CVE-2024-5878 is a medium severity vulnerability classified as CWE-79, indicating an improper neutralization of input during web page generation, commonly known as Cross-Site Scripting (XSS). This vulnerability affects multiple WordPress plugins that incorporate the SimpleLightbox JavaScript library version 2.1.5, developed by aknieriem. The root cause is insufficient input sanitization and output escaping of user-supplied attributes within the plugin. Authenticated attackers with contributor-level access or higher can exploit this flaw to inject arbitrary JavaScript code into pages. These malicious scripts execute whenever any user accesses the compromised page, potentially leading to session hijacking, defacement, or redirection to malicious sites. The vulnerability is exploitable remotely over the network without user interaction but requires the attacker to have authenticated privileges, which limits the attack surface to users with some level of access to the WordPress backend. The CVSS v3.1 base score is 6.4, reflecting a medium severity with network attack vector, low attack complexity, and privileges required. The scope is changed, meaning the vulnerability affects resources beyond the initially vulnerable component. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability was published on May 20, 2025, and has been enriched by CISA, indicating recognition by US cybersecurity authorities. The affected versions include all versions of the SimpleLightbox library bundled with WordPress plugins, making it a widespread issue for sites using these plugins.

For European organizations, this vulnerability poses a significant risk primarily to websites running WordPress with affected plugins. The ability for an authenticated contributor to inject persistent XSS payloads can lead to unauthorized actions on behalf of other users, data theft, or defacement, undermining trust and potentially violating data protection regulations such as GDPR. The impact is heightened for organizations relying on WordPress for customer-facing portals, intranets, or content management, where user sessions and sensitive information could be compromised. Although the vulnerability requires contributor-level access, many organizations allow multiple users with such privileges, increasing the risk of insider threats or compromised accounts. The persistent nature of the XSS means that the malicious code remains active until removed, potentially affecting many users over time. This could lead to reputational damage, financial loss, and regulatory penalties if personal data is exposed or manipulated. Additionally, the vulnerability could be leveraged as a foothold for further attacks within the network, especially if combined with other vulnerabilities or social engineering tactics.

European organizations should take immediate steps to mitigate this vulnerability beyond generic patching advice. First, identify all WordPress installations using plugins that bundle SimpleLightbox version 2.1.5 or earlier. Since no official patches are linked yet, organizations should consider temporarily disabling or removing affected plugins until updates are available. Implement strict user role management by limiting contributor-level access only to trusted personnel and regularly auditing user permissions. Employ Web Application Firewalls (WAFs) with custom rules to detect and block suspicious script injections targeting the affected plugin's endpoints. Conduct thorough input validation and output encoding on any custom code interacting with the plugin or user-generated content. Monitor website logs for unusual activity indicative of XSS exploitation attempts. Educate content contributors about the risks of uploading untrusted content or scripts. Once vendor patches are released, prioritize timely updates. Additionally, consider deploying Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts, mitigating the impact of any successful injection.