CVE-2026-5743 in SimpLy Gallery Plugin
Summary
by MITRE • 07/11/2026
The SimpLy Gallery Block & Lightbox plugin for WordPress is vulnerable to Stored Cross-Site Scripting via block attributes in all versions up to, and including, 3.3.3.2. This is due to insufficient input sanitization and output escaping on the sliderMaxHeight block attribute in the pgc_sgb_render_callback() function. The vulnerability exists because the pgc_sgb_sanitize_custom_css() function uses a flawed regex pattern that only removes event handlers with quoted values (e.g., onfocus="alert()") but fails to catch unquoted event handlers (e.g., onfocus=alert(document.cookie)), allowing the malicious code to bypass sanitization. This makes it possible for authenticated attackers, with Author-level access and above, to inject arbitrary web scripts in pages via block attributes that will execute whenever a user accesses an injected page.
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Analysis
by VulDB Data Team • 07/11/2026
The SimpLy Gallery Block & Lightbox WordPress plugin presents a critical stored cross-site scripting vulnerability that affects all versions up to and including 3.3.3.2. This vulnerability resides within the pgc_sgb_render_callback() function where block attributes are processed, specifically targeting the sliderMaxHeight parameter. The flaw stems from inadequate input sanitization mechanisms that fail to properly validate and escape user-supplied data before rendering it in web pages. Security researchers have identified that the plugin's pgc_sgb_sanitize_custom_css() function employs a regex pattern that demonstrates a fundamental weakness in its defensive approach, as it only effectively removes event handlers when they are enclosed in quotes, leaving unquoted event handlers vulnerable to exploitation.
The technical implementation of this vulnerability follows CWE-79 standards for cross-site scripting flaws, where user-controllable data is improperly sanitized before being rendered in web pages. The specific regex pattern used in the sanitization process creates a bypass condition that allows attackers to inject malicious JavaScript code through unquoted event handlers such as onfocus=alert(document.cookie) while quoted versions like onfocus="alert()" are properly removed. This selective sanitization approach creates a security gap that authenticated attackers with Author-level privileges or higher can exploit to inject persistent malicious scripts into the plugin's block attributes. The vulnerability operates at the application layer and represents a classic stored XSS attack vector where malicious code becomes permanently embedded in the plugin's data storage and executes whenever affected pages are accessed.
The operational impact of this vulnerability extends beyond simple script execution, as it enables attackers to perform various malicious activities including session hijacking, credential theft, and data exfiltration. Since authenticated users with Author-level access can exploit this flaw, it represents a significant risk to WordPress sites where such privileges might be compromised or granted to untrusted users. The stored nature of the vulnerability means that once injected, malicious scripts will execute automatically whenever any user accesses pages containing the affected block attributes, creating a persistent threat vector. This weakness allows attackers to potentially establish backdoors, manipulate content, or redirect users to malicious sites while maintaining long-term access to the compromised system.
Mitigation strategies should focus on immediate patching of the plugin to version 3.3.3.3 or later where the sanitization logic has been properly updated to handle both quoted and unquoted event handlers through comprehensive regex patterns. Administrators should implement additional security measures including role-based access control restrictions, limiting the number of users with Author-level privileges, and regular monitoring of plugin updates. The remediation process must address the underlying CWE-79 vulnerability by ensuring that all user-controllable inputs are properly escaped before rendering, implementing Content Security Policy headers to prevent script execution, and conducting thorough security testing of all plugin components. Additionally, organizations should consider implementing web application firewalls and intrusion detection systems to monitor for suspicious activity related to XSS attack patterns in their WordPress environments while following ATT&CK framework guidelines for defending against malicious code injection techniques.