becomes a potential victim until the malicious content is removed from the database or patched in the plugin code.
To mitigate this vulnerability, immediate action is required by site administrators and developers. The primary remediation step is to upgrade the SiteOrigin CSS plugin to version 1.6.8 or later, where these input validation and output encoding issues have been addressed. For sites unable to update immediately due to compatibility constraints, a temporary workaround involves implementing custom server-side filtering to strip HTML entities from comment URLs before they are stored in the database. Additionally, deploying a Web Application Firewall (WAF) with rules specifically tuned to detect and block XSS payloads involving encoded characters can provide an additional layer of defense. It is also advisable to review other plugins for similar patterns where esc_url or similar functions might be misused without proper subsequent sanitization.
This vulnerability aligns with CWE-79, which describes Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The attack vector corresponds to ATT&CK technique T1059, specifically the execution of JavaScript via browser-based mechanisms. Understanding these mappings helps in categorizing the risk within broader security frameworks and ensures that mitigation strategies address both the immediate technical flaw and the underlying procedural gaps in input validation and output encoding practices. Regular audits of third-party plugins for adherence to secure coding standards are essential to prevent similar vulnerabilities from being introduced into WordPress environments.