CVE-2026-109989 in Themify Popup Plugin
Summary
by MITRE • 10/17/2026
The Themify Popup plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'popup_width_unit' parameter in all versions up to, and including, 1.4.7 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with author-level access and above, 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 • 10/17/2026
The Themify Popup plugin for WordPress contains a critical security flaw identified as Stored Cross-Site Scripting within the popup_width_unit parameter across all versions up to 1.4.7. This vulnerability stems from insufficient input sanitization and output escaping mechanisms, which allow malicious actors to inject arbitrary web scripts into the application's database. The core technical failure lies in the plugin's handling of user-supplied data during configuration updates, where specific parameters are not adequately validated against expected formats or escaped before being rendered in HTML contexts. This lack of rigorous validation creates a direct pathway for code injection that persists on the server side rather than occurring transiently within a single request session.
The operational impact of this vulnerability is significant due to its stored nature and the required privilege level. Attackers must possess authenticated access with author-level permissions or higher, which limits the attack surface but increases the potential severity once achieved. By exploiting this flaw, an attacker can embed malicious JavaScript code that becomes part of the page content itself. Consequently, every user who accesses a page containing the injected payload will have their browser execute the script automatically. This persistent execution model facilitates widespread compromise if multiple users view the affected pages, leading to session hijacking, credential theft, defacement, or redirection to phishing sites without any further interaction from the victim beyond viewing the content.
From an industry standards perspective, this vulnerability aligns with CWE-79 Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The specific mechanism involves stored payloads that remain active until manually removed, distinguishing it from reflected variants. In terms of tactical classification under MITRE ATT&CK for Enterprise and Mobile, this behavior corresponds to T1059 Command and Control via Application Layer Protocol or more specifically the execution phase where scripts are run on client systems. The persistence aspect also relates to techniques involving content injection that maintain access over time without requiring repeated exploitation attempts by the adversary.
Mitigation strategies should prioritize immediate remediation through software updates. Administrators must upgrade the Themify Popup plugin to version 1.4.8 or later, where these sanitization and escaping issues have been addressed by the developers. In environments where upgrading is not immediately feasible, temporary mitigations include restricting author-level access to trusted individuals only and implementing Web Application Firewall rules that detect and block common XSS payload patterns in POST requests targeting the relevant endpoints. Additionally, enabling Content Security Policy headers can help mitigate the impact of any successfully injected scripts by restricting the sources from which executable content may be loaded, thereby reducing the effectiveness of the attack even if exploitation occurs.