The Responsive Lightbox & Gallery plugin for WordPress suffers from a Server-Side Request Forgery (SSRF) vulnerability identified as CVE-2026-2479. This vulnerability exists in all versions up to and including 2.7.1 due to improper hostname validation in the ajax_upload_image() function. Specifically, the plugin uses the PHP strpos() function to check if a hostname substring exists, rather than performing a strict hostname comparison. This flawed logic allows an authenticated attacker with Author-level privileges or higher to craft requests that the server will execute against arbitrary URLs, including internal network resources that are otherwise inaccessible externally. SSRF vulnerabilities can be leveraged to bypass firewall restrictions, access sensitive internal services, or perform further attacks such as data exfiltration or internal port scanning. The vulnerability does not require user interaction but does require authentication at the Author level or above, limiting the attacker scope to users with some level of trust. The CVSS 3.1 base score is 5.0, reflecting medium severity with network attack vector, low attack complexity, and privileges required. No public exploit code or active exploitation has been reported yet. The issue stems from a common programming error in input validation, highlighting the importance of strict hostname verification in SSRF defenses.

This SSRF vulnerability can have significant impacts on organizations running WordPress sites with the vulnerable Responsive Lightbox & Gallery plugin. Attackers with Author-level access can leverage the vulnerability to send arbitrary HTTP requests from the web server to internal systems, potentially exposing sensitive internal services, metadata endpoints, or administrative interfaces not intended for public access. This can lead to unauthorized information disclosure, internal network reconnaissance, and could serve as a pivot point for further attacks within the network. While the vulnerability does not directly allow data modification or denial of service, the ability to query internal resources can facilitate more complex attack chains. Organizations with sensitive internal infrastructure behind firewalls or segmented networks are particularly at risk. The requirement for authenticated access reduces the likelihood of widespread exploitation but insider threats or compromised accounts could exploit this flaw. Overall, the vulnerability poses a moderate risk to confidentiality and network security posture.

To mitigate CVE-2026-2479, organizations should first update the Responsive Lightbox & Gallery plugin to a version that addresses this vulnerability once released by the vendor. Until a patch is available, administrators should restrict Author-level and higher privileges to trusted users only, minimizing the risk of exploitation. Implement strict input validation and hostname verification in any custom code or plugin configurations to avoid substring matching pitfalls. Network segmentation and firewall rules should be enforced to limit the web server's ability to make outbound requests to sensitive internal services. Monitoring and logging of outbound HTTP requests from the web server can help detect suspicious SSRF attempts. Additionally, consider deploying Web Application Firewalls (WAFs) with SSRF detection capabilities to block malicious requests. Regularly audit user roles and permissions within WordPress to ensure least privilege principles are maintained. Finally, educate site administrators about the risks of SSRF and the importance of timely plugin updates.